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Always turn off hyphenation; it makes +.\" way too many mistakes in technical documents. +.if n .ad l +.nh +.SH "NAME" +libev \- a high performance full\-featured event loop written in C +.SH "SYNOPSIS" +.IX Header "SYNOPSIS" +.Vb 1 +\& #include <ev.h> +.Ve +.Sh "\s-1EXAMPLE\s0 \s-1PROGRAM\s0" +.IX Subsection "EXAMPLE PROGRAM" +.Vb 2 +\& // a single header file is required +\& #include <ev.h> +\& +\& // every watcher type has its own typedef\*(Aqd struct +\& // with the name ev_<type> +\& ev_io stdin_watcher; +\& ev_timer timeout_watcher; +\& +\& // all watcher callbacks have a similar signature +\& // this callback is called when data is readable on stdin +\& static void +\& stdin_cb (EV_P_ struct ev_io *w, int revents) +\& { +\& puts ("stdin ready"); +\& // for one\-shot events, one must manually stop the watcher +\& // with its corresponding stop function. +\& ev_io_stop (EV_A_ w); +\& +\& // this causes all nested ev_loop\*(Aqs to stop iterating +\& ev_unloop (EV_A_ EVUNLOOP_ALL); +\& } +\& +\& // another callback, this time for a time\-out +\& static void +\& timeout_cb (EV_P_ struct ev_timer *w, int revents) +\& { +\& puts ("timeout"); +\& // this causes the innermost ev_loop to stop iterating +\& ev_unloop (EV_A_ EVUNLOOP_ONE); +\& } +\& +\& int +\& main (void) +\& { +\& // use the default event loop unless you have special needs +\& struct ev_loop *loop = ev_default_loop (0); +\& +\& // initialise an io watcher, then start it +\& // this one will watch for stdin to become readable +\& ev_io_init (&stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ); +\& ev_io_start (loop, &stdin_watcher); +\& +\& // initialise a timer watcher, then start it +\& // simple non\-repeating 5.5 second timeout +\& ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.); +\& ev_timer_start (loop, &timeout_watcher); +\& +\& // now wait for events to arrive +\& ev_loop (loop, 0); +\& +\& // unloop was called, so exit +\& return 0; +\& } +.Ve +.SH "DESCRIPTION" +.IX Header "DESCRIPTION" +The newest version of this document is also available as an html-formatted +web page you might find easier to navigate when reading it for the first +time: <http://cvs.schmorp.de/libev/ev.html>. +.PP +Libev is an event loop: you register interest in certain events (such as a +file descriptor being readable or a timeout occurring), and it will manage +these event sources and provide your program with events. +.PP +To do this, it must take more or less complete control over your process +(or thread) by executing the \fIevent loop\fR handler, and will then +communicate events via a callback mechanism. +.PP +You register interest in certain events by registering so-called \fIevent +watchers\fR, which are relatively small C structures you initialise with the +details of the event, and then hand it over to libev by \fIstarting\fR the +watcher. +.Sh "\s-1FEATURES\s0" +.IX Subsection "FEATURES" +Libev supports \f(CW\*(C`select\*(C'\fR, \f(CW\*(C`poll\*(C'\fR, the Linux-specific \f(CW\*(C`epoll\*(C'\fR, the +BSD-specific \f(CW\*(C`kqueue\*(C'\fR and the Solaris-specific event port mechanisms +for file descriptor events (\f(CW\*(C`ev_io\*(C'\fR), the Linux \f(CW\*(C`inotify\*(C'\fR interface +(for \f(CW\*(C`ev_stat\*(C'\fR), relative timers (\f(CW\*(C`ev_timer\*(C'\fR), absolute timers +with customised rescheduling (\f(CW\*(C`ev_periodic\*(C'\fR), synchronous signals +(\f(CW\*(C`ev_signal\*(C'\fR), process status change events (\f(CW\*(C`ev_child\*(C'\fR), and event +watchers dealing with the event loop mechanism itself (\f(CW\*(C`ev_idle\*(C'\fR, +\&\f(CW\*(C`ev_embed\*(C'\fR, \f(CW\*(C`ev_prepare\*(C'\fR and \f(CW\*(C`ev_check\*(C'\fR watchers) as well as +file watchers (\f(CW\*(C`ev_stat\*(C'\fR) and even limited support for fork events +(\f(CW\*(C`ev_fork\*(C'\fR). +.PP +It also is quite fast (see this +benchmark comparing it to libevent +for example). +.Sh "\s-1CONVENTIONS\s0" +.IX Subsection "CONVENTIONS" +Libev is very configurable. In this manual the default (and most common) +configuration will be described, which supports multiple event loops. For +more info about various configuration options please have a look at +\&\fB\s-1EMBED\s0\fR section in this manual. If libev was configured without support +for multiple event loops, then all functions taking an initial argument of +name \f(CW\*(C`loop\*(C'\fR (which is always of type \f(CW\*(C`struct ev_loop *\*(C'\fR) will not have +this argument. +.Sh "\s-1TIME\s0 \s-1REPRESENTATION\s0" +.IX Subsection "TIME REPRESENTATION" +Libev represents time as a single floating point number, representing the +(fractional) number of seconds since the (\s-1POSIX\s0) epoch (somewhere near +the beginning of 1970, details are complicated, don't ask). This type is +called \f(CW\*(C`ev_tstamp\*(C'\fR, which is what you should use too. It usually aliases +to the \f(CW\*(C`double\*(C'\fR type in C, and when you need to do any calculations on +it, you should treat it as some floatingpoint value. Unlike the name +component \f(CW\*(C`stamp\*(C'\fR might indicate, it is also used for time differences +throughout libev. +.SH "GLOBAL FUNCTIONS" +.IX Header "GLOBAL FUNCTIONS" +These functions can be called anytime, even before initialising the +library in any way. +.IP "ev_tstamp ev_time ()" 4 +.IX Item "ev_tstamp ev_time ()" +Returns the current time as libev would use it. Please note that the +\&\f(CW\*(C`ev_now\*(C'\fR function is usually faster and also often returns the timestamp +you actually want to know. +.IP "ev_sleep (ev_tstamp interval)" 4 +.IX Item "ev_sleep (ev_tstamp interval)" +Sleep for the given interval: The current thread will be blocked until +either it is interrupted or the given time interval has passed. Basically +this is a subsecond-resolution \f(CW\*(C`sleep ()\*(C'\fR. +.IP "int ev_version_major ()" 4 +.IX Item "int ev_version_major ()" +.PD 0 +.IP "int ev_version_minor ()" 4 +.IX Item "int ev_version_minor ()" +.PD +You can find out the major and minor \s-1ABI\s0 version numbers of the library +you linked against by calling the functions \f(CW\*(C`ev_version_major\*(C'\fR and +\&\f(CW\*(C`ev_version_minor\*(C'\fR. If you want, you can compare against the global +symbols \f(CW\*(C`EV_VERSION_MAJOR\*(C'\fR and \f(CW\*(C`EV_VERSION_MINOR\*(C'\fR, which specify the +version of the library your program was compiled against. +.Sp +These version numbers refer to the \s-1ABI\s0 version of the library, not the +release version. +.Sp +Usually, it's a good idea to terminate if the major versions mismatch, +as this indicates an incompatible change. Minor versions are usually +compatible to older versions, so a larger minor version alone is usually +not a problem. +.Sp +Example: Make sure we haven't accidentally been linked against the wrong +version. +.Sp +.Vb 3 +\& assert (("libev version mismatch", +\& ev_version_major () == EV_VERSION_MAJOR +\& && ev_version_minor () >= EV_VERSION_MINOR)); +.Ve +.IP "unsigned int ev_supported_backends ()" 4 +.IX Item "unsigned int ev_supported_backends ()" +Return the set of all backends (i.e. their corresponding \f(CW\*(C`EV_BACKEND_*\*(C'\fR +value) compiled into this binary of libev (independent of their +availability on the system you are running on). See \f(CW\*(C`ev_default_loop\*(C'\fR for +a description of the set values. +.Sp +Example: make sure we have the epoll method, because yeah this is cool and +a must have and can we have a torrent of it please!!!11 +.Sp +.Vb 2 +\& assert (("sorry, no epoll, no sex", +\& ev_supported_backends () & EVBACKEND_EPOLL)); +.Ve +.IP "unsigned int ev_recommended_backends ()" 4 +.IX Item "unsigned int ev_recommended_backends ()" +Return the set of all backends compiled into this binary of libev and also +recommended for this platform. This set is often smaller than the one +returned by \f(CW\*(C`ev_supported_backends\*(C'\fR, as for example kqueue is broken on +most BSDs and will not be autodetected unless you explicitly request it +(assuming you know what you are doing). This is the set of backends that +libev will probe for if you specify no backends explicitly. +.IP "unsigned int ev_embeddable_backends ()" 4 +.IX Item "unsigned int ev_embeddable_backends ()" +Returns the set of backends that are embeddable in other event loops. This +is the theoretical, all-platform, value. To find which backends +might be supported on the current system, you would need to look at +\&\f(CW\*(C`ev_embeddable_backends () & ev_supported_backends ()\*(C'\fR, likewise for +recommended ones. +.Sp +See the description of \f(CW\*(C`ev_embed\*(C'\fR watchers for more info. +.IP "ev_set_allocator (void *(*cb)(void *ptr, long size))" 4 +.IX Item "ev_set_allocator (void *(*cb)(void *ptr, long size))" +Sets the allocation function to use (the prototype is similar \- the +semantics are identical to the \f(CW\*(C`realloc\*(C'\fR C89/SuS/POSIX function). It is +used to allocate and free memory (no surprises here). If it returns zero +when memory needs to be allocated (\f(CW\*(C`size != 0\*(C'\fR), the library might abort +or take some potentially destructive action. +.Sp +Since some systems (at least OpenBSD and Darwin) fail to implement +correct \f(CW\*(C`realloc\*(C'\fR semantics, libev will use a wrapper around the system +\&\f(CW\*(C`realloc\*(C'\fR and \f(CW\*(C`free\*(C'\fR functions by default. +.Sp +You could override this function in high-availability programs to, say, +free some memory if it cannot allocate memory, to use a special allocator, +or even to sleep a while and retry until some memory is available. +.Sp +Example: Replace the libev allocator with one that waits a bit and then +retries (example requires a standards-compliant \f(CW\*(C`realloc\*(C'\fR). +.Sp +.Vb 6 +\& static void * +\& persistent_realloc (void *ptr, size_t size) +\& { +\& for (;;) +\& { +\& void *newptr = realloc (ptr, size); +\& +\& if (newptr) +\& return newptr; +\& +\& sleep (60); +\& } +\& } +\& +\& ... +\& ev_set_allocator (persistent_realloc); +.Ve +.IP "ev_set_syserr_cb (void (*cb)(const char *msg));" 4 +.IX Item "ev_set_syserr_cb (void (*cb)(const char *msg));" +Set the callback function to call on a retryable syscall error (such +as failed select, poll, epoll_wait). The message is a printable string +indicating the system call or subsystem causing the problem. If this +callback is set, then libev will expect it to remedy the sitution, no +matter what, when it returns. That is, libev will generally retry the +requested operation, or, if the condition doesn't go away, do bad stuff +(such as abort). +.Sp +Example: This is basically the same thing that libev does internally, too. +.Sp +.Vb 6 +\& static void +\& fatal_error (const char *msg) +\& { +\& perror (msg); +\& abort (); +\& } +\& +\& ... +\& ev_set_syserr_cb (fatal_error); +.Ve +.SH "FUNCTIONS CONTROLLING THE EVENT LOOP" +.IX Header "FUNCTIONS CONTROLLING THE EVENT LOOP" +An event loop is described by a \f(CW\*(C`struct ev_loop *\*(C'\fR. The library knows two +types of such loops, the \fIdefault\fR loop, which supports signals and child +events, and dynamically created loops which do not. +.IP "struct ev_loop *ev_default_loop (unsigned int flags)" 4 +.IX Item "struct ev_loop *ev_default_loop (unsigned int flags)" +This will initialise the default event loop if it hasn't been initialised +yet and return it. If the default loop could not be initialised, returns +false. If it already was initialised it simply returns it (and ignores the +flags. If that is troubling you, check \f(CW\*(C`ev_backend ()\*(C'\fR afterwards). +.Sp +If you don't know what event loop to use, use the one returned from this +function. +.Sp +Note that this function is \fInot\fR thread-safe, so if you want to use it +from multiple threads, you have to lock (note also that this is unlikely, +as loops cannot bes hared easily between threads anyway). +.Sp +The default loop is the only loop that can handle \f(CW\*(C`ev_signal\*(C'\fR and +\&\f(CW\*(C`ev_child\*(C'\fR watchers, and to do this, it always registers a handler +for \f(CW\*(C`SIGCHLD\*(C'\fR. If this is a problem for your app you can either +create a dynamic loop with \f(CW\*(C`ev_loop_new\*(C'\fR that doesn't do that, or you +can simply overwrite the \f(CW\*(C`SIGCHLD\*(C'\fR signal handler \fIafter\fR calling +\&\f(CW\*(C`ev_default_init\*(C'\fR. +.Sp +The flags argument can be used to specify special behaviour or specific +backends to use, and is usually specified as \f(CW0\fR (or \f(CW\*(C`EVFLAG_AUTO\*(C'\fR). +.Sp +The following flags are supported: +.RS 4 +.ie n .IP """EVFLAG_AUTO""" 4 +.el .IP "\f(CWEVFLAG_AUTO\fR" 4 +.IX Item "EVFLAG_AUTO" +The default flags value. Use this if you have no clue (it's the right +thing, believe me). +.ie n .IP """EVFLAG_NOENV""" 4 +.el .IP "\f(CWEVFLAG_NOENV\fR" 4 +.IX Item "EVFLAG_NOENV" +If this flag bit is ored into the flag value (or the program runs setuid +or setgid) then libev will \fInot\fR look at the environment variable +\&\f(CW\*(C`LIBEV_FLAGS\*(C'\fR. Otherwise (the default), this environment variable will +override the flags completely if it is found in the environment. This is +useful to try out specific backends to test their performance, or to work +around bugs. +.ie n .IP """EVFLAG_FORKCHECK""" 4 +.el .IP "\f(CWEVFLAG_FORKCHECK\fR" 4 +.IX Item "EVFLAG_FORKCHECK" +Instead of calling \f(CW\*(C`ev_default_fork\*(C'\fR or \f(CW\*(C`ev_loop_fork\*(C'\fR manually after +a fork, you can also make libev check for a fork in each iteration by +enabling this flag. +.Sp +This works by calling \f(CW\*(C`getpid ()\*(C'\fR on every iteration of the loop, +and thus this might slow down your event loop if you do a lot of loop +iterations and little real work, but is usually not noticeable (on my +GNU/Linux system for example, \f(CW\*(C`getpid\*(C'\fR is actually a simple 5\-insn sequence +without a syscall and thus \fIvery\fR fast, but my GNU/Linux system also has +\&\f(CW\*(C`pthread_atfork\*(C'\fR which is even faster). +.Sp +The big advantage of this flag is that you can forget about fork (and +forget about forgetting to tell libev about forking) when you use this +flag. +.Sp +This flag setting cannot be overriden or specified in the \f(CW\*(C`LIBEV_FLAGS\*(C'\fR +environment variable. +.ie n .IP """EVBACKEND_SELECT"" (value 1, portable select backend)" 4 +.el .IP "\f(CWEVBACKEND_SELECT\fR (value 1, portable select backend)" 4 +.IX Item "EVBACKEND_SELECT (value 1, portable select backend)" +This is your standard \fIselect\fR\|(2) backend. Not \fIcompletely\fR standard, as +libev tries to roll its own fd_set with no limits on the number of fds, +but if that fails, expect a fairly low limit on the number of fds when +using this backend. It doesn't scale too well (O(highest_fd)), but its +usually the fastest backend for a low number of (low-numbered :) fds. +.Sp +To get good performance out of this backend you need a high amount of +parallelity (most of the file descriptors should be busy). If you are +writing a server, you should \f(CW\*(C`accept ()\*(C'\fR in a loop to accept as many +connections as possible during one iteration. You might also want to have +a look at \f(CW\*(C`ev_set_io_collect_interval ()\*(C'\fR to increase the amount of +readyness notifications you get per iteration. +.ie n .IP """EVBACKEND_POLL"" (value 2, poll backend, available everywhere except on windows)" 4 +.el .IP "\f(CWEVBACKEND_POLL\fR (value 2, poll backend, available everywhere except on windows)" 4 +.IX Item "EVBACKEND_POLL (value 2, poll backend, available everywhere except on windows)" +And this is your standard \fIpoll\fR\|(2) backend. It's more complicated +than select, but handles sparse fds better and has no artificial +limit on the number of fds you can use (except it will slow down +considerably with a lot of inactive fds). It scales similarly to select, +i.e. O(total_fds). See the entry for \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR, above, for +performance tips. +.ie n .IP """EVBACKEND_EPOLL"" (value 4, Linux)" 4 +.el .IP "\f(CWEVBACKEND_EPOLL\fR (value 4, Linux)" 4 +.IX Item "EVBACKEND_EPOLL (value 4, Linux)" +For few fds, this backend is a bit little slower than poll and select, +but it scales phenomenally better. While poll and select usually scale +like O(total_fds) where n is the total number of fds (or the highest fd), +epoll scales either O(1) or O(active_fds). The epoll design has a number +of shortcomings, such as silently dropping events in some hard-to-detect +cases and requiring a syscall per fd change, no fork support and bad +support for dup. +.Sp +While stopping, setting and starting an I/O watcher in the same iteration +will result in some caching, there is still a syscall per such incident +(because the fd could point to a different file description now), so its +best to avoid that. Also, \f(CW\*(C`dup ()\*(C'\fR'ed file descriptors might not work +very well if you register events for both fds. +.Sp +Please note that epoll sometimes generates spurious notifications, so you +need to use non-blocking I/O or other means to avoid blocking when no data +(or space) is available. +.Sp +Best performance from this backend is achieved by not unregistering all +watchers for a file descriptor until it has been closed, if possible, i.e. +keep at least one watcher active per fd at all times. +.Sp +While nominally embeddeble in other event loops, this feature is broken in +all kernel versions tested so far. +.ie n .IP """EVBACKEND_KQUEUE"" (value 8, most \s-1BSD\s0 clones)" 4 +.el .IP "\f(CWEVBACKEND_KQUEUE\fR (value 8, most \s-1BSD\s0 clones)" 4 +.IX Item "EVBACKEND_KQUEUE (value 8, most BSD clones)" +Kqueue deserves special mention, as at the time of this writing, it +was broken on all BSDs except NetBSD (usually it doesn't work reliably +with anything but sockets and pipes, except on Darwin, where of course +it's completely useless). For this reason it's not being \*(L"autodetected\*(R" +unless you explicitly specify it explicitly in the flags (i.e. using +\&\f(CW\*(C`EVBACKEND_KQUEUE\*(C'\fR) or libev was compiled on a known-to-be-good (\-enough) +system like NetBSD. +.Sp +You still can embed kqueue into a normal poll or select backend and use it +only for sockets (after having made sure that sockets work with kqueue on +the target platform). See \f(CW\*(C`ev_embed\*(C'\fR watchers for more info. +.Sp +It scales in the same way as the epoll backend, but the interface to the +kernel is more efficient (which says nothing about its actual speed, of +course). While stopping, setting and starting an I/O watcher does never +cause an extra syscall as with \f(CW\*(C`EVBACKEND_EPOLL\*(C'\fR, it still adds up to +two event changes per incident, support for \f(CW\*(C`fork ()\*(C'\fR is very bad and it +drops fds silently in similarly hard-to-detect cases. +.Sp +This backend usually performs well under most conditions. +.Sp +While nominally embeddable in other event loops, this doesn't work +everywhere, so you might need to test for this. And since it is broken +almost everywhere, you should only use it when you have a lot of sockets +(for which it usually works), by embedding it into another event loop +(e.g. \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR or \f(CW\*(C`EVBACKEND_POLL\*(C'\fR) and using it only for +sockets. +.ie n .IP """EVBACKEND_DEVPOLL"" (value 16, Solaris 8)" 4 +.el .IP "\f(CWEVBACKEND_DEVPOLL\fR (value 16, Solaris 8)" 4 +.IX Item "EVBACKEND_DEVPOLL (value 16, Solaris 8)" +This is not implemented yet (and might never be, unless you send me an +implementation). According to reports, \f(CW\*(C`/dev/poll\*(C'\fR only supports sockets +and is not embeddable, which would limit the usefulness of this backend +immensely. +.ie n .IP """EVBACKEND_PORT"" (value 32, Solaris 10)" 4 +.el .IP "\f(CWEVBACKEND_PORT\fR (value 32, Solaris 10)" 4 +.IX Item "EVBACKEND_PORT (value 32, Solaris 10)" +This uses the Solaris 10 event port mechanism. As with everything on Solaris, +it's really slow, but it still scales very well (O(active_fds)). +.Sp +Please note that solaris event ports can deliver a lot of spurious +notifications, so you need to use non-blocking I/O or other means to avoid +blocking when no data (or space) is available. +.Sp +While this backend scales well, it requires one system call per active +file descriptor per loop iteration. For small and medium numbers of file +descriptors a \*(L"slow\*(R" \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR or \f(CW\*(C`EVBACKEND_POLL\*(C'\fR backend +might perform better. +.Sp +On the positive side, ignoring the spurious readyness notifications, this +backend actually performed to specification in all tests and is fully +embeddable, which is a rare feat among the OS-specific backends. +.ie n .IP """EVBACKEND_ALL""" 4 +.el .IP "\f(CWEVBACKEND_ALL\fR" 4 +.IX Item "EVBACKEND_ALL" +Try all backends (even potentially broken ones that wouldn't be tried +with \f(CW\*(C`EVFLAG_AUTO\*(C'\fR). Since this is a mask, you can do stuff such as +\&\f(CW\*(C`EVBACKEND_ALL & ~EVBACKEND_KQUEUE\*(C'\fR. +.Sp +It is definitely not recommended to use this flag. +.RE +.RS 4 +.Sp +If one or more of these are ored into the flags value, then only these +backends will be tried (in the reverse order as listed here). If none are +specified, all backends in \f(CW\*(C`ev_recommended_backends ()\*(C'\fR will be tried. +.Sp +The most typical usage is like this: +.Sp +.Vb 2 +\& if (!ev_default_loop (0)) +\& fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?"); +.Ve +.Sp +Restrict libev to the select and poll backends, and do not allow +environment settings to be taken into account: +.Sp +.Vb 1 +\& ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV); +.Ve +.Sp +Use whatever libev has to offer, but make sure that kqueue is used if +available (warning, breaks stuff, best use only with your own private +event loop and only if you know the \s-1OS\s0 supports your types of fds): +.Sp +.Vb 1 +\& ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE); +.Ve +.RE +.IP "struct ev_loop *ev_loop_new (unsigned int flags)" 4 +.IX Item "struct ev_loop *ev_loop_new (unsigned int flags)" +Similar to \f(CW\*(C`ev_default_loop\*(C'\fR, but always creates a new event loop that is +always distinct from the default loop. Unlike the default loop, it cannot +handle signal and child watchers, and attempts to do so will be greeted by +undefined behaviour (or a failed assertion if assertions are enabled). +.Sp +Note that this function \fIis\fR thread-safe, and the recommended way to use +libev with threads is indeed to create one loop per thread, and using the +default loop in the \*(L"main\*(R" or \*(L"initial\*(R" thread. +.Sp +Example: Try to create a event loop that uses epoll and nothing else. +.Sp +.Vb 3 +\& struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV); +\& if (!epoller) +\& fatal ("no epoll found here, maybe it hides under your chair"); +.Ve +.IP "ev_default_destroy ()" 4 +.IX Item "ev_default_destroy ()" +Destroys the default loop again (frees all memory and kernel state +etc.). None of the active event watchers will be stopped in the normal +sense, so e.g. \f(CW\*(C`ev_is_active\*(C'\fR might still return true. It is your +responsibility to either stop all watchers cleanly yoursef \fIbefore\fR +calling this function, or cope with the fact afterwards (which is usually +the easiest thing, you can just ignore the watchers and/or \f(CW\*(C`free ()\*(C'\fR them +for example). +.Sp +Note that certain global state, such as signal state, will not be freed by +this function, and related watchers (such as signal and child watchers) +would need to be stopped manually. +.Sp +In general it is not advisable to call this function except in the +rare occasion where you really need to free e.g. the signal handling +pipe fds. If you need dynamically allocated loops it is better to use +\&\f(CW\*(C`ev_loop_new\*(C'\fR and \f(CW\*(C`ev_loop_destroy\*(C'\fR). +.IP "ev_loop_destroy (loop)" 4 +.IX Item "ev_loop_destroy (loop)" +Like \f(CW\*(C`ev_default_destroy\*(C'\fR, but destroys an event loop created by an +earlier call to \f(CW\*(C`ev_loop_new\*(C'\fR. +.IP "ev_default_fork ()" 4 +.IX Item "ev_default_fork ()" +This function sets a flag that causes subsequent \f(CW\*(C`ev_loop\*(C'\fR iterations +to reinitialise the kernel state for backends that have one. Despite the +name, you can call it anytime, but it makes most sense after forking, in +the child process (or both child and parent, but that again makes little +sense). You \fImust\fR call it in the child before using any of the libev +functions, and it will only take effect at the next \f(CW\*(C`ev_loop\*(C'\fR iteration. +.Sp +On the other hand, you only need to call this function in the child +process if and only if you want to use the event library in the child. If +you just fork+exec, you don't have to call it at all. +.Sp +The function itself is quite fast and it's usually not a problem to call +it just in case after a fork. To make this easy, the function will fit in +quite nicely into a call to \f(CW\*(C`pthread_atfork\*(C'\fR: +.Sp +.Vb 1 +\& pthread_atfork (0, 0, ev_default_fork); +.Ve +.IP "ev_loop_fork (loop)" 4 +.IX Item "ev_loop_fork (loop)" +Like \f(CW\*(C`ev_default_fork\*(C'\fR, but acts on an event loop created by +\&\f(CW\*(C`ev_loop_new\*(C'\fR. Yes, you have to call this on every allocated event loop +after fork, and how you do this is entirely your own problem. +.IP "int ev_is_default_loop (loop)" 4 +.IX Item "int ev_is_default_loop (loop)" +Returns true when the given loop actually is the default loop, false otherwise. +.IP "unsigned int ev_loop_count (loop)" 4 +.IX Item "unsigned int ev_loop_count (loop)" +Returns the count of loop iterations for the loop, which is identical to +the number of times libev did poll for new events. It starts at \f(CW0\fR and +happily wraps around with enough iterations. +.Sp +This value can sometimes be useful as a generation counter of sorts (it +\&\*(L"ticks\*(R" the number of loop iterations), as it roughly corresponds with +\&\f(CW\*(C`ev_prepare\*(C'\fR and \f(CW\*(C`ev_check\*(C'\fR calls. +.IP "unsigned int ev_backend (loop)" 4 +.IX Item "unsigned int ev_backend (loop)" +Returns one of the \f(CW\*(C`EVBACKEND_*\*(C'\fR flags indicating the event backend in +use. +.IP "ev_tstamp ev_now (loop)" 4 +.IX Item "ev_tstamp ev_now (loop)" +Returns the current \*(L"event loop time\*(R", which is the time the event loop +received events and started processing them. This timestamp does not +change as long as callbacks are being processed, and this is also the base +time used for relative timers. You can treat it as the timestamp of the +event occurring (or more correctly, libev finding out about it). +.IP "ev_loop (loop, int flags)" 4 +.IX Item "ev_loop (loop, int flags)" +Finally, this is it, the event handler. This function usually is called +after you initialised all your watchers and you want to start handling +events. +.Sp +If the flags argument is specified as \f(CW0\fR, it will not return until +either no event watchers are active anymore or \f(CW\*(C`ev_unloop\*(C'\fR was called. +.Sp +Please note that an explicit \f(CW\*(C`ev_unloop\*(C'\fR is usually better than +relying on all watchers to be stopped when deciding when a program has +finished (especially in interactive programs), but having a program that +automatically loops as long as it has to and no longer by virtue of +relying on its watchers stopping correctly is a thing of beauty. +.Sp +A flags value of \f(CW\*(C`EVLOOP_NONBLOCK\*(C'\fR will look for new events, will handle +those events and any outstanding ones, but will not block your process in +case there are no events and will return after one iteration of the loop. +.Sp +A flags value of \f(CW\*(C`EVLOOP_ONESHOT\*(C'\fR will look for new events (waiting if +neccessary) and will handle those and any outstanding ones. It will block +your process until at least one new event arrives, and will return after +one iteration of the loop. This is useful if you are waiting for some +external event in conjunction with something not expressible using other +libev watchers. However, a pair of \f(CW\*(C`ev_prepare\*(C'\fR/\f(CW\*(C`ev_check\*(C'\fR watchers is +usually a better approach for this kind of thing. +.Sp +Here are the gory details of what \f(CW\*(C`ev_loop\*(C'\fR does: +.Sp +.Vb 10 +\& \- Before the first iteration, call any pending watchers. +\& * If EVFLAG_FORKCHECK was used, check for a fork. +\& \- If a fork was detected, queue and call all fork watchers. +\& \- Queue and call all prepare watchers. +\& \- If we have been forked, recreate the kernel state. +\& \- Update the kernel state with all outstanding changes. +\& \- Update the "event loop time". +\& \- Calculate for how long to sleep or block, if at all +\& (active idle watchers, EVLOOP_NONBLOCK or not having +\& any active watchers at all will result in not sleeping). +\& \- Sleep if the I/O and timer collect interval say so. +\& \- Block the process, waiting for any events. +\& \- Queue all outstanding I/O (fd) events. +\& \- Update the "event loop time" and do time jump handling. +\& \- Queue all outstanding timers. +\& \- Queue all outstanding periodics. +\& \- If no events are pending now, queue all idle watchers. +\& \- Queue all check watchers. +\& \- Call all queued watchers in reverse order (i.e. check watchers first). +\& Signals and child watchers are implemented as I/O watchers, and will +\& be handled here by queueing them when their watcher gets executed. +\& \- If ev_unloop has been called, or EVLOOP_ONESHOT or EVLOOP_NONBLOCK +\& were used, or there are no active watchers, return, otherwise +\& continue with step *. +.Ve +.Sp +Example: Queue some jobs and then loop until no events are outstanding +anymore. +.Sp +.Vb 4 +\& ... queue jobs here, make sure they register event watchers as long +\& ... as they still have work to do (even an idle watcher will do..) +\& ev_loop (my_loop, 0); +\& ... jobs done. yeah! +.Ve +.IP "ev_unloop (loop, how)" 4 +.IX Item "ev_unloop (loop, how)" +Can be used to make a call to \f(CW\*(C`ev_loop\*(C'\fR return early (but only after it +has processed all outstanding events). The \f(CW\*(C`how\*(C'\fR argument must be either +\&\f(CW\*(C`EVUNLOOP_ONE\*(C'\fR, which will make the innermost \f(CW\*(C`ev_loop\*(C'\fR call return, or +\&\f(CW\*(C`EVUNLOOP_ALL\*(C'\fR, which will make all nested \f(CW\*(C`ev_loop\*(C'\fR calls return. +.Sp +This \*(L"unloop state\*(R" will be cleared when entering \f(CW\*(C`ev_loop\*(C'\fR again. +.IP "ev_ref (loop)" 4 +.IX Item "ev_ref (loop)" +.PD 0 +.IP "ev_unref (loop)" 4 +.IX Item "ev_unref (loop)" +.PD +Ref/unref can be used to add or remove a reference count on the event +loop: Every watcher keeps one reference, and as long as the reference +count is nonzero, \f(CW\*(C`ev_loop\*(C'\fR will not return on its own. If you have +a watcher you never unregister that should not keep \f(CW\*(C`ev_loop\*(C'\fR from +returning, \fIev_unref()\fR after starting, and \fIev_ref()\fR before stopping it. For +example, libev itself uses this for its internal signal pipe: It is not +visible to the libev user and should not keep \f(CW\*(C`ev_loop\*(C'\fR from exiting if +no event watchers registered by it are active. It is also an excellent +way to do this for generic recurring timers or from within third-party +libraries. Just remember to \fIunref after start\fR and \fIref before stop\fR +(but only if the watcher wasn't active before, or was active before, +respectively). +.Sp +Example: Create a signal watcher, but keep it from keeping \f(CW\*(C`ev_loop\*(C'\fR +running when nothing else is active. +.Sp +.Vb 4 +\& struct ev_signal exitsig; +\& ev_signal_init (&exitsig, sig_cb, SIGINT); +\& ev_signal_start (loop, &exitsig); +\& evf_unref (loop); +.Ve +.Sp +Example: For some weird reason, unregister the above signal handler again. +.Sp +.Vb 2 +\& ev_ref (loop); +\& ev_signal_stop (loop, &exitsig); +.Ve +.IP "ev_set_io_collect_interval (loop, ev_tstamp interval)" 4 +.IX Item "ev_set_io_collect_interval (loop, ev_tstamp interval)" +.PD 0 +.IP "ev_set_timeout_collect_interval (loop, ev_tstamp interval)" 4 +.IX Item "ev_set_timeout_collect_interval (loop, ev_tstamp interval)" +.PD +These advanced functions influence the time that libev will spend waiting +for events. Both are by default \f(CW0\fR, meaning that libev will try to +invoke timer/periodic callbacks and I/O callbacks with minimum latency. +.Sp +Setting these to a higher value (the \f(CW\*(C`interval\*(C'\fR \fImust\fR be >= \f(CW0\fR) +allows libev to delay invocation of I/O and timer/periodic callbacks to +increase efficiency of loop iterations. +.Sp +The background is that sometimes your program runs just fast enough to +handle one (or very few) event(s) per loop iteration. While this makes +the program responsive, it also wastes a lot of \s-1CPU\s0 time to poll for new +events, especially with backends like \f(CW\*(C`select ()\*(C'\fR which have a high +overhead for the actual polling but can deliver many events at once. +.Sp +By setting a higher \fIio collect interval\fR you allow libev to spend more +time collecting I/O events, so you can handle more events per iteration, +at the cost of increasing latency. Timeouts (both \f(CW\*(C`ev_periodic\*(C'\fR and +\&\f(CW\*(C`ev_timer\*(C'\fR) will be not affected. Setting this to a non-null value will +introduce an additional \f(CW\*(C`ev_sleep ()\*(C'\fR call into most loop iterations. +.Sp +Likewise, by setting a higher \fItimeout collect interval\fR you allow libev +to spend more time collecting timeouts, at the expense of increased +latency (the watcher callback will be called later). \f(CW\*(C`ev_io\*(C'\fR watchers +will not be affected. Setting this to a non-null value will not introduce +any overhead in libev. +.Sp +Many (busy) programs can usually benefit by setting the io collect +interval to a value near \f(CW0.1\fR or so, which is often enough for +interactive servers (of course not for games), likewise for timeouts. It +usually doesn't make much sense to set it to a lower value than \f(CW0.01\fR, +as this approsaches the timing granularity of most systems. +.SH "ANATOMY OF A WATCHER" +.IX Header "ANATOMY OF A WATCHER" +A watcher is a structure that you create and register to record your +interest in some event. For instance, if you want to wait for \s-1STDIN\s0 to +become readable, you would create an \f(CW\*(C`ev_io\*(C'\fR watcher for that: +.PP +.Vb 5 +\& static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents) +\& { +\& ev_io_stop (w); +\& ev_unloop (loop, EVUNLOOP_ALL); +\& } +\& +\& struct ev_loop *loop = ev_default_loop (0); +\& struct ev_io stdin_watcher; +\& ev_init (&stdin_watcher, my_cb); +\& ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ); +\& ev_io_start (loop, &stdin_watcher); +\& ev_loop (loop, 0); +.Ve +.PP +As you can see, you are responsible for allocating the memory for your +watcher structures (and it is usually a bad idea to do this on the stack, +although this can sometimes be quite valid). +.PP +Each watcher structure must be initialised by a call to \f(CW\*(C`ev_init +(watcher *, callback)\*(C'\fR, which expects a callback to be provided. This +callback gets invoked each time the event occurs (or, in the case of io +watchers, each time the event loop detects that the file descriptor given +is readable and/or writable). +.PP +Each watcher type has its own \f(CW\*(C`ev_<type>_set (watcher *, ...)\*(C'\fR macro +with arguments specific to this watcher type. There is also a macro +to combine initialisation and setting in one call: \f(CW\*(C`ev_<type>_init +(watcher *, callback, ...)\*(C'\fR. +.PP +To make the watcher actually watch out for events, you have to start it +with a watcher-specific start function (\f(CW\*(C`ev_<type>_start (loop, watcher +*)\*(C'\fR), and you can stop watching for events at any time by calling the +corresponding stop function (\f(CW\*(C`ev_<type>_stop (loop, watcher *)\*(C'\fR. +.PP +As long as your watcher is active (has been started but not stopped) you +must not touch the values stored in it. Most specifically you must never +reinitialise it or call its \f(CW\*(C`set\*(C'\fR macro. +.PP +Each and every callback receives the event loop pointer as first, the +registered watcher structure as second, and a bitset of received events as +third argument. +.PP +The received events usually include a single bit per event type received +(you can receive multiple events at the same time). The possible bit masks +are: +.ie n .IP """EV_READ""" 4 +.el .IP "\f(CWEV_READ\fR" 4 +.IX Item "EV_READ" +.PD 0 +.ie n .IP """EV_WRITE""" 4 +.el .IP "\f(CWEV_WRITE\fR" 4 +.IX Item "EV_WRITE" +.PD +The file descriptor in the \f(CW\*(C`ev_io\*(C'\fR watcher has become readable and/or +writable. +.ie n .IP """EV_TIMEOUT""" 4 +.el .IP "\f(CWEV_TIMEOUT\fR" 4 +.IX Item "EV_TIMEOUT" +The \f(CW\*(C`ev_timer\*(C'\fR watcher has timed out. +.ie n .IP """EV_PERIODIC""" 4 +.el .IP "\f(CWEV_PERIODIC\fR" 4 +.IX Item "EV_PERIODIC" +The \f(CW\*(C`ev_periodic\*(C'\fR watcher has timed out. +.ie n .IP """EV_SIGNAL""" 4 +.el .IP "\f(CWEV_SIGNAL\fR" 4 +.IX Item "EV_SIGNAL" +The signal specified in the \f(CW\*(C`ev_signal\*(C'\fR watcher has been received by a thread. +.ie n .IP """EV_CHILD""" 4 +.el .IP "\f(CWEV_CHILD\fR" 4 +.IX Item "EV_CHILD" +The pid specified in the \f(CW\*(C`ev_child\*(C'\fR watcher has received a status change. +.ie n .IP """EV_STAT""" 4 +.el .IP "\f(CWEV_STAT\fR" 4 +.IX Item "EV_STAT" +The path specified in the \f(CW\*(C`ev_stat\*(C'\fR watcher changed its attributes somehow. +.ie n .IP """EV_IDLE""" 4 +.el .IP "\f(CWEV_IDLE\fR" 4 +.IX Item "EV_IDLE" +The \f(CW\*(C`ev_idle\*(C'\fR watcher has determined that you have nothing better to do. +.ie n .IP """EV_PREPARE""" 4 +.el .IP "\f(CWEV_PREPARE\fR" 4 +.IX Item "EV_PREPARE" +.PD 0 +.ie n .IP """EV_CHECK""" 4 +.el .IP "\f(CWEV_CHECK\fR" 4 +.IX Item "EV_CHECK" +.PD +All \f(CW\*(C`ev_prepare\*(C'\fR watchers are invoked just \fIbefore\fR \f(CW\*(C`ev_loop\*(C'\fR starts +to gather new events, and all \f(CW\*(C`ev_check\*(C'\fR watchers are invoked just after +\&\f(CW\*(C`ev_loop\*(C'\fR has gathered them, but before it invokes any callbacks for any +received events. Callbacks of both watcher types can start and stop as +many watchers as they want, and all of them will be taken into account +(for example, a \f(CW\*(C`ev_prepare\*(C'\fR watcher might start an idle watcher to keep +\&\f(CW\*(C`ev_loop\*(C'\fR from blocking). +.ie n .IP """EV_EMBED""" 4 +.el .IP "\f(CWEV_EMBED\fR" 4 +.IX Item "EV_EMBED" +The embedded event loop specified in the \f(CW\*(C`ev_embed\*(C'\fR watcher needs attention. +.ie n .IP """EV_FORK""" 4 +.el .IP "\f(CWEV_FORK\fR" 4 +.IX Item "EV_FORK" +The event loop has been resumed in the child process after fork (see +\&\f(CW\*(C`ev_fork\*(C'\fR). +.ie n .IP """EV_ASYNC""" 4 +.el .IP "\f(CWEV_ASYNC\fR" 4 +.IX Item "EV_ASYNC" +The given async watcher has been asynchronously notified (see \f(CW\*(C`ev_async\*(C'\fR). +.ie n .IP """EV_ERROR""" 4 +.el .IP "\f(CWEV_ERROR\fR" 4 +.IX Item "EV_ERROR" +An unspecified error has occured, the watcher has been stopped. This might +happen because the watcher could not be properly started because libev +ran out of memory, a file descriptor was found to be closed or any other +problem. You best act on it by reporting the problem and somehow coping +with the watcher being stopped. +.Sp +Libev will usually signal a few \*(L"dummy\*(R" events together with an error, +for example it might indicate that a fd is readable or writable, and if +your callbacks is well-written it can just attempt the operation and cope +with the error from \fIread()\fR or \fIwrite()\fR. This will not work in multithreaded +programs, though, so beware. +.Sh "\s-1GENERIC\s0 \s-1WATCHER\s0 \s-1FUNCTIONS\s0" +.IX Subsection "GENERIC WATCHER FUNCTIONS" +In the following description, \f(CW\*(C`TYPE\*(C'\fR stands for the watcher type, +e.g. \f(CW\*(C`timer\*(C'\fR for \f(CW\*(C`ev_timer\*(C'\fR watchers and \f(CW\*(C`io\*(C'\fR for \f(CW\*(C`ev_io\*(C'\fR watchers. +.ie n .IP """ev_init"" (ev_TYPE *watcher, callback)" 4 +.el .IP "\f(CWev_init\fR (ev_TYPE *watcher, callback)" 4 +.IX Item "ev_init (ev_TYPE *watcher, callback)" +This macro initialises the generic portion of a watcher. The contents +of the watcher object can be arbitrary (so \f(CW\*(C`malloc\*(C'\fR will do). Only +the generic parts of the watcher are initialised, you \fIneed\fR to call +the type-specific \f(CW\*(C`ev_TYPE_set\*(C'\fR macro afterwards to initialise the +type-specific parts. For each type there is also a \f(CW\*(C`ev_TYPE_init\*(C'\fR macro +which rolls both calls into one. +.Sp +You can reinitialise a watcher at any time as long as it has been stopped +(or never started) and there are no pending events outstanding. +.Sp +The callback is always of type \f(CW\*(C`void (*)(ev_loop *loop, ev_TYPE *watcher, +int revents)\*(C'\fR. +.ie n .IP """ev_TYPE_set"" (ev_TYPE *, [args])" 4 +.el .IP "\f(CWev_TYPE_set\fR (ev_TYPE *, [args])" 4 +.IX Item "ev_TYPE_set (ev_TYPE *, [args])" +This macro initialises the type-specific parts of a watcher. You need to +call \f(CW\*(C`ev_init\*(C'\fR at least once before you call this macro, but you can +call \f(CW\*(C`ev_TYPE_set\*(C'\fR any number of times. You must not, however, call this +macro on a watcher that is active (it can be pending, however, which is a +difference to the \f(CW\*(C`ev_init\*(C'\fR macro). +.Sp +Although some watcher types do not have type-specific arguments +(e.g. \f(CW\*(C`ev_prepare\*(C'\fR) you still need to call its \f(CW\*(C`set\*(C'\fR macro. +.ie n .IP """ev_TYPE_init"" (ev_TYPE *watcher, callback, [args])" 4 +.el .IP "\f(CWev_TYPE_init\fR (ev_TYPE *watcher, callback, [args])" 4 +.IX Item "ev_TYPE_init (ev_TYPE *watcher, callback, [args])" +This convinience macro rolls both \f(CW\*(C`ev_init\*(C'\fR and \f(CW\*(C`ev_TYPE_set\*(C'\fR macro +calls into a single call. This is the most convinient method to initialise +a watcher. The same limitations apply, of course. +.ie n .IP """ev_TYPE_start"" (loop *, ev_TYPE *watcher)" 4 +.el .IP "\f(CWev_TYPE_start\fR (loop *, ev_TYPE *watcher)" 4 +.IX Item "ev_TYPE_start (loop *, ev_TYPE *watcher)" +Starts (activates) the given watcher. Only active watchers will receive +events. If the watcher is already active nothing will happen. +.ie n .IP """ev_TYPE_stop"" (loop *, ev_TYPE *watcher)" 4 +.el .IP "\f(CWev_TYPE_stop\fR (loop *, ev_TYPE *watcher)" 4 +.IX Item "ev_TYPE_stop (loop *, ev_TYPE *watcher)" +Stops the given watcher again (if active) and clears the pending +status. It is possible that stopped watchers are pending (for example, +non-repeating timers are being stopped when they become pending), but +\&\f(CW\*(C`ev_TYPE_stop\*(C'\fR ensures that the watcher is neither active nor pending. If +you want to free or reuse the memory used by the watcher it is therefore a +good idea to always call its \f(CW\*(C`ev_TYPE_stop\*(C'\fR function. +.IP "bool ev_is_active (ev_TYPE *watcher)" 4 +.IX Item "bool ev_is_active (ev_TYPE *watcher)" +Returns a true value iff the watcher is active (i.e. it has been started +and not yet been stopped). As long as a watcher is active you must not modify +it. +.IP "bool ev_is_pending (ev_TYPE *watcher)" 4 +.IX Item "bool ev_is_pending (ev_TYPE *watcher)" +Returns a true value iff the watcher is pending, (i.e. it has outstanding +events but its callback has not yet been invoked). As long as a watcher +is pending (but not active) you must not call an init function on it (but +\&\f(CW\*(C`ev_TYPE_set\*(C'\fR is safe), you must not change its priority, and you must +make sure the watcher is available to libev (e.g. you cannot \f(CW\*(C`free ()\*(C'\fR +it). +.IP "callback ev_cb (ev_TYPE *watcher)" 4 +.IX Item "callback ev_cb (ev_TYPE *watcher)" +Returns the callback currently set on the watcher. +.IP "ev_cb_set (ev_TYPE *watcher, callback)" 4 +.IX Item "ev_cb_set (ev_TYPE *watcher, callback)" +Change the callback. You can change the callback at virtually any time +(modulo threads). +.IP "ev_set_priority (ev_TYPE *watcher, priority)" 4 +.IX Item "ev_set_priority (ev_TYPE *watcher, priority)" +.PD 0 +.IP "int ev_priority (ev_TYPE *watcher)" 4 +.IX Item "int ev_priority (ev_TYPE *watcher)" +.PD +Set and query the priority of the watcher. The priority is a small +integer between \f(CW\*(C`EV_MAXPRI\*(C'\fR (default: \f(CW2\fR) and \f(CW\*(C`EV_MINPRI\*(C'\fR +(default: \f(CW\*(C`\-2\*(C'\fR). Pending watchers with higher priority will be invoked +before watchers with lower priority, but priority will not keep watchers +from being executed (except for \f(CW\*(C`ev_idle\*(C'\fR watchers). +.Sp +This means that priorities are \fIonly\fR used for ordering callback +invocation after new events have been received. This is useful, for +example, to reduce latency after idling, or more often, to bind two +watchers on the same event and make sure one is called first. +.Sp +If you need to suppress invocation when higher priority events are pending +you need to look at \f(CW\*(C`ev_idle\*(C'\fR watchers, which provide this functionality. +.Sp +You \fImust not\fR change the priority of a watcher as long as it is active or +pending. +.Sp +The default priority used by watchers when no priority has been set is +always \f(CW0\fR, which is supposed to not be too high and not be too low :). +.Sp +Setting a priority outside the range of \f(CW\*(C`EV_MINPRI\*(C'\fR to \f(CW\*(C`EV_MAXPRI\*(C'\fR is +fine, as long as you do not mind that the priority value you query might +or might not have been adjusted to be within valid range. +.IP "ev_invoke (loop, ev_TYPE *watcher, int revents)" 4 +.IX Item "ev_invoke (loop, ev_TYPE *watcher, int revents)" +Invoke the \f(CW\*(C`watcher\*(C'\fR with the given \f(CW\*(C`loop\*(C'\fR and \f(CW\*(C`revents\*(C'\fR. Neither +\&\f(CW\*(C`loop\*(C'\fR nor \f(CW\*(C`revents\*(C'\fR need to be valid as long as the watcher callback +can deal with that fact. +.IP "int ev_clear_pending (loop, ev_TYPE *watcher)" 4 +.IX Item "int ev_clear_pending (loop, ev_TYPE *watcher)" +If the watcher is pending, this function returns clears its pending status +and returns its \f(CW\*(C`revents\*(C'\fR bitset (as if its callback was invoked). If the +watcher isn't pending it does nothing and returns \f(CW0\fR. +.Sh "\s-1ASSOCIATING\s0 \s-1CUSTOM\s0 \s-1DATA\s0 \s-1WITH\s0 A \s-1WATCHER\s0" +.IX Subsection "ASSOCIATING CUSTOM DATA WITH A WATCHER" +Each watcher has, by default, a member \f(CW\*(C`void *data\*(C'\fR that you can change +and read at any time, libev will completely ignore it. This can be used +to associate arbitrary data with your watcher. If you need more data and +don't want to allocate memory and store a pointer to it in that data +member, you can also \*(L"subclass\*(R" the watcher type and provide your own +data: +.PP +.Vb 7 +\& struct my_io +\& { +\& struct ev_io io; +\& int otherfd; +\& void *somedata; +\& struct whatever *mostinteresting; +\& } +.Ve +.PP +And since your callback will be called with a pointer to the watcher, you +can cast it back to your own type: +.PP +.Vb 5 +\& static void my_cb (struct ev_loop *loop, struct ev_io *w_, int revents) +\& { +\& struct my_io *w = (struct my_io *)w_; +\& ... +\& } +.Ve +.PP +More interesting and less C\-conformant ways of casting your callback type +instead have been omitted. +.PP +Another common scenario is having some data structure with multiple +watchers: +.PP +.Vb 6 +\& struct my_biggy +\& { +\& int some_data; +\& ev_timer t1; +\& ev_timer t2; +\& } +.Ve +.PP +In this case getting the pointer to \f(CW\*(C`my_biggy\*(C'\fR is a bit more complicated, +you need to use \f(CW\*(C`offsetof\*(C'\fR: +.PP +.Vb 1 +\& #include <stddef.h> +\& +\& static void +\& t1_cb (EV_P_ struct ev_timer *w, int revents) +\& { +\& struct my_biggy big = (struct my_biggy * +\& (((char *)w) \- offsetof (struct my_biggy, t1)); +\& } +\& +\& static void +\& t2_cb (EV_P_ struct ev_timer *w, int revents) +\& { +\& struct my_biggy big = (struct my_biggy * +\& (((char *)w) \- offsetof (struct my_biggy, t2)); +\& } +.Ve +.SH "WATCHER TYPES" +.IX Header "WATCHER TYPES" +This section describes each watcher in detail, but will not repeat +information given in the last section. Any initialisation/set macros, +functions and members specific to the watcher type are explained. +.PP +Members are additionally marked with either \fI[read\-only]\fR, meaning that, +while the watcher is active, you can look at the member and expect some +sensible content, but you must not modify it (you can modify it while the +watcher is stopped to your hearts content), or \fI[read\-write]\fR, which +means you can expect it to have some sensible content while the watcher +is active, but you can also modify it. Modifying it may not do something +sensible or take immediate effect (or do anything at all), but libev will +not crash or malfunction in any way. +.ie n .Sh """ev_io"" \- is this file descriptor readable or writable?" +.el .Sh "\f(CWev_io\fP \- is this file descriptor readable or writable?" +.IX Subsection "ev_io - is this file descriptor readable or writable?" +I/O watchers check whether a file descriptor is readable or writable +in each iteration of the event loop, or, more precisely, when reading +would not block the process and writing would at least be able to write +some data. This behaviour is called level-triggering because you keep +receiving events as long as the condition persists. Remember you can stop +the watcher if you don't want to act on the event and neither want to +receive future events. +.PP +In general you can register as many read and/or write event watchers per +fd as you want (as long as you don't confuse yourself). Setting all file +descriptors to non-blocking mode is also usually a good idea (but not +required if you know what you are doing). +.PP +If you must do this, then force the use of a known-to-be-good backend +(at the time of this writing, this includes only \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR and +\&\f(CW\*(C`EVBACKEND_POLL\*(C'\fR). +.PP +Another thing you have to watch out for is that it is quite easy to +receive \*(L"spurious\*(R" readyness notifications, that is your callback might +be called with \f(CW\*(C`EV_READ\*(C'\fR but a subsequent \f(CW\*(C`read\*(C'\fR(2) will actually block +because there is no data. Not only are some backends known to create a +lot of those (for example solaris ports), it is very easy to get into +this situation even with a relatively standard program structure. Thus +it is best to always use non-blocking I/O: An extra \f(CW\*(C`read\*(C'\fR(2) returning +\&\f(CW\*(C`EAGAIN\*(C'\fR is far preferable to a program hanging until some data arrives. +.PP +If you cannot run the fd in non-blocking mode (for example you should not +play around with an Xlib connection), then you have to seperately re-test +whether a file descriptor is really ready with a known-to-be good interface +such as poll (fortunately in our Xlib example, Xlib already does this on +its own, so its quite safe to use). +.PP +\fIThe special problem of disappearing file descriptors\fR +.IX Subsection "The special problem of disappearing file descriptors" +.PP +Some backends (e.g. kqueue, epoll) need to be told about closing a file +descriptor (either by calling \f(CW\*(C`close\*(C'\fR explicitly or by any other means, +such as \f(CW\*(C`dup\*(C'\fR). The reason is that you register interest in some file +descriptor, but when it goes away, the operating system will silently drop +this interest. If another file descriptor with the same number then is +registered with libev, there is no efficient way to see that this is, in +fact, a different file descriptor. +.PP +To avoid having to explicitly tell libev about such cases, libev follows +the following policy: Each time \f(CW\*(C`ev_io_set\*(C'\fR is being called, libev +will assume that this is potentially a new file descriptor, otherwise +it is assumed that the file descriptor stays the same. That means that +you \fIhave\fR to call \f(CW\*(C`ev_io_set\*(C'\fR (or \f(CW\*(C`ev_io_init\*(C'\fR) when you change the +descriptor even if the file descriptor number itself did not change. +.PP +This is how one would do it normally anyway, the important point is that +the libev application should not optimise around libev but should leave +optimisations to libev. +.PP +\fIThe special problem of dup'ed file descriptors\fR +.IX Subsection "The special problem of dup'ed file descriptors" +.PP +Some backends (e.g. epoll), cannot register events for file descriptors, +but only events for the underlying file descriptions. That means when you +have \f(CW\*(C`dup ()\*(C'\fR'ed file descriptors or weirder constellations, and register +events for them, only one file descriptor might actually receive events. +.PP +There is no workaround possible except not registering events +for potentially \f(CW\*(C`dup ()\*(C'\fR'ed file descriptors, or to resort to +\&\f(CW\*(C`EVBACKEND_SELECT\*(C'\fR or \f(CW\*(C`EVBACKEND_POLL\*(C'\fR. +.PP +\fIThe special problem of fork\fR +.IX Subsection "The special problem of fork" +.PP +Some backends (epoll, kqueue) do not support \f(CW\*(C`fork ()\*(C'\fR at all or exhibit +useless behaviour. Libev fully supports fork, but needs to be told about +it in the child. +.PP +To support fork in your programs, you either have to call +\&\f(CW\*(C`ev_default_fork ()\*(C'\fR or \f(CW\*(C`ev_loop_fork ()\*(C'\fR after a fork in the child, +enable \f(CW\*(C`EVFLAG_FORKCHECK\*(C'\fR, or resort to \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR or +\&\f(CW\*(C`EVBACKEND_POLL\*(C'\fR. +.PP +\fIThe special problem of \s-1SIGPIPE\s0\fR +.IX Subsection "The special problem of SIGPIPE" +.PP +While not really specific to libev, it is easy to forget about \s-1SIGPIPE:\s0 +when reading from a pipe whose other end has been closed, your program +gets send a \s-1SIGPIPE\s0, which, by default, aborts your program. For most +programs this is sensible behaviour, for daemons, this is usually +undesirable. +.PP +So when you encounter spurious, unexplained daemon exits, make sure you +ignore \s-1SIGPIPE\s0 (and maybe make sure you log the exit status of your daemon +somewhere, as that would have given you a big clue). +.PP +\fIWatcher-Specific Functions\fR +.IX Subsection "Watcher-Specific Functions" +.IP "ev_io_init (ev_io *, callback, int fd, int events)" 4 +.IX Item "ev_io_init (ev_io *, callback, int fd, int events)" +.PD 0 +.IP "ev_io_set (ev_io *, int fd, int events)" 4 +.IX Item "ev_io_set (ev_io *, int fd, int events)" +.PD +Configures an \f(CW\*(C`ev_io\*(C'\fR watcher. The \f(CW\*(C`fd\*(C'\fR is the file descriptor to +rceeive events for and events is either \f(CW\*(C`EV_READ\*(C'\fR, \f(CW\*(C`EV_WRITE\*(C'\fR or +\&\f(CW\*(C`EV_READ | EV_WRITE\*(C'\fR to receive the given events. +.IP "int fd [read\-only]" 4 +.IX Item "int fd [read-only]" +The file descriptor being watched. +.IP "int events [read\-only]" 4 +.IX Item "int events [read-only]" +The events being watched. +.PP +\fIExamples\fR +.IX Subsection "Examples" +.PP +Example: Call \f(CW\*(C`stdin_readable_cb\*(C'\fR when \s-1STDIN_FILENO\s0 has become, well +readable, but only once. Since it is likely line-buffered, you could +attempt to read a whole line in the callback. +.PP +.Vb 6 +\& static void +\& stdin_readable_cb (struct ev_loop *loop, struct ev_io *w, int revents) +\& { +\& ev_io_stop (loop, w); +\& .. read from stdin here (or from w\->fd) and haqndle any I/O errors +\& } +\& +\& ... +\& struct ev_loop *loop = ev_default_init (0); +\& struct ev_io stdin_readable; +\& ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ); +\& ev_io_start (loop, &stdin_readable); +\& ev_loop (loop, 0); +.Ve +.ie n .Sh """ev_timer"" \- relative and optionally repeating timeouts" +.el .Sh "\f(CWev_timer\fP \- relative and optionally repeating timeouts" +.IX Subsection "ev_timer - relative and optionally repeating timeouts" +Timer watchers are simple relative timers that generate an event after a +given time, and optionally repeating in regular intervals after that. +.PP +The timers are based on real time, that is, if you register an event that +times out after an hour and you reset your system clock to last years +time, it will still time out after (roughly) and hour. \*(L"Roughly\*(R" because +detecting time jumps is hard, and some inaccuracies are unavoidable (the +monotonic clock option helps a lot here). +.PP +The relative timeouts are calculated relative to the \f(CW\*(C`ev_now ()\*(C'\fR +time. This is usually the right thing as this timestamp refers to the time +of the event triggering whatever timeout you are modifying/starting. If +you suspect event processing to be delayed and you \fIneed\fR to base the timeout +on the current time, use something like this to adjust for this: +.PP +.Vb 1 +\& ev_timer_set (&timer, after + ev_now () \- ev_time (), 0.); +.Ve +.PP +The callback is guarenteed to be invoked only when its timeout has passed, +but if multiple timers become ready during the same loop iteration then +order of execution is undefined. +.PP +\fIWatcher-Specific Functions and Data Members\fR +.IX Subsection "Watcher-Specific Functions and Data Members" +.IP "ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)" 4 +.IX Item "ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)" +.PD 0 +.IP "ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)" 4 +.IX Item "ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)" +.PD +Configure the timer to trigger after \f(CW\*(C`after\*(C'\fR seconds. If \f(CW\*(C`repeat\*(C'\fR is +\&\f(CW0.\fR, then it will automatically be stopped. If it is positive, then the +timer will automatically be configured to trigger again \f(CW\*(C`repeat\*(C'\fR seconds +later, again, and again, until stopped manually. +.Sp +The timer itself will do a best-effort at avoiding drift, that is, if you +configure a timer to trigger every 10 seconds, then it will trigger at +exactly 10 second intervals. If, however, your program cannot keep up with +the timer (because it takes longer than those 10 seconds to do stuff) the +timer will not fire more than once per event loop iteration. +.IP "ev_timer_again (loop, ev_timer *)" 4 +.IX Item "ev_timer_again (loop, ev_timer *)" +This will act as if the timer timed out and restart it again if it is +repeating. The exact semantics are: +.Sp +If the timer is pending, its pending status is cleared. +.Sp +If the timer is started but nonrepeating, stop it (as if it timed out). +.Sp +If the timer is repeating, either start it if necessary (with the +\&\f(CW\*(C`repeat\*(C'\fR value), or reset the running timer to the \f(CW\*(C`repeat\*(C'\fR value. +.Sp +This sounds a bit complicated, but here is a useful and typical +example: Imagine you have a tcp connection and you want a so-called idle +timeout, that is, you want to be called when there have been, say, 60 +seconds of inactivity on the socket. The easiest way to do this is to +configure an \f(CW\*(C`ev_timer\*(C'\fR with a \f(CW\*(C`repeat\*(C'\fR value of \f(CW60\fR and then call +\&\f(CW\*(C`ev_timer_again\*(C'\fR each time you successfully read or write some data. If +you go into an idle state where you do not expect data to travel on the +socket, you can \f(CW\*(C`ev_timer_stop\*(C'\fR the timer, and \f(CW\*(C`ev_timer_again\*(C'\fR will +automatically restart it if need be. +.Sp +That means you can ignore the \f(CW\*(C`after\*(C'\fR value and \f(CW\*(C`ev_timer_start\*(C'\fR +altogether and only ever use the \f(CW\*(C`repeat\*(C'\fR value and \f(CW\*(C`ev_timer_again\*(C'\fR: +.Sp +.Vb 8 +\& ev_timer_init (timer, callback, 0., 5.); +\& ev_timer_again (loop, timer); +\& ... +\& timer\->again = 17.; +\& ev_timer_again (loop, timer); +\& ... +\& timer\->again = 10.; +\& ev_timer_again (loop, timer); +.Ve +.Sp +This is more slightly efficient then stopping/starting the timer each time +you want to modify its timeout value. +.IP "ev_tstamp repeat [read\-write]" 4 +.IX Item "ev_tstamp repeat [read-write]" +The current \f(CW\*(C`repeat\*(C'\fR value. Will be used each time the watcher times out +or \f(CW\*(C`ev_timer_again\*(C'\fR is called and determines the next timeout (if any), +which is also when any modifications are taken into account. +.PP +\fIExamples\fR +.IX Subsection "Examples" +.PP +Example: Create a timer that fires after 60 seconds. +.PP +.Vb 5 +\& static void +\& one_minute_cb (struct ev_loop *loop, struct ev_timer *w, int revents) +\& { +\& .. one minute over, w is actually stopped right here +\& } +\& +\& struct ev_timer mytimer; +\& ev_timer_init (&mytimer, one_minute_cb, 60., 0.); +\& ev_timer_start (loop, &mytimer); +.Ve +.PP +Example: Create a timeout timer that times out after 10 seconds of +inactivity. +.PP +.Vb 5 +\& static void +\& timeout_cb (struct ev_loop *loop, struct ev_timer *w, int revents) +\& { +\& .. ten seconds without any activity +\& } +\& +\& struct ev_timer mytimer; +\& ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */ +\& ev_timer_again (&mytimer); /* start timer */ +\& ev_loop (loop, 0); +\& +\& // and in some piece of code that gets executed on any "activity": +\& // reset the timeout to start ticking again at 10 seconds +\& ev_timer_again (&mytimer); +.Ve +.ie n .Sh """ev_periodic"" \- to cron or not to cron?" +.el .Sh "\f(CWev_periodic\fP \- to cron or not to cron?" +.IX Subsection "ev_periodic - to cron or not to cron?" +Periodic watchers are also timers of a kind, but they are very versatile +(and unfortunately a bit complex). +.PP +Unlike \f(CW\*(C`ev_timer\*(C'\fR's, they are not based on real time (or relative time) +but on wallclock time (absolute time). You can tell a periodic watcher +to trigger \*(L"at\*(R" some specific point in time. For example, if you tell a +periodic watcher to trigger in 10 seconds (by specifiying e.g. \f(CW\*(C`ev_now () ++ 10.\*(C'\fR) and then reset your system clock to the last year, then it will +take a year to trigger the event (unlike an \f(CW\*(C`ev_timer\*(C'\fR, which would trigger +roughly 10 seconds later). +.PP +They can also be used to implement vastly more complex timers, such as +triggering an event on each midnight, local time or other, complicated, +rules. +.PP +As with timers, the callback is guarenteed to be invoked only when the +time (\f(CW\*(C`at\*(C'\fR) has been passed, but if multiple periodic timers become ready +during the same loop iteration then order of execution is undefined. +.PP +\fIWatcher-Specific Functions and Data Members\fR +.IX Subsection "Watcher-Specific Functions and Data Members" +.IP "ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)" 4 +.IX Item "ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)" +.PD 0 +.IP "ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)" 4 +.IX Item "ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)" +.PD +Lots of arguments, lets sort it out... There are basically three modes of +operation, and we will explain them from simplest to complex: +.RS 4 +.IP "\(bu" 4 +absolute timer (at = time, interval = reschedule_cb = 0) +.Sp +In this configuration the watcher triggers an event at the wallclock time +\&\f(CW\*(C`at\*(C'\fR and doesn't repeat. It will not adjust when a time jump occurs, +that is, if it is to be run at January 1st 2011 then it will run when the +system time reaches or surpasses this time. +.IP "\(bu" 4 +repeating interval timer (at = offset, interval > 0, reschedule_cb = 0) +.Sp +In this mode the watcher will always be scheduled to time out at the next +\&\f(CW\*(C`at + N * interval\*(C'\fR time (for some integer N, which can also be negative) +and then repeat, regardless of any time jumps. +.Sp +This can be used to create timers that do not drift with respect to system +time: +.Sp +.Vb 1 +\& ev_periodic_set (&periodic, 0., 3600., 0); +.Ve +.Sp +This doesn't mean there will always be 3600 seconds in between triggers, +but only that the the callback will be called when the system time shows a +full hour (\s-1UTC\s0), or more correctly, when the system time is evenly divisible +by 3600. +.Sp +Another way to think about it (for the mathematically inclined) is that +\&\f(CW\*(C`ev_periodic\*(C'\fR will try to run the callback in this mode at the next possible +time where \f(CW\*(C`time = at (mod interval)\*(C'\fR, regardless of any time jumps. +.Sp +For numerical stability it is preferable that the \f(CW\*(C`at\*(C'\fR value is near +\&\f(CW\*(C`ev_now ()\*(C'\fR (the current time), but there is no range requirement for +this value. +.IP "\(bu" 4 +manual reschedule mode (at and interval ignored, reschedule_cb = callback) +.Sp +In this mode the values for \f(CW\*(C`interval\*(C'\fR and \f(CW\*(C`at\*(C'\fR are both being +ignored. Instead, each time the periodic watcher gets scheduled, the +reschedule callback will be called with the watcher as first, and the +current time as second argument. +.Sp +\&\s-1NOTE:\s0 \fIThis callback \s-1MUST\s0 \s-1NOT\s0 stop or destroy any periodic watcher, +ever, or make any event loop modifications\fR. If you need to stop it, +return \f(CW\*(C`now + 1e30\*(C'\fR (or so, fudge fudge) and stop it afterwards (e.g. by +starting an \f(CW\*(C`ev_prepare\*(C'\fR watcher, which is legal). +.Sp +Its prototype is \f(CW\*(C`ev_tstamp (*reschedule_cb)(struct ev_periodic *w, +ev_tstamp now)\*(C'\fR, e.g.: +.Sp +.Vb 4 +\& static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now) +\& { +\& return now + 60.; +\& } +.Ve +.Sp +It must return the next time to trigger, based on the passed time value +(that is, the lowest time value larger than to the second argument). It +will usually be called just before the callback will be triggered, but +might be called at other times, too. +.Sp +\&\s-1NOTE:\s0 \fIThis callback must always return a time that is later than the +passed \f(CI\*(C`now\*(C'\fI value\fR. Not even \f(CW\*(C`now\*(C'\fR itself will do, it \fImust\fR be larger. +.Sp +This can be used to create very complex timers, such as a timer that +triggers on each midnight, local time. To do this, you would calculate the +next midnight after \f(CW\*(C`now\*(C'\fR and return the timestamp value for this. How +you do this is, again, up to you (but it is not trivial, which is the main +reason I omitted it as an example). +.RE +.RS 4 +.RE +.IP "ev_periodic_again (loop, ev_periodic *)" 4 +.IX Item "ev_periodic_again (loop, ev_periodic *)" +Simply stops and restarts the periodic watcher again. This is only useful +when you changed some parameters or the reschedule callback would return +a different time than the last time it was called (e.g. in a crond like +program when the crontabs have changed). +.IP "ev_tstamp ev_periodic_at (ev_periodic *)" 4 +.IX Item "ev_tstamp ev_periodic_at (ev_periodic *)" +When active, returns the absolute time that the watcher is supposed to +trigger next. +.IP "ev_tstamp offset [read\-write]" 4 +.IX Item "ev_tstamp offset [read-write]" +When repeating, this contains the offset value, otherwise this is the +absolute point in time (the \f(CW\*(C`at\*(C'\fR value passed to \f(CW\*(C`ev_periodic_set\*(C'\fR). +.Sp +Can be modified any time, but changes only take effect when the periodic +timer fires or \f(CW\*(C`ev_periodic_again\*(C'\fR is being called. +.IP "ev_tstamp interval [read\-write]" 4 +.IX Item "ev_tstamp interval [read-write]" +The current interval value. Can be modified any time, but changes only +take effect when the periodic timer fires or \f(CW\*(C`ev_periodic_again\*(C'\fR is being +called. +.IP "ev_tstamp (*reschedule_cb)(struct ev_periodic *w, ev_tstamp now) [read\-write]" 4 +.IX Item "ev_tstamp (*reschedule_cb)(struct ev_periodic *w, ev_tstamp now) [read-write]" +The current reschedule callback, or \f(CW0\fR, if this functionality is +switched off. Can be changed any time, but changes only take effect when +the periodic timer fires or \f(CW\*(C`ev_periodic_again\*(C'\fR is being called. +.PP +\fIExamples\fR +.IX Subsection "Examples" +.PP +Example: Call a callback every hour, or, more precisely, whenever the +system clock is divisible by 3600. The callback invocation times have +potentially a lot of jittering, but good long-term stability. +.PP +.Vb 5 +\& static void +\& clock_cb (struct ev_loop *loop, struct ev_io *w, int revents) +\& { +\& ... its now a full hour (UTC, or TAI or whatever your clock follows) +\& } +\& +\& struct ev_periodic hourly_tick; +\& ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0); +\& ev_periodic_start (loop, &hourly_tick); +.Ve +.PP +Example: The same as above, but use a reschedule callback to do it: +.PP +.Vb 1 +\& #include <math.h> +\& +\& static ev_tstamp +\& my_scheduler_cb (struct ev_periodic *w, ev_tstamp now) +\& { +\& return fmod (now, 3600.) + 3600.; +\& } +\& +\& ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb); +.Ve +.PP +Example: Call a callback every hour, starting now: +.PP +.Vb 4 +\& struct ev_periodic hourly_tick; +\& ev_periodic_init (&hourly_tick, clock_cb, +\& fmod (ev_now (loop), 3600.), 3600., 0); +\& ev_periodic_start (loop, &hourly_tick); +.Ve +.ie n .Sh """ev_signal"" \- signal me when a signal gets signalled!" +.el .Sh "\f(CWev_signal\fP \- signal me when a signal gets signalled!" +.IX Subsection "ev_signal - signal me when a signal gets signalled!" +Signal watchers will trigger an event when the process receives a specific +signal one or more times. Even though signals are very asynchronous, libev +will try it's best to deliver signals synchronously, i.e. as part of the +normal event processing, like any other event. +.PP +You can configure as many watchers as you like per signal. Only when the +first watcher gets started will libev actually register a signal watcher +with the kernel (thus it coexists with your own signal handlers as long +as you don't register any with libev). Similarly, when the last signal +watcher for a signal is stopped libev will reset the signal handler to +\&\s-1SIG_DFL\s0 (regardless of what it was set to before). +.PP +If possible and supported, libev will install its handlers with +\&\f(CW\*(C`SA_RESTART\*(C'\fR behaviour enabled, so syscalls should not be unduly +interrupted. If you have a problem with syscalls getting interrupted by +signals you can block all signals in an \f(CW\*(C`ev_check\*(C'\fR watcher and unblock +them in an \f(CW\*(C`ev_prepare\*(C'\fR watcher. +.PP +\fIWatcher-Specific Functions and Data Members\fR +.IX Subsection "Watcher-Specific Functions and Data Members" +.IP "ev_signal_init (ev_signal *, callback, int signum)" 4 +.IX Item "ev_signal_init (ev_signal *, callback, int signum)" +.PD 0 +.IP "ev_signal_set (ev_signal *, int signum)" 4 +.IX Item "ev_signal_set (ev_signal *, int signum)" +.PD +Configures the watcher to trigger on the given signal number (usually one +of the \f(CW\*(C`SIGxxx\*(C'\fR constants). +.IP "int signum [read\-only]" 4 +.IX Item "int signum [read-only]" +The signal the watcher watches out for. +.PP +\fIExamples\fR +.IX Subsection "Examples" +.PP +Example: Try to exit cleanly on \s-1SIGINT\s0 and \s-1SIGTERM\s0. +.PP +.Vb 5 +\& static void +\& sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents) +\& { +\& ev_unloop (loop, EVUNLOOP_ALL); +\& } +\& +\& struct ev_signal signal_watcher; +\& ev_signal_init (&signal_watcher, sigint_cb, SIGINT); +\& ev_signal_start (loop, &sigint_cb); +.Ve +.ie n .Sh """ev_child"" \- watch out for process status changes" +.el .Sh "\f(CWev_child\fP \- watch out for process status changes" +.IX Subsection "ev_child - watch out for process status changes" +Child watchers trigger when your process receives a \s-1SIGCHLD\s0 in response to +some child status changes (most typically when a child of yours dies). It +is permissible to install a child watcher \fIafter\fR the child has been +forked (which implies it might have already exited), as long as the event +loop isn't entered (or is continued from a watcher). +.PP +Only the default event loop is capable of handling signals, and therefore +you can only rgeister child watchers in the default event loop. +.PP +\fIProcess Interaction\fR +.IX Subsection "Process Interaction" +.PP +Libev grabs \f(CW\*(C`SIGCHLD\*(C'\fR as soon as the default event loop is +initialised. This is necessary to guarantee proper behaviour even if +the first child watcher is started after the child exits. The occurance +of \f(CW\*(C`SIGCHLD\*(C'\fR is recorded asynchronously, but child reaping is done +synchronously as part of the event loop processing. Libev always reaps all +children, even ones not watched. +.PP +\fIOverriding the Built-In Processing\fR +.IX Subsection "Overriding the Built-In Processing" +.PP +Libev offers no special support for overriding the built-in child +processing, but if your application collides with libev's default child +handler, you can override it easily by installing your own handler for +\&\f(CW\*(C`SIGCHLD\*(C'\fR after initialising the default loop, and making sure the +default loop never gets destroyed. You are encouraged, however, to use an +event-based approach to child reaping and thus use libev's support for +that, so other libev users can use \f(CW\*(C`ev_child\*(C'\fR watchers freely. +.PP +\fIWatcher-Specific Functions and Data Members\fR +.IX Subsection "Watcher-Specific Functions and Data Members" +.IP "ev_child_init (ev_child *, callback, int pid, int trace)" 4 +.IX Item "ev_child_init (ev_child *, callback, int pid, int trace)" +.PD 0 +.IP "ev_child_set (ev_child *, int pid, int trace)" 4 +.IX Item "ev_child_set (ev_child *, int pid, int trace)" +.PD +Configures the watcher to wait for status changes of process \f(CW\*(C`pid\*(C'\fR (or +\&\fIany\fR process if \f(CW\*(C`pid\*(C'\fR is specified as \f(CW0\fR). The callback can look +at the \f(CW\*(C`rstatus\*(C'\fR member of the \f(CW\*(C`ev_child\*(C'\fR watcher structure to see +the status word (use the macros from \f(CW\*(C`sys/wait.h\*(C'\fR and see your systems +\&\f(CW\*(C`waitpid\*(C'\fR documentation). The \f(CW\*(C`rpid\*(C'\fR member contains the pid of the +process causing the status change. \f(CW\*(C`trace\*(C'\fR must be either \f(CW0\fR (only +activate the watcher when the process terminates) or \f(CW1\fR (additionally +activate the watcher when the process is stopped or continued). +.IP "int pid [read\-only]" 4 +.IX Item "int pid [read-only]" +The process id this watcher watches out for, or \f(CW0\fR, meaning any process id. +.IP "int rpid [read\-write]" 4 +.IX Item "int rpid [read-write]" +The process id that detected a status change. +.IP "int rstatus [read\-write]" 4 +.IX Item "int rstatus [read-write]" +The process exit/trace status caused by \f(CW\*(C`rpid\*(C'\fR (see your systems +\&\f(CW\*(C`waitpid\*(C'\fR and \f(CW\*(C`sys/wait.h\*(C'\fR documentation for details). +.PP +\fIExamples\fR +.IX Subsection "Examples" +.PP +Example: \f(CW\*(C`fork()\*(C'\fR a new process and install a child handler to wait for +its completion. +.PP +.Vb 1 +\& ev_child cw; +\& +\& static void +\& child_cb (EV_P_ struct ev_child *w, int revents) +\& { +\& ev_child_stop (EV_A_ w); +\& printf ("process %d exited with status %x\en", w\->rpid, w\->rstatus); +\& } +\& +\& pid_t pid = fork (); +\& +\& if (pid < 0) +\& // error +\& else if (pid == 0) +\& { +\& // the forked child executes here +\& exit (1); +\& } +\& else +\& { +\& ev_child_init (&cw, child_cb, pid, 0); +\& ev_child_start (EV_DEFAULT_ &cw); +\& } +.Ve +.ie n .Sh """ev_stat"" \- did the file attributes just change?" +.el .Sh "\f(CWev_stat\fP \- did the file attributes just change?" +.IX Subsection "ev_stat - did the file attributes just change?" +This watches a filesystem path for attribute changes. That is, it calls +\&\f(CW\*(C`stat\*(C'\fR regularly (or when the \s-1OS\s0 says it changed) and sees if it changed +compared to the last time, invoking the callback if it did. +.PP +The path does not need to exist: changing from \*(L"path exists\*(R" to \*(L"path does +not exist\*(R" is a status change like any other. The condition \*(L"path does +not exist\*(R" is signified by the \f(CW\*(C`st_nlink\*(C'\fR field being zero (which is +otherwise always forced to be at least one) and all the other fields of +the stat buffer having unspecified contents. +.PP +The path \fIshould\fR be absolute and \fImust not\fR end in a slash. If it is +relative and your working directory changes, the behaviour is undefined. +.PP +Since there is no standard to do this, the portable implementation simply +calls \f(CW\*(C`stat (2)\*(C'\fR regularly on the path to see if it changed somehow. You +can specify a recommended polling interval for this case. If you specify +a polling interval of \f(CW0\fR (highly recommended!) then a \fIsuitable, +unspecified default\fR value will be used (which you can expect to be around +five seconds, although this might change dynamically). Libev will also +impose a minimum interval which is currently around \f(CW0.1\fR, but thats +usually overkill. +.PP +This watcher type is not meant for massive numbers of stat watchers, +as even with OS-supported change notifications, this can be +resource-intensive. +.PP +At the time of this writing, only the Linux inotify interface is +implemented (implementing kqueue support is left as an exercise for the +reader, note, however, that the author sees no way of implementing ev_stat +semantics with kqueue). Inotify will be used to give hints only and should +not change the semantics of \f(CW\*(C`ev_stat\*(C'\fR watchers, which means that libev +sometimes needs to fall back to regular polling again even with inotify, +but changes are usually detected immediately, and if the file exists there +will be no polling. +.PP +\fI\s-1ABI\s0 Issues (Largefile Support)\fR +.IX Subsection "ABI Issues (Largefile Support)" +.PP +Libev by default (unless the user overrides this) uses the default +compilation environment, which means that on systems with optionally +disabled large file support, you get the 32 bit version of the stat +structure. When using the library from programs that change the \s-1ABI\s0 to +use 64 bit file offsets the programs will fail. In that case you have to +compile libev with the same flags to get binary compatibility. This is +obviously the case with any flags that change the \s-1ABI\s0, but the problem is +most noticably with ev_stat and largefile support. +.PP +\fIInotify\fR +.IX Subsection "Inotify" +.PP +When \f(CW\*(C`inotify (7)\*(C'\fR support has been compiled into libev (generally only +available on Linux) and present at runtime, it will be used to speed up +change detection where possible. The inotify descriptor will be created lazily +when the first \f(CW\*(C`ev_stat\*(C'\fR watcher is being started. +.PP +Inotify presence does not change the semantics of \f(CW\*(C`ev_stat\*(C'\fR watchers +except that changes might be detected earlier, and in some cases, to avoid +making regular \f(CW\*(C`stat\*(C'\fR calls. Even in the presence of inotify support +there are many cases where libev has to resort to regular \f(CW\*(C`stat\*(C'\fR polling. +.PP +(There is no support for kqueue, as apparently it cannot be used to +implement this functionality, due to the requirement of having a file +descriptor open on the object at all times). +.PP +\fIThe special problem of stat time resolution\fR +.IX Subsection "The special problem of stat time resolution" +.PP +The \f(CW\*(C`stat ()\*(C'\fR syscall only supports full-second resolution portably, and +even on systems where the resolution is higher, many filesystems still +only support whole seconds. +.PP +That means that, if the time is the only thing that changes, you can +easily miss updates: on the first update, \f(CW\*(C`ev_stat\*(C'\fR detects a change and +calls your callback, which does something. When there is another update +within the same second, \f(CW\*(C`ev_stat\*(C'\fR will be unable to detect it as the stat +data does not change. +.PP +The solution to this is to delay acting on a change for slightly more +than second (or till slightly after the next full second boundary), using +a roughly one-second-delay \f(CW\*(C`ev_timer\*(C'\fR (e.g. \f(CW\*(C`ev_timer_set (w, 0., 1.02); +ev_timer_again (loop, w)\*(C'\fR). +.PP +The \f(CW.02\fR offset is added to work around small timing inconsistencies +of some operating systems (where the second counter of the current time +might be be delayed. One such system is the Linux kernel, where a call to +\&\f(CW\*(C`gettimeofday\*(C'\fR might return a timestamp with a full second later than +a subsequent \f(CW\*(C`time\*(C'\fR call \- if the equivalent of \f(CW\*(C`time ()\*(C'\fR is used to +update file times then there will be a small window where the kernel uses +the previous second to update file times but libev might already execute +the timer callback). +.PP +\fIWatcher-Specific Functions and Data Members\fR +.IX Subsection "Watcher-Specific Functions and Data Members" +.IP "ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)" 4 +.IX Item "ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)" +.PD 0 +.IP "ev_stat_set (ev_stat *, const char *path, ev_tstamp interval)" 4 +.IX Item "ev_stat_set (ev_stat *, const char *path, ev_tstamp interval)" +.PD +Configures the watcher to wait for status changes of the given +\&\f(CW\*(C`path\*(C'\fR. The \f(CW\*(C`interval\*(C'\fR is a hint on how quickly a change is expected to +be detected and should normally be specified as \f(CW0\fR to let libev choose +a suitable value. The memory pointed to by \f(CW\*(C`path\*(C'\fR must point to the same +path for as long as the watcher is active. +.Sp +The callback will receive \f(CW\*(C`EV_STAT\*(C'\fR when a change was detected, relative +to the attributes at the time the watcher was started (or the last change +was detected). +.IP "ev_stat_stat (loop, ev_stat *)" 4 +.IX Item "ev_stat_stat (loop, ev_stat *)" +Updates the stat buffer immediately with new values. If you change the +watched path in your callback, you could call this function to avoid +detecting this change (while introducing a race condition if you are not +the only one changing the path). Can also be useful simply to find out the +new values. +.IP "ev_statdata attr [read\-only]" 4 +.IX Item "ev_statdata attr [read-only]" +The most-recently detected attributes of the file. Although the type is +\&\f(CW\*(C`ev_statdata\*(C'\fR, this is usually the (or one of the) \f(CW\*(C`struct stat\*(C'\fR types +suitable for your system, but you can only rely on the POSIX-standardised +members to be present. If the \f(CW\*(C`st_nlink\*(C'\fR member is \f(CW0\fR, then there was +some error while \f(CW\*(C`stat\*(C'\fRing the file. +.IP "ev_statdata prev [read\-only]" 4 +.IX Item "ev_statdata prev [read-only]" +The previous attributes of the file. The callback gets invoked whenever +\&\f(CW\*(C`prev\*(C'\fR != \f(CW\*(C`attr\*(C'\fR, or, more precisely, one or more of these members +differ: \f(CW\*(C`st_dev\*(C'\fR, \f(CW\*(C`st_ino\*(C'\fR, \f(CW\*(C`st_mode\*(C'\fR, \f(CW\*(C`st_nlink\*(C'\fR, \f(CW\*(C`st_uid\*(C'\fR, +\&\f(CW\*(C`st_gid\*(C'\fR, \f(CW\*(C`st_rdev\*(C'\fR, \f(CW\*(C`st_size\*(C'\fR, \f(CW\*(C`st_atime\*(C'\fR, \f(CW\*(C`st_mtime\*(C'\fR, \f(CW\*(C`st_ctime\*(C'\fR. +.IP "ev_tstamp interval [read\-only]" 4 +.IX Item "ev_tstamp interval [read-only]" +The specified interval. +.IP "const char *path [read\-only]" 4 +.IX Item "const char *path [read-only]" +The filesystem path that is being watched. +.PP +\fIExamples\fR +.IX Subsection "Examples" +.PP +Example: Watch \f(CW\*(C`/etc/passwd\*(C'\fR for attribute changes. +.PP +.Vb 10 +\& static void +\& passwd_cb (struct ev_loop *loop, ev_stat *w, int revents) +\& { +\& /* /etc/passwd changed in some way */ +\& if (w\->attr.st_nlink) +\& { +\& printf ("passwd current size %ld\en", (long)w\->attr.st_size); +\& printf ("passwd current atime %ld\en", (long)w\->attr.st_mtime); +\& printf ("passwd current mtime %ld\en", (long)w\->attr.st_mtime); +\& } +\& else +\& /* you shalt not abuse printf for puts */ +\& puts ("wow, /etc/passwd is not there, expect problems. " +\& "if this is windows, they already arrived\en"); +\& } +\& +\& ... +\& ev_stat passwd; +\& +\& ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.); +\& ev_stat_start (loop, &passwd); +.Ve +.PP +Example: Like above, but additionally use a one-second delay so we do not +miss updates (however, frequent updates will delay processing, too, so +one might do the work both on \f(CW\*(C`ev_stat\*(C'\fR callback invocation \fIand\fR on +\&\f(CW\*(C`ev_timer\*(C'\fR callback invocation). +.PP +.Vb 2 +\& static ev_stat passwd; +\& static ev_timer timer; +\& +\& static void +\& timer_cb (EV_P_ ev_timer *w, int revents) +\& { +\& ev_timer_stop (EV_A_ w); +\& +\& /* now it\*(Aqs one second after the most recent passwd change */ +\& } +\& +\& static void +\& stat_cb (EV_P_ ev_stat *w, int revents) +\& { +\& /* reset the one\-second timer */ +\& ev_timer_again (EV_A_ &timer); +\& } +\& +\& ... +\& ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.); +\& ev_stat_start (loop, &passwd); +\& ev_timer_init (&timer, timer_cb, 0., 1.02); +.Ve +.ie n .Sh """ev_idle"" \- when you've got nothing better to do..." +.el .Sh "\f(CWev_idle\fP \- when you've got nothing better to do..." +.IX Subsection "ev_idle - when you've got nothing better to do..." +Idle watchers trigger events when no other events of the same or higher +priority are pending (prepare, check and other idle watchers do not +count). +.PP +That is, as long as your process is busy handling sockets or timeouts +(or even signals, imagine) of the same or higher priority it will not be +triggered. But when your process is idle (or only lower-priority watchers +are pending), the idle watchers are being called once per event loop +iteration \- until stopped, that is, or your process receives more events +and becomes busy again with higher priority stuff. +.PP +The most noteworthy effect is that as long as any idle watchers are +active, the process will not block when waiting for new events. +.PP +Apart from keeping your process non-blocking (which is a useful +effect on its own sometimes), idle watchers are a good place to do +\&\*(L"pseudo-background processing\*(R", or delay processing stuff to after the +event loop has handled all outstanding events. +.PP +\fIWatcher-Specific Functions and Data Members\fR +.IX Subsection "Watcher-Specific Functions and Data Members" +.IP "ev_idle_init (ev_signal *, callback)" 4 +.IX Item "ev_idle_init (ev_signal *, callback)" +Initialises and configures the idle watcher \- it has no parameters of any +kind. There is a \f(CW\*(C`ev_idle_set\*(C'\fR macro, but using it is utterly pointless, +believe me. +.PP +\fIExamples\fR +.IX Subsection "Examples" +.PP +Example: Dynamically allocate an \f(CW\*(C`ev_idle\*(C'\fR watcher, start it, and in the +callback, free it. Also, use no error checking, as usual. +.PP +.Vb 7 +\& static void +\& idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents) +\& { +\& free (w); +\& // now do something you wanted to do when the program has +\& // no longer anything immediate to do. +\& } +\& +\& struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle)); +\& ev_idle_init (idle_watcher, idle_cb); +\& ev_idle_start (loop, idle_cb); +.Ve +.ie n .Sh """ev_prepare""\fP and \f(CW""ev_check"" \- customise your event loop!" +.el .Sh "\f(CWev_prepare\fP and \f(CWev_check\fP \- customise your event loop!" +.IX Subsection "ev_prepare and ev_check - customise your event loop!" +Prepare and check watchers are usually (but not always) used in tandem: +prepare watchers get invoked before the process blocks and check watchers +afterwards. +.PP +You \fImust not\fR call \f(CW\*(C`ev_loop\*(C'\fR or similar functions that enter +the current event loop from either \f(CW\*(C`ev_prepare\*(C'\fR or \f(CW\*(C`ev_check\*(C'\fR +watchers. Other loops than the current one are fine, however. The +rationale behind this is that you do not need to check for recursion in +those watchers, i.e. the sequence will always be \f(CW\*(C`ev_prepare\*(C'\fR, blocking, +\&\f(CW\*(C`ev_check\*(C'\fR so if you have one watcher of each kind they will always be +called in pairs bracketing the blocking call. +.PP +Their main purpose is to integrate other event mechanisms into libev and +their use is somewhat advanced. This could be used, for example, to track +variable changes, implement your own watchers, integrate net-snmp or a +coroutine library and lots more. They are also occasionally useful if +you cache some data and want to flush it before blocking (for example, +in X programs you might want to do an \f(CW\*(C`XFlush ()\*(C'\fR in an \f(CW\*(C`ev_prepare\*(C'\fR +watcher). +.PP +This is done by examining in each prepare call which file descriptors need +to be watched by the other library, registering \f(CW\*(C`ev_io\*(C'\fR watchers for +them and starting an \f(CW\*(C`ev_timer\*(C'\fR watcher for any timeouts (many libraries +provide just this functionality). Then, in the check watcher you check for +any events that occured (by checking the pending status of all watchers +and stopping them) and call back into the library. The I/O and timer +callbacks will never actually be called (but must be valid nevertheless, +because you never know, you know?). +.PP +As another example, the Perl Coro module uses these hooks to integrate +coroutines into libev programs, by yielding to other active coroutines +during each prepare and only letting the process block if no coroutines +are ready to run (it's actually more complicated: it only runs coroutines +with priority higher than or equal to the event loop and one coroutine +of lower priority, but only once, using idle watchers to keep the event +loop from blocking if lower-priority coroutines are active, thus mapping +low-priority coroutines to idle/background tasks). +.PP +It is recommended to give \f(CW\*(C`ev_check\*(C'\fR watchers highest (\f(CW\*(C`EV_MAXPRI\*(C'\fR) +priority, to ensure that they are being run before any other watchers +after the poll. Also, \f(CW\*(C`ev_check\*(C'\fR watchers (and \f(CW\*(C`ev_prepare\*(C'\fR watchers, +too) should not activate (\*(L"feed\*(R") events into libev. While libev fully +supports this, they might get executed before other \f(CW\*(C`ev_check\*(C'\fR watchers +did their job. As \f(CW\*(C`ev_check\*(C'\fR watchers are often used to embed other +(non-libev) event loops those other event loops might be in an unusable +state until their \f(CW\*(C`ev_check\*(C'\fR watcher ran (always remind yourself to +coexist peacefully with others). +.PP +\fIWatcher-Specific Functions and Data Members\fR +.IX Subsection "Watcher-Specific Functions and Data Members" +.IP "ev_prepare_init (ev_prepare *, callback)" 4 +.IX Item "ev_prepare_init (ev_prepare *, callback)" +.PD 0 +.IP "ev_check_init (ev_check *, callback)" 4 +.IX Item "ev_check_init (ev_check *, callback)" +.PD +Initialises and configures the prepare or check watcher \- they have no +parameters of any kind. There are \f(CW\*(C`ev_prepare_set\*(C'\fR and \f(CW\*(C`ev_check_set\*(C'\fR +macros, but using them is utterly, utterly and completely pointless. +.PP +\fIExamples\fR +.IX Subsection "Examples" +.PP +There are a number of principal ways to embed other event loops or modules +into libev. Here are some ideas on how to include libadns into libev +(there is a Perl module named \f(CW\*(C`EV::ADNS\*(C'\fR that does this, which you could +use as a working example. Another Perl module named \f(CW\*(C`EV::Glib\*(C'\fR embeds a +Glib main context into libev, and finally, \f(CW\*(C`Glib::EV\*(C'\fR embeds \s-1EV\s0 into the +Glib event loop). +.PP +Method 1: Add \s-1IO\s0 watchers and a timeout watcher in a prepare handler, +and in a check watcher, destroy them and call into libadns. What follows +is pseudo-code only of course. This requires you to either use a low +priority for the check watcher or use \f(CW\*(C`ev_clear_pending\*(C'\fR explicitly, as +the callbacks for the IO/timeout watchers might not have been called yet. +.PP +.Vb 2 +\& static ev_io iow [nfd]; +\& static ev_timer tw; +\& +\& static void +\& io_cb (ev_loop *loop, ev_io *w, int revents) +\& { +\& } +\& +\& // create io watchers for each fd and a timer before blocking +\& static void +\& adns_prepare_cb (ev_loop *loop, ev_prepare *w, int revents) +\& { +\& int timeout = 3600000; +\& struct pollfd fds [nfd]; +\& // actual code will need to loop here and realloc etc. +\& adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ())); +\& +\& /* the callback is illegal, but won\*(Aqt be called as we stop during check */ +\& ev_timer_init (&tw, 0, timeout * 1e\-3); +\& ev_timer_start (loop, &tw); +\& +\& // create one ev_io per pollfd +\& for (int i = 0; i < nfd; ++i) +\& { +\& ev_io_init (iow + i, io_cb, fds [i].fd, +\& ((fds [i].events & POLLIN ? EV_READ : 0) +\& | (fds [i].events & POLLOUT ? EV_WRITE : 0))); +\& +\& fds [i].revents = 0; +\& ev_io_start (loop, iow + i); +\& } +\& } +\& +\& // stop all watchers after blocking +\& static void +\& adns_check_cb (ev_loop *loop, ev_check *w, int revents) +\& { +\& ev_timer_stop (loop, &tw); +\& +\& for (int i = 0; i < nfd; ++i) +\& { +\& // set the relevant poll flags +\& // could also call adns_processreadable etc. here +\& struct pollfd *fd = fds + i; +\& int revents = ev_clear_pending (iow + i); +\& if (revents & EV_READ ) fd\->revents |= fd\->events & POLLIN; +\& if (revents & EV_WRITE) fd\->revents |= fd\->events & POLLOUT; +\& +\& // now stop the watcher +\& ev_io_stop (loop, iow + i); +\& } +\& +\& adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop)); +\& } +.Ve +.PP +Method 2: This would be just like method 1, but you run \f(CW\*(C`adns_afterpoll\*(C'\fR +in the prepare watcher and would dispose of the check watcher. +.PP +Method 3: If the module to be embedded supports explicit event +notification (adns does), you can also make use of the actual watcher +callbacks, and only destroy/create the watchers in the prepare watcher. +.PP +.Vb 5 +\& static void +\& timer_cb (EV_P_ ev_timer *w, int revents) +\& { +\& adns_state ads = (adns_state)w\->data; +\& update_now (EV_A); +\& +\& adns_processtimeouts (ads, &tv_now); +\& } +\& +\& static void +\& io_cb (EV_P_ ev_io *w, int revents) +\& { +\& adns_state ads = (adns_state)w\->data; +\& update_now (EV_A); +\& +\& if (revents & EV_READ ) adns_processreadable (ads, w\->fd, &tv_now); +\& if (revents & EV_WRITE) adns_processwriteable (ads, w\->fd, &tv_now); +\& } +\& +\& // do not ever call adns_afterpoll +.Ve +.PP +Method 4: Do not use a prepare or check watcher because the module you +want to embed is too inflexible to support it. Instead, youc na override +their poll function. The drawback with this solution is that the main +loop is now no longer controllable by \s-1EV\s0. The \f(CW\*(C`Glib::EV\*(C'\fR module does +this. +.PP +.Vb 4 +\& static gint +\& event_poll_func (GPollFD *fds, guint nfds, gint timeout) +\& { +\& int got_events = 0; +\& +\& for (n = 0; n < nfds; ++n) +\& // create/start io watcher that sets the relevant bits in fds[n] and increment got_events +\& +\& if (timeout >= 0) +\& // create/start timer +\& +\& // poll +\& ev_loop (EV_A_ 0); +\& +\& // stop timer again +\& if (timeout >= 0) +\& ev_timer_stop (EV_A_ &to); +\& +\& // stop io watchers again \- their callbacks should have set +\& for (n = 0; n < nfds; ++n) +\& ev_io_stop (EV_A_ iow [n]); +\& +\& return got_events; +\& } +.Ve +.ie n .Sh """ev_embed"" \- when one backend isn't enough..." +.el .Sh "\f(CWev_embed\fP \- when one backend isn't enough..." +.IX Subsection "ev_embed - when one backend isn't enough..." +This is a rather advanced watcher type that lets you embed one event loop +into another (currently only \f(CW\*(C`ev_io\*(C'\fR events are supported in the embedded +loop, other types of watchers might be handled in a delayed or incorrect +fashion and must not be used). +.PP +There are primarily two reasons you would want that: work around bugs and +prioritise I/O. +.PP +As an example for a bug workaround, the kqueue backend might only support +sockets on some platform, so it is unusable as generic backend, but you +still want to make use of it because you have many sockets and it scales +so nicely. In this case, you would create a kqueue-based loop and embed it +into your default loop (which might use e.g. poll). Overall operation will +be a bit slower because first libev has to poll and then call kevent, but +at least you can use both at what they are best. +.PP +As for prioritising I/O: rarely you have the case where some fds have +to be watched and handled very quickly (with low latency), and even +priorities and idle watchers might have too much overhead. In this case +you would put all the high priority stuff in one loop and all the rest in +a second one, and embed the second one in the first. +.PP +As long as the watcher is active, the callback will be invoked every time +there might be events pending in the embedded loop. The callback must then +call \f(CW\*(C`ev_embed_sweep (mainloop, watcher)\*(C'\fR to make a single sweep and invoke +their callbacks (you could also start an idle watcher to give the embedded +loop strictly lower priority for example). You can also set the callback +to \f(CW0\fR, in which case the embed watcher will automatically execute the +embedded loop sweep. +.PP +As long as the watcher is started it will automatically handle events. The +callback will be invoked whenever some events have been handled. You can +set the callback to \f(CW0\fR to avoid having to specify one if you are not +interested in that. +.PP +Also, there have not currently been made special provisions for forking: +when you fork, you not only have to call \f(CW\*(C`ev_loop_fork\*(C'\fR on both loops, +but you will also have to stop and restart any \f(CW\*(C`ev_embed\*(C'\fR watchers +yourself. +.PP +Unfortunately, not all backends are embeddable, only the ones returned by +\&\f(CW\*(C`ev_embeddable_backends\*(C'\fR are, which, unfortunately, does not include any +portable one. +.PP +So when you want to use this feature you will always have to be prepared +that you cannot get an embeddable loop. The recommended way to get around +this is to have a separate variables for your embeddable loop, try to +create it, and if that fails, use the normal loop for everything. +.PP +\fIWatcher-Specific Functions and Data Members\fR +.IX Subsection "Watcher-Specific Functions and Data Members" +.IP "ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)" 4 +.IX Item "ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)" +.PD 0 +.IP "ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)" 4 +.IX Item "ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)" +.PD +Configures the watcher to embed the given loop, which must be +embeddable. If the callback is \f(CW0\fR, then \f(CW\*(C`ev_embed_sweep\*(C'\fR will be +invoked automatically, otherwise it is the responsibility of the callback +to invoke it (it will continue to be called until the sweep has been done, +if you do not want thta, you need to temporarily stop the embed watcher). +.IP "ev_embed_sweep (loop, ev_embed *)" 4 +.IX Item "ev_embed_sweep (loop, ev_embed *)" +Make a single, non-blocking sweep over the embedded loop. This works +similarly to \f(CW\*(C`ev_loop (embedded_loop, EVLOOP_NONBLOCK)\*(C'\fR, but in the most +apropriate way for embedded loops. +.IP "struct ev_loop *other [read\-only]" 4 +.IX Item "struct ev_loop *other [read-only]" +The embedded event loop. +.PP +\fIExamples\fR +.IX Subsection "Examples" +.PP +Example: Try to get an embeddable event loop and embed it into the default +event loop. If that is not possible, use the default loop. The default +loop is stored in \f(CW\*(C`loop_hi\*(C'\fR, while the mebeddable loop is stored in +\&\f(CW\*(C`loop_lo\*(C'\fR (which is \f(CW\*(C`loop_hi\*(C'\fR in the acse no embeddable loop can be +used). +.PP +.Vb 3 +\& struct ev_loop *loop_hi = ev_default_init (0); +\& struct ev_loop *loop_lo = 0; +\& struct ev_embed embed; +\& +\& // see if there is a chance of getting one that works +\& // (remember that a flags value of 0 means autodetection) +\& loop_lo = ev_embeddable_backends () & ev_recommended_backends () +\& ? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ()) +\& : 0; +\& +\& // if we got one, then embed it, otherwise default to loop_hi +\& if (loop_lo) +\& { +\& ev_embed_init (&embed, 0, loop_lo); +\& ev_embed_start (loop_hi, &embed); +\& } +\& else +\& loop_lo = loop_hi; +.Ve +.PP +Example: Check if kqueue is available but not recommended and create +a kqueue backend for use with sockets (which usually work with any +kqueue implementation). Store the kqueue/socket\-only event loop in +\&\f(CW\*(C`loop_socket\*(C'\fR. (One might optionally use \f(CW\*(C`EVFLAG_NOENV\*(C'\fR, too). +.PP +.Vb 3 +\& struct ev_loop *loop = ev_default_init (0); +\& struct ev_loop *loop_socket = 0; +\& struct ev_embed embed; +\& +\& if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE) +\& if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE)) +\& { +\& ev_embed_init (&embed, 0, loop_socket); +\& ev_embed_start (loop, &embed); +\& } +\& +\& if (!loop_socket) +\& loop_socket = loop; +\& +\& // now use loop_socket for all sockets, and loop for everything else +.Ve +.ie n .Sh """ev_fork"" \- the audacity to resume the event loop after a fork" +.el .Sh "\f(CWev_fork\fP \- the audacity to resume the event loop after a fork" +.IX Subsection "ev_fork - the audacity to resume the event loop after a fork" +Fork watchers are called when a \f(CW\*(C`fork ()\*(C'\fR was detected (usually because +whoever is a good citizen cared to tell libev about it by calling +\&\f(CW\*(C`ev_default_fork\*(C'\fR or \f(CW\*(C`ev_loop_fork\*(C'\fR). The invocation is done before the +event loop blocks next and before \f(CW\*(C`ev_check\*(C'\fR watchers are being called, +and only in the child after the fork. If whoever good citizen calling +\&\f(CW\*(C`ev_default_fork\*(C'\fR cheats and calls it in the wrong process, the fork +handlers will be invoked, too, of course. +.PP +\fIWatcher-Specific Functions and Data Members\fR +.IX Subsection "Watcher-Specific Functions and Data Members" +.IP "ev_fork_init (ev_signal *, callback)" 4 +.IX Item "ev_fork_init (ev_signal *, callback)" +Initialises and configures the fork watcher \- it has no parameters of any +kind. There is a \f(CW\*(C`ev_fork_set\*(C'\fR macro, but using it is utterly pointless, +believe me. +.ie n .Sh """ev_async"" \- how to wake up another event loop" +.el .Sh "\f(CWev_async\fP \- how to wake up another event loop" +.IX Subsection "ev_async - how to wake up another event loop" +In general, you cannot use an \f(CW\*(C`ev_loop\*(C'\fR from multiple threads or other +asynchronous sources such as signal handlers (as opposed to multiple event +loops \- those are of course safe to use in different threads). +.PP +Sometimes, however, you need to wake up another event loop you do not +control, for example because it belongs to another thread. This is what +\&\f(CW\*(C`ev_async\*(C'\fR watchers do: as long as the \f(CW\*(C`ev_async\*(C'\fR watcher is active, you +can signal it by calling \f(CW\*(C`ev_async_send\*(C'\fR, which is thread\- and signal +safe. +.PP +This functionality is very similar to \f(CW\*(C`ev_signal\*(C'\fR watchers, as signals, +too, are asynchronous in nature, and signals, too, will be compressed +(i.e. the number of callback invocations may be less than the number of +\&\f(CW\*(C`ev_async_sent\*(C'\fR calls). +.PP +Unlike \f(CW\*(C`ev_signal\*(C'\fR watchers, \f(CW\*(C`ev_async\*(C'\fR works with any event loop, not +just the default loop. +.PP +\fIQueueing\fR +.IX Subsection "Queueing" +.PP +\&\f(CW\*(C`ev_async\*(C'\fR does not support queueing of data in any way. The reason +is that the author does not know of a simple (or any) algorithm for a +multiple-writer-single-reader queue that works in all cases and doesn't +need elaborate support such as pthreads. +.PP +That means that if you want to queue data, you have to provide your own +queue. But at least I can tell you would implement locking around your +queue: +.IP "queueing from a signal handler context" 4 +.IX Item "queueing from a signal handler context" +To implement race-free queueing, you simply add to the queue in the signal +handler but you block the signal handler in the watcher callback. Here is an example that does that for +some fictitiuous \s-1SIGUSR1\s0 handler: +.Sp +.Vb 1 +\& static ev_async mysig; +\& +\& static void +\& sigusr1_handler (void) +\& { +\& sometype data; +\& +\& // no locking etc. +\& queue_put (data); +\& ev_async_send (EV_DEFAULT_ &mysig); +\& } +\& +\& static void +\& mysig_cb (EV_P_ ev_async *w, int revents) +\& { +\& sometype data; +\& sigset_t block, prev; +\& +\& sigemptyset (&block); +\& sigaddset (&block, SIGUSR1); +\& sigprocmask (SIG_BLOCK, &block, &prev); +\& +\& while (queue_get (&data)) +\& process (data); +\& +\& if (sigismember (&prev, SIGUSR1) +\& sigprocmask (SIG_UNBLOCK, &block, 0); +\& } +.Ve +.Sp +(Note: pthreads in theory requires you to use \f(CW\*(C`pthread_setmask\*(C'\fR +instead of \f(CW\*(C`sigprocmask\*(C'\fR when you use threads, but libev doesn't do it +either...). +.IP "queueing from a thread context" 4 +.IX Item "queueing from a thread context" +The strategy for threads is different, as you cannot (easily) block +threads but you can easily preempt them, so to queue safely you need to +employ a traditional mutex lock, such as in this pthread example: +.Sp +.Vb 2 +\& static ev_async mysig; +\& static pthread_mutex_t mymutex = PTHREAD_MUTEX_INITIALIZER; +\& +\& static void +\& otherthread (void) +\& { +\& // only need to lock the actual queueing operation +\& pthread_mutex_lock (&mymutex); +\& queue_put (data); +\& pthread_mutex_unlock (&mymutex); +\& +\& ev_async_send (EV_DEFAULT_ &mysig); +\& } +\& +\& static void +\& mysig_cb (EV_P_ ev_async *w, int revents) +\& { +\& pthread_mutex_lock (&mymutex); +\& +\& while (queue_get (&data)) +\& process (data); +\& +\& pthread_mutex_unlock (&mymutex); +\& } +.Ve +.PP +\fIWatcher-Specific Functions and Data Members\fR +.IX Subsection "Watcher-Specific Functions and Data Members" +.IP "ev_async_init (ev_async *, callback)" 4 +.IX Item "ev_async_init (ev_async *, callback)" +Initialises and configures the async watcher \- it has no parameters of any +kind. There is a \f(CW\*(C`ev_asynd_set\*(C'\fR macro, but using it is utterly pointless, +believe me. +.IP "ev_async_send (loop, ev_async *)" 4 +.IX Item "ev_async_send (loop, ev_async *)" +Sends/signals/activates the given \f(CW\*(C`ev_async\*(C'\fR watcher, that is, feeds +an \f(CW\*(C`EV_ASYNC\*(C'\fR event on the watcher into the event loop. Unlike +\&\f(CW\*(C`ev_feed_event\*(C'\fR, this call is safe to do in other threads, signal or +similar contexts (see the dicusssion of \f(CW\*(C`EV_ATOMIC_T\*(C'\fR in the embedding +section below on what exactly this means). +.Sp +This call incurs the overhead of a syscall only once per loop iteration, +so while the overhead might be noticable, it doesn't apply to repeated +calls to \f(CW\*(C`ev_async_send\*(C'\fR. +.IP "bool = ev_async_pending (ev_async *)" 4 +.IX Item "bool = ev_async_pending (ev_async *)" +Returns a non-zero value when \f(CW\*(C`ev_async_send\*(C'\fR has been called on the +watcher but the event has not yet been processed (or even noted) by the +event loop. +.Sp +\&\f(CW\*(C`ev_async_send\*(C'\fR sets a flag in the watcher and wakes up the loop. When +the loop iterates next and checks for the watcher to have become active, +it will reset the flag again. \f(CW\*(C`ev_async_pending\*(C'\fR can be used to very +quickly check wether invoking the loop might be a good idea. +.Sp +Not that this does \fInot\fR check wether the watcher itself is pending, only +wether it has been requested to make this watcher pending. +.SH "OTHER FUNCTIONS" +.IX Header "OTHER FUNCTIONS" +There are some other functions of possible interest. Described. Here. Now. +.IP "ev_once (loop, int fd, int events, ev_tstamp timeout, callback)" 4 +.IX Item "ev_once (loop, int fd, int events, ev_tstamp timeout, callback)" +This function combines a simple timer and an I/O watcher, calls your +callback on whichever event happens first and automatically stop both +watchers. This is useful if you want to wait for a single event on an fd +or timeout without having to allocate/configure/start/stop/free one or +more watchers yourself. +.Sp +If \f(CW\*(C`fd\*(C'\fR is less than 0, then no I/O watcher will be started and events +is being ignored. Otherwise, an \f(CW\*(C`ev_io\*(C'\fR watcher for the given \f(CW\*(C`fd\*(C'\fR and +\&\f(CW\*(C`events\*(C'\fR set will be craeted and started. +.Sp +If \f(CW\*(C`timeout\*(C'\fR is less than 0, then no timeout watcher will be +started. Otherwise an \f(CW\*(C`ev_timer\*(C'\fR watcher with after = \f(CW\*(C`timeout\*(C'\fR (and +repeat = 0) will be started. While \f(CW0\fR is a valid timeout, it is of +dubious value. +.Sp +The callback has the type \f(CW\*(C`void (*cb)(int revents, void *arg)\*(C'\fR and gets +passed an \f(CW\*(C`revents\*(C'\fR set like normal event callbacks (a combination of +\&\f(CW\*(C`EV_ERROR\*(C'\fR, \f(CW\*(C`EV_READ\*(C'\fR, \f(CW\*(C`EV_WRITE\*(C'\fR or \f(CW\*(C`EV_TIMEOUT\*(C'\fR) and the \f(CW\*(C`arg\*(C'\fR +value passed to \f(CW\*(C`ev_once\*(C'\fR: +.Sp +.Vb 7 +\& static void stdin_ready (int revents, void *arg) +\& { +\& if (revents & EV_TIMEOUT) +\& /* doh, nothing entered */; +\& else if (revents & EV_READ) +\& /* stdin might have data for us, joy! */; +\& } +\& +\& ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0); +.Ve +.IP "ev_feed_event (ev_loop *, watcher *, int revents)" 4 +.IX Item "ev_feed_event (ev_loop *, watcher *, int revents)" +Feeds the given event set into the event loop, as if the specified event +had happened for the specified watcher (which must be a pointer to an +initialised but not necessarily started event watcher). +.IP "ev_feed_fd_event (ev_loop *, int fd, int revents)" 4 +.IX Item "ev_feed_fd_event (ev_loop *, int fd, int revents)" +Feed an event on the given fd, as if a file descriptor backend detected +the given events it. +.IP "ev_feed_signal_event (ev_loop *loop, int signum)" 4 +.IX Item "ev_feed_signal_event (ev_loop *loop, int signum)" +Feed an event as if the given signal occured (\f(CW\*(C`loop\*(C'\fR must be the default +loop!). +.SH "LIBEVENT EMULATION" +.IX Header "LIBEVENT EMULATION" +Libev offers a compatibility emulation layer for libevent. It cannot +emulate the internals of libevent, so here are some usage hints: +.IP "\(bu" 4 +Use it by including <event.h>, as usual. +.IP "\(bu" 4 +The following members are fully supported: ev_base, ev_callback, +ev_arg, ev_fd, ev_res, ev_events. +.IP "\(bu" 4 +Avoid using ev_flags and the EVLIST_*\-macros, while it is +maintained by libev, it does not work exactly the same way as in libevent (consider +it a private \s-1API\s0). +.IP "\(bu" 4 +Priorities are not currently supported. Initialising priorities +will fail and all watchers will have the same priority, even though there +is an ev_pri field. +.IP "\(bu" 4 +In libevent, the last base created gets the signals, in libev, the +first base created (== the default loop) gets the signals. +.IP "\(bu" 4 +Other members are not supported. +.IP "\(bu" 4 +The libev emulation is \fInot\fR \s-1ABI\s0 compatible to libevent, you need +to use the libev header file and library. +.SH "\*(C+ SUPPORT" +.IX Header " SUPPORT" +Libev comes with some simplistic wrapper classes for \*(C+ that mainly allow +you to use some convinience methods to start/stop watchers and also change +the callback model to a model using method callbacks on objects. +.PP +To use it, +.PP +.Vb 1 +\& #include <ev++.h> +.Ve +.PP +This automatically includes \fIev.h\fR and puts all of its definitions (many +of them macros) into the global namespace. All \*(C+ specific things are +put into the \f(CW\*(C`ev\*(C'\fR namespace. It should support all the same embedding +options as \fIev.h\fR, most notably \f(CW\*(C`EV_MULTIPLICITY\*(C'\fR. +.PP +Care has been taken to keep the overhead low. The only data member the \*(C+ +classes add (compared to plain C\-style watchers) is the event loop pointer +that the watcher is associated with (or no additional members at all if +you disable \f(CW\*(C`EV_MULTIPLICITY\*(C'\fR when embedding libev). +.PP +Currently, functions, and static and non-static member functions can be +used as callbacks. Other types should be easy to add as long as they only +need one additional pointer for context. If you need support for other +types of functors please contact the author (preferably after implementing +it). +.PP +Here is a list of things available in the \f(CW\*(C`ev\*(C'\fR namespace: +.ie n .IP """ev::READ""\fR, \f(CW""ev::WRITE"" etc." 4 +.el .IP "\f(CWev::READ\fR, \f(CWev::WRITE\fR etc." 4 +.IX Item "ev::READ, ev::WRITE etc." +These are just enum values with the same values as the \f(CW\*(C`EV_READ\*(C'\fR etc. +macros from \fIev.h\fR. +.ie n .IP """ev::tstamp""\fR, \f(CW""ev::now""" 4 +.el .IP "\f(CWev::tstamp\fR, \f(CWev::now\fR" 4 +.IX Item "ev::tstamp, ev::now" +Aliases to the same types/functions as with the \f(CW\*(C`ev_\*(C'\fR prefix. +.ie n .IP """ev::io""\fR, \f(CW""ev::timer""\fR, \f(CW""ev::periodic""\fR, \f(CW""ev::idle""\fR, \f(CW""ev::sig"" etc." 4 +.el .IP "\f(CWev::io\fR, \f(CWev::timer\fR, \f(CWev::periodic\fR, \f(CWev::idle\fR, \f(CWev::sig\fR etc." 4 +.IX Item "ev::io, ev::timer, ev::periodic, ev::idle, ev::sig etc." +For each \f(CW\*(C`ev_TYPE\*(C'\fR watcher in \fIev.h\fR there is a corresponding class of +the same name in the \f(CW\*(C`ev\*(C'\fR namespace, with the exception of \f(CW\*(C`ev_signal\*(C'\fR +which is called \f(CW\*(C`ev::sig\*(C'\fR to avoid clashes with the \f(CW\*(C`signal\*(C'\fR macro +defines by many implementations. +.Sp +All of those classes have these methods: +.RS 4 +.IP "ev::TYPE::TYPE ()" 4 +.IX Item "ev::TYPE::TYPE ()" +.PD 0 +.IP "ev::TYPE::TYPE (struct ev_loop *)" 4 +.IX Item "ev::TYPE::TYPE (struct ev_loop *)" +.IP "ev::TYPE::~TYPE" 4 +.IX Item "ev::TYPE::~TYPE" +.PD +The constructor (optionally) takes an event loop to associate the watcher +with. If it is omitted, it will use \f(CW\*(C`EV_DEFAULT\*(C'\fR. +.Sp +The constructor calls \f(CW\*(C`ev_init\*(C'\fR for you, which means you have to call the +\&\f(CW\*(C`set\*(C'\fR method before starting it. +.Sp +It will not set a callback, however: You have to call the templated \f(CW\*(C`set\*(C'\fR +method to set a callback before you can start the watcher. +.Sp +(The reason why you have to use a method is a limitation in \*(C+ which does +not allow explicit template arguments for constructors). +.Sp +The destructor automatically stops the watcher if it is active. +.IP "w\->set<class, &class::method> (object *)" 4 +.IX Item "w->set<class, &class::method> (object *)" +This method sets the callback method to call. The method has to have a +signature of \f(CW\*(C`void (*)(ev_TYPE &, int)\*(C'\fR, it receives the watcher as +first argument and the \f(CW\*(C`revents\*(C'\fR as second. The object must be given as +parameter and is stored in the \f(CW\*(C`data\*(C'\fR member of the watcher. +.Sp +This method synthesizes efficient thunking code to call your method from +the C callback that libev requires. If your compiler can inline your +callback (i.e. it is visible to it at the place of the \f(CW\*(C`set\*(C'\fR call and +your compiler is good :), then the method will be fully inlined into the +thunking function, making it as fast as a direct C callback. +.Sp +Example: simple class declaration and watcher initialisation +.Sp +.Vb 4 +\& struct myclass +\& { +\& void io_cb (ev::io &w, int revents) { } +\& } +\& +\& myclass obj; +\& ev::io iow; +\& iow.set <myclass, &myclass::io_cb> (&obj); +.Ve +.IP "w\->set<function> (void *data = 0)" 4 +.IX Item "w->set<function> (void *data = 0)" +Also sets a callback, but uses a static method or plain function as +callback. The optional \f(CW\*(C`data\*(C'\fR argument will be stored in the watcher's +\&\f(CW\*(C`data\*(C'\fR member and is free for you to use. +.Sp +The prototype of the \f(CW\*(C`function\*(C'\fR must be \f(CW\*(C`void (*)(ev::TYPE &w, int)\*(C'\fR. +.Sp +See the method\-\f(CW\*(C`set\*(C'\fR above for more details. +.Sp +Example: +.Sp +.Vb 2 +\& static void io_cb (ev::io &w, int revents) { } +\& iow.set <io_cb> (); +.Ve +.IP "w\->set (struct ev_loop *)" 4 +.IX Item "w->set (struct ev_loop *)" +Associates a different \f(CW\*(C`struct ev_loop\*(C'\fR with this watcher. You can only +do this when the watcher is inactive (and not pending either). +.IP "w\->set ([args])" 4 +.IX Item "w->set ([args])" +Basically the same as \f(CW\*(C`ev_TYPE_set\*(C'\fR, with the same args. Must be +called at least once. Unlike the C counterpart, an active watcher gets +automatically stopped and restarted when reconfiguring it with this +method. +.IP "w\->start ()" 4 +.IX Item "w->start ()" +Starts the watcher. Note that there is no \f(CW\*(C`loop\*(C'\fR argument, as the +constructor already stores the event loop. +.IP "w\->stop ()" 4 +.IX Item "w->stop ()" +Stops the watcher if it is active. Again, no \f(CW\*(C`loop\*(C'\fR argument. +.ie n .IP "w\->again () (""ev::timer""\fR, \f(CW""ev::periodic"" only)" 4 +.el .IP "w\->again () (\f(CWev::timer\fR, \f(CWev::periodic\fR only)" 4 +.IX Item "w->again () (ev::timer, ev::periodic only)" +For \f(CW\*(C`ev::timer\*(C'\fR and \f(CW\*(C`ev::periodic\*(C'\fR, this invokes the corresponding +\&\f(CW\*(C`ev_TYPE_again\*(C'\fR function. +.ie n .IP "w\->sweep () (""ev::embed"" only)" 4 +.el .IP "w\->sweep () (\f(CWev::embed\fR only)" 4 +.IX Item "w->sweep () (ev::embed only)" +Invokes \f(CW\*(C`ev_embed_sweep\*(C'\fR. +.ie n .IP "w\->update () (""ev::stat"" only)" 4 +.el .IP "w\->update () (\f(CWev::stat\fR only)" 4 +.IX Item "w->update () (ev::stat only)" +Invokes \f(CW\*(C`ev_stat_stat\*(C'\fR. +.RE +.RS 4 +.RE +.PP +Example: Define a class with an \s-1IO\s0 and idle watcher, start one of them in +the constructor. +.PP +.Vb 4 +\& class myclass +\& { +\& ev::io io; void io_cb (ev::io &w, int revents); +\& ev:idle idle void idle_cb (ev::idle &w, int revents); +\& +\& myclass (int fd) +\& { +\& io .set <myclass, &myclass::io_cb > (this); +\& idle.set <myclass, &myclass::idle_cb> (this); +\& +\& io.start (fd, ev::READ); +\& } +\& }; +.Ve +.SH "OTHER LANGUAGE BINDINGS" +.IX Header "OTHER LANGUAGE BINDINGS" +Libev does not offer other language bindings itself, but bindings for a +numbe rof languages exist in the form of third-party packages. If you know +any interesting language binding in addition to the ones listed here, drop +me a note. +.IP "Perl" 4 +.IX Item "Perl" +The \s-1EV\s0 module implements the full libev \s-1API\s0 and is actually used to test +libev. \s-1EV\s0 is developed together with libev. Apart from the \s-1EV\s0 core module, +there are additional modules that implement libev-compatible interfaces +to \f(CW\*(C`libadns\*(C'\fR (\f(CW\*(C`EV::ADNS\*(C'\fR), \f(CW\*(C`Net::SNMP\*(C'\fR (\f(CW\*(C`Net::SNMP::EV\*(C'\fR) and the +\&\f(CW\*(C`libglib\*(C'\fR event core (\f(CW\*(C`Glib::EV\*(C'\fR and \f(CW\*(C`EV::Glib\*(C'\fR). +.Sp +It can be found and installed via \s-1CPAN\s0, its homepage is found at +<http://software.schmorp.de/pkg/EV>. +.IP "Ruby" 4 +.IX Item "Ruby" +Tony Arcieri has written a ruby extension that offers access to a subset +of the libev \s-1API\s0 and adds filehandle abstractions, asynchronous \s-1DNS\s0 and +more on top of it. It can be found via gem servers. Its homepage is at +<http://rev.rubyforge.org/>. +.IP "D" 4 +.IX Item "D" +Leandro Lucarella has written a D language binding (\fIev.d\fR) for libev, to +be found at <http://git.llucax.com.ar/?p=software/ev.d.git;a=summary>. +.SH "MACRO MAGIC" +.IX Header "MACRO MAGIC" +Libev can be compiled with a variety of options, the most fundamantal +of which is \f(CW\*(C`EV_MULTIPLICITY\*(C'\fR. This option determines whether (most) +functions and callbacks have an initial \f(CW\*(C`struct ev_loop *\*(C'\fR argument. +.PP +To make it easier to write programs that cope with either variant, the +following macros are defined: +.ie n .IP """EV_A""\fR, \f(CW""EV_A_""" 4 +.el .IP "\f(CWEV_A\fR, \f(CWEV_A_\fR" 4 +.IX Item "EV_A, EV_A_" +This provides the loop \fIargument\fR for functions, if one is required (\*(L"ev +loop argument\*(R"). The \f(CW\*(C`EV_A\*(C'\fR form is used when this is the sole argument, +\&\f(CW\*(C`EV_A_\*(C'\fR is used when other arguments are following. Example: +.Sp +.Vb 3 +\& ev_unref (EV_A); +\& ev_timer_add (EV_A_ watcher); +\& ev_loop (EV_A_ 0); +.Ve +.Sp +It assumes the variable \f(CW\*(C`loop\*(C'\fR of type \f(CW\*(C`struct ev_loop *\*(C'\fR is in scope, +which is often provided by the following macro. +.ie n .IP """EV_P""\fR, \f(CW""EV_P_""" 4 +.el .IP "\f(CWEV_P\fR, \f(CWEV_P_\fR" 4 +.IX Item "EV_P, EV_P_" +This provides the loop \fIparameter\fR for functions, if one is required (\*(L"ev +loop parameter\*(R"). The \f(CW\*(C`EV_P\*(C'\fR form is used when this is the sole parameter, +\&\f(CW\*(C`EV_P_\*(C'\fR is used when other parameters are following. Example: +.Sp +.Vb 2 +\& // this is how ev_unref is being declared +\& static void ev_unref (EV_P); +\& +\& // this is how you can declare your typical callback +\& static void cb (EV_P_ ev_timer *w, int revents) +.Ve +.Sp +It declares a parameter \f(CW\*(C`loop\*(C'\fR of type \f(CW\*(C`struct ev_loop *\*(C'\fR, quite +suitable for use with \f(CW\*(C`EV_A\*(C'\fR. +.ie n .IP """EV_DEFAULT""\fR, \f(CW""EV_DEFAULT_""" 4 +.el .IP "\f(CWEV_DEFAULT\fR, \f(CWEV_DEFAULT_\fR" 4 +.IX Item "EV_DEFAULT, EV_DEFAULT_" +Similar to the other two macros, this gives you the value of the default +loop, if multiple loops are supported (\*(L"ev loop default\*(R"). +.ie n .IP """EV_DEFAULT_UC""\fR, \f(CW""EV_DEFAULT_UC_""" 4 +.el .IP "\f(CWEV_DEFAULT_UC\fR, \f(CWEV_DEFAULT_UC_\fR" 4 +.IX Item "EV_DEFAULT_UC, EV_DEFAULT_UC_" +Usage identical to \f(CW\*(C`EV_DEFAULT\*(C'\fR and \f(CW\*(C`EV_DEFAULT_\*(C'\fR, but requires that the +default loop has been initialised (\f(CW\*(C`UC\*(C'\fR == unchecked). Their behaviour +is undefined when the default loop has not been initialised by a previous +execution of \f(CW\*(C`EV_DEFAULT\*(C'\fR, \f(CW\*(C`EV_DEFAULT_\*(C'\fR or \f(CW\*(C`ev_default_init (...)\*(C'\fR. +.Sp +It is often prudent to use \f(CW\*(C`EV_DEFAULT\*(C'\fR when initialising the first +watcher in a function but use \f(CW\*(C`EV_DEFAULT_UC\*(C'\fR afterwards. +.PP +Example: Declare and initialise a check watcher, utilising the above +macros so it will work regardless of whether multiple loops are supported +or not. +.PP +.Vb 5 +\& static void +\& check_cb (EV_P_ ev_timer *w, int revents) +\& { +\& ev_check_stop (EV_A_ w); +\& } +\& +\& ev_check check; +\& ev_check_init (&check, check_cb); +\& ev_check_start (EV_DEFAULT_ &check); +\& ev_loop (EV_DEFAULT_ 0); +.Ve +.SH "EMBEDDING" +.IX Header "EMBEDDING" +Libev can (and often is) directly embedded into host +applications. Examples of applications that embed it include the Deliantra +Game Server, the \s-1EV\s0 perl module, the \s-1GNU\s0 Virtual Private Ethernet (gvpe) +and rxvt-unicode. +.PP +The goal is to enable you to just copy the necessary files into your +source directory without having to change even a single line in them, so +you can easily upgrade by simply copying (or having a checked-out copy of +libev somewhere in your source tree). +.Sh "\s-1FILESETS\s0" +.IX Subsection "FILESETS" +Depending on what features you need you need to include one or more sets of files +in your app. +.PP +\fI\s-1CORE\s0 \s-1EVENT\s0 \s-1LOOP\s0\fR +.IX Subsection "CORE EVENT LOOP" +.PP +To include only the libev core (all the \f(CW\*(C`ev_*\*(C'\fR functions), with manual +configuration (no autoconf): +.PP +.Vb 2 +\& #define EV_STANDALONE 1 +\& #include "ev.c" +.Ve +.PP +This will automatically include \fIev.h\fR, too, and should be done in a +single C source file only to provide the function implementations. To use +it, do the same for \fIev.h\fR in all files wishing to use this \s-1API\s0 (best +done by writing a wrapper around \fIev.h\fR that you can include instead and +where you can put other configuration options): +.PP +.Vb 2 +\& #define EV_STANDALONE 1 +\& #include "ev.h" +.Ve +.PP +Both header files and implementation files can be compiled with a \*(C+ +compiler (at least, thats a stated goal, and breakage will be treated +as a bug). +.PP +You need the following files in your source tree, or in a directory +in your include path (e.g. in libev/ when using \-Ilibev): +.PP +.Vb 4 +\& ev.h +\& ev.c +\& ev_vars.h +\& ev_wrap.h +\& +\& ev_win32.c required on win32 platforms only +\& +\& ev_select.c only when select backend is enabled (which is enabled by default) +\& ev_poll.c only when poll backend is enabled (disabled by default) +\& ev_epoll.c only when the epoll backend is enabled (disabled by default) +\& ev_kqueue.c only when the kqueue backend is enabled (disabled by default) +\& ev_port.c only when the solaris port backend is enabled (disabled by default) +.Ve +.PP +\&\fIev.c\fR includes the backend files directly when enabled, so you only need +to compile this single file. +.PP +\fI\s-1LIBEVENT\s0 \s-1COMPATIBILITY\s0 \s-1API\s0\fR +.IX Subsection "LIBEVENT COMPATIBILITY API" +.PP +To include the libevent compatibility \s-1API\s0, also include: +.PP +.Vb 1 +\& #include "event.c" +.Ve +.PP +in the file including \fIev.c\fR, and: +.PP +.Vb 1 +\& #include "event.h" +.Ve +.PP +in the files that want to use the libevent \s-1API\s0. This also includes \fIev.h\fR. +.PP +You need the following additional files for this: +.PP +.Vb 2 +\& event.h +\& event.c +.Ve +.PP +\fI\s-1AUTOCONF\s0 \s-1SUPPORT\s0\fR +.IX Subsection "AUTOCONF SUPPORT" +.PP +Instead of using \f(CW\*(C`EV_STANDALONE=1\*(C'\fR and providing your config in +whatever way you want, you can also \f(CW\*(C`m4_include([libev.m4])\*(C'\fR in your +\&\fIconfigure.ac\fR and leave \f(CW\*(C`EV_STANDALONE\*(C'\fR undefined. \fIev.c\fR will then +include \fIconfig.h\fR and configure itself accordingly. +.PP +For this of course you need the m4 file: +.PP +.Vb 1 +\& libev.m4 +.Ve +.Sh "\s-1PREPROCESSOR\s0 \s-1SYMBOLS/MACROS\s0" +.IX Subsection "PREPROCESSOR SYMBOLS/MACROS" +Libev can be configured via a variety of preprocessor symbols you have to +define before including any of its files. The default in the absense of +autoconf is noted for every option. +.IP "\s-1EV_STANDALONE\s0" 4 +.IX Item "EV_STANDALONE" +Must always be \f(CW1\fR if you do not use autoconf configuration, which +keeps libev from including \fIconfig.h\fR, and it also defines dummy +implementations for some libevent functions (such as logging, which is not +supported). It will also not define any of the structs usually found in +\&\fIevent.h\fR that are not directly supported by the libev core alone. +.IP "\s-1EV_USE_MONOTONIC\s0" 4 +.IX Item "EV_USE_MONOTONIC" +If defined to be \f(CW1\fR, libev will try to detect the availability of the +monotonic clock option at both compiletime and runtime. Otherwise no use +of the monotonic clock option will be attempted. If you enable this, you +usually have to link against librt or something similar. Enabling it when +the functionality isn't available is safe, though, although you have +to make sure you link against any libraries where the \f(CW\*(C`clock_gettime\*(C'\fR +function is hiding in (often \fI\-lrt\fR). +.IP "\s-1EV_USE_REALTIME\s0" 4 +.IX Item "EV_USE_REALTIME" +If defined to be \f(CW1\fR, libev will try to detect the availability of the +realtime clock option at compiletime (and assume its availability at +runtime if successful). Otherwise no use of the realtime clock option will +be attempted. This effectively replaces \f(CW\*(C`gettimeofday\*(C'\fR by \f(CW\*(C`clock_get +(CLOCK_REALTIME, ...)\*(C'\fR and will not normally affect correctness. See the +note about libraries in the description of \f(CW\*(C`EV_USE_MONOTONIC\*(C'\fR, though. +.IP "\s-1EV_USE_NANOSLEEP\s0" 4 +.IX Item "EV_USE_NANOSLEEP" +If defined to be \f(CW1\fR, libev will assume that \f(CW\*(C`nanosleep ()\*(C'\fR is available +and will use it for delays. Otherwise it will use \f(CW\*(C`select ()\*(C'\fR. +.IP "\s-1EV_USE_EVENTFD\s0" 4 +.IX Item "EV_USE_EVENTFD" +If defined to be \f(CW1\fR, then libev will assume that \f(CW\*(C`eventfd ()\*(C'\fR is +available and will probe for kernel support at runtime. This will improve +\&\f(CW\*(C`ev_signal\*(C'\fR and \f(CW\*(C`ev_async\*(C'\fR performance and reduce resource consumption. +If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc +2.7 or newer, otherwise disabled. +.IP "\s-1EV_USE_SELECT\s0" 4 +.IX Item "EV_USE_SELECT" +If undefined or defined to be \f(CW1\fR, libev will compile in support for the +\&\f(CW\*(C`select\*(C'\fR(2) backend. No attempt at autodetection will be done: if no +other method takes over, select will be it. Otherwise the select backend +will not be compiled in. +.IP "\s-1EV_SELECT_USE_FD_SET\s0" 4 +.IX Item "EV_SELECT_USE_FD_SET" +If defined to \f(CW1\fR, then the select backend will use the system \f(CW\*(C`fd_set\*(C'\fR +structure. This is useful if libev doesn't compile due to a missing +\&\f(CW\*(C`NFDBITS\*(C'\fR or \f(CW\*(C`fd_mask\*(C'\fR definition or it misguesses the bitset layout on +exotic systems. This usually limits the range of file descriptors to some +low limit such as 1024 or might have other limitations (winsocket only +allows 64 sockets). The \f(CW\*(C`FD_SETSIZE\*(C'\fR macro, set before compilation, might +influence the size of the \f(CW\*(C`fd_set\*(C'\fR used. +.IP "\s-1EV_SELECT_IS_WINSOCKET\s0" 4 +.IX Item "EV_SELECT_IS_WINSOCKET" +When defined to \f(CW1\fR, the select backend will assume that +select/socket/connect etc. don't understand file descriptors but +wants osf handles on win32 (this is the case when the select to +be used is the winsock select). This means that it will call +\&\f(CW\*(C`_get_osfhandle\*(C'\fR on the fd to convert it to an \s-1OS\s0 handle. Otherwise, +it is assumed that all these functions actually work on fds, even +on win32. Should not be defined on non\-win32 platforms. +.IP "\s-1EV_FD_TO_WIN32_HANDLE\s0" 4 +.IX Item "EV_FD_TO_WIN32_HANDLE" +If \f(CW\*(C`EV_SELECT_IS_WINSOCKET\*(C'\fR is enabled, then libev needs a way to map +file descriptors to socket handles. When not defining this symbol (the +default), then libev will call \f(CW\*(C`_get_osfhandle\*(C'\fR, which is usually +correct. In some cases, programs use their own file descriptor management, +in which case they can provide this function to map fds to socket handles. +.IP "\s-1EV_USE_POLL\s0" 4 +.IX Item "EV_USE_POLL" +If defined to be \f(CW1\fR, libev will compile in support for the \f(CW\*(C`poll\*(C'\fR(2) +backend. Otherwise it will be enabled on non\-win32 platforms. It +takes precedence over select. +.IP "\s-1EV_USE_EPOLL\s0" 4 +.IX Item "EV_USE_EPOLL" +If defined to be \f(CW1\fR, libev will compile in support for the Linux +\&\f(CW\*(C`epoll\*(C'\fR(7) backend. Its availability will be detected at runtime, +otherwise another method will be used as fallback. This is the preferred +backend for GNU/Linux systems. If undefined, it will be enabled if the +headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled. +.IP "\s-1EV_USE_KQUEUE\s0" 4 +.IX Item "EV_USE_KQUEUE" +If defined to be \f(CW1\fR, libev will compile in support for the \s-1BSD\s0 style +\&\f(CW\*(C`kqueue\*(C'\fR(2) backend. Its actual availability will be detected at runtime, +otherwise another method will be used as fallback. This is the preferred +backend for \s-1BSD\s0 and BSD-like systems, although on most BSDs kqueue only +supports some types of fds correctly (the only platform we found that +supports ptys for example was NetBSD), so kqueue might be compiled in, but +not be used unless explicitly requested. The best way to use it is to find +out whether kqueue supports your type of fd properly and use an embedded +kqueue loop. +.IP "\s-1EV_USE_PORT\s0" 4 +.IX Item "EV_USE_PORT" +If defined to be \f(CW1\fR, libev will compile in support for the Solaris +10 port style backend. Its availability will be detected at runtime, +otherwise another method will be used as fallback. This is the preferred +backend for Solaris 10 systems. +.IP "\s-1EV_USE_DEVPOLL\s0" 4 +.IX Item "EV_USE_DEVPOLL" +reserved for future expansion, works like the \s-1USE\s0 symbols above. +.IP "\s-1EV_USE_INOTIFY\s0" 4 +.IX Item "EV_USE_INOTIFY" +If defined to be \f(CW1\fR, libev will compile in support for the Linux inotify +interface to speed up \f(CW\*(C`ev_stat\*(C'\fR watchers. Its actual availability will +be detected at runtime. If undefined, it will be enabled if the headers +indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled. +.IP "\s-1EV_ATOMIC_T\s0" 4 +.IX Item "EV_ATOMIC_T" +Libev requires an integer type (suitable for storing \f(CW0\fR or \f(CW1\fR) whose +access is atomic with respect to other threads or signal contexts. No such +type is easily found in the C language, so you can provide your own type +that you know is safe for your purposes. It is used both for signal handler \*(L"locking\*(R" +as well as for signal and thread safety in \f(CW\*(C`ev_async\*(C'\fR watchers. +.Sp +In the absense of this define, libev will use \f(CW\*(C`sig_atomic_t volatile\*(C'\fR +(from \fIsignal.h\fR), which is usually good enough on most platforms. +.IP "\s-1EV_H\s0" 4 +.IX Item "EV_H" +The name of the \fIev.h\fR header file used to include it. The default if +undefined is \f(CW"ev.h"\fR in \fIevent.h\fR, \fIev.c\fR and \fIev++.h\fR. This can be +used to virtually rename the \fIev.h\fR header file in case of conflicts. +.IP "\s-1EV_CONFIG_H\s0" 4 +.IX Item "EV_CONFIG_H" +If \f(CW\*(C`EV_STANDALONE\*(C'\fR isn't \f(CW1\fR, this variable can be used to override +\&\fIev.c\fR's idea of where to find the \fIconfig.h\fR file, similarly to +\&\f(CW\*(C`EV_H\*(C'\fR, above. +.IP "\s-1EV_EVENT_H\s0" 4 +.IX Item "EV_EVENT_H" +Similarly to \f(CW\*(C`EV_H\*(C'\fR, this macro can be used to override \fIevent.c\fR's idea +of how the \fIevent.h\fR header can be found, the default is \f(CW"event.h"\fR. +.IP "\s-1EV_PROTOTYPES\s0" 4 +.IX Item "EV_PROTOTYPES" +If defined to be \f(CW0\fR, then \fIev.h\fR will not define any function +prototypes, but still define all the structs and other symbols. This is +occasionally useful if you want to provide your own wrapper functions +around libev functions. +.IP "\s-1EV_MULTIPLICITY\s0" 4 +.IX Item "EV_MULTIPLICITY" +If undefined or defined to \f(CW1\fR, then all event-loop-specific functions +will have the \f(CW\*(C`struct ev_loop *\*(C'\fR as first argument, and you can create +additional independent event loops. Otherwise there will be no support +for multiple event loops and there is no first event loop pointer +argument. Instead, all functions act on the single default loop. +.IP "\s-1EV_MINPRI\s0" 4 +.IX Item "EV_MINPRI" +.PD 0 +.IP "\s-1EV_MAXPRI\s0" 4 +.IX Item "EV_MAXPRI" +.PD +The range of allowed priorities. \f(CW\*(C`EV_MINPRI\*(C'\fR must be smaller or equal to +\&\f(CW\*(C`EV_MAXPRI\*(C'\fR, but otherwise there are no non-obvious limitations. You can +provide for more priorities by overriding those symbols (usually defined +to be \f(CW\*(C`\-2\*(C'\fR and \f(CW2\fR, respectively). +.Sp +When doing priority-based operations, libev usually has to linearly search +all the priorities, so having many of them (hundreds) uses a lot of space +and time, so using the defaults of five priorities (\-2 .. +2) is usually +fine. +.Sp +If your embedding app does not need any priorities, defining these both to +\&\f(CW0\fR will save some memory and cpu. +.IP "\s-1EV_PERIODIC_ENABLE\s0" 4 +.IX Item "EV_PERIODIC_ENABLE" +If undefined or defined to be \f(CW1\fR, then periodic timers are supported. If +defined to be \f(CW0\fR, then they are not. Disabling them saves a few kB of +code. +.IP "\s-1EV_IDLE_ENABLE\s0" 4 +.IX Item "EV_IDLE_ENABLE" +If undefined or defined to be \f(CW1\fR, then idle watchers are supported. If +defined to be \f(CW0\fR, then they are not. Disabling them saves a few kB of +code. +.IP "\s-1EV_EMBED_ENABLE\s0" 4 +.IX Item "EV_EMBED_ENABLE" +If undefined or defined to be \f(CW1\fR, then embed watchers are supported. If +defined to be \f(CW0\fR, then they are not. +.IP "\s-1EV_STAT_ENABLE\s0" 4 +.IX Item "EV_STAT_ENABLE" +If undefined or defined to be \f(CW1\fR, then stat watchers are supported. If +defined to be \f(CW0\fR, then they are not. +.IP "\s-1EV_FORK_ENABLE\s0" 4 +.IX Item "EV_FORK_ENABLE" +If undefined or defined to be \f(CW1\fR, then fork watchers are supported. If +defined to be \f(CW0\fR, then they are not. +.IP "\s-1EV_ASYNC_ENABLE\s0" 4 +.IX Item "EV_ASYNC_ENABLE" +If undefined or defined to be \f(CW1\fR, then async watchers are supported. If +defined to be \f(CW0\fR, then they are not. +.IP "\s-1EV_MINIMAL\s0" 4 +.IX Item "EV_MINIMAL" +If you need to shave off some kilobytes of code at the expense of some +speed, define this symbol to \f(CW1\fR. Currently this is used to override some +inlining decisions, saves roughly 30% codesize of amd64. It also selects a +much smaller 2\-heap for timer management over the default 4\-heap. +.IP "\s-1EV_PID_HASHSIZE\s0" 4 +.IX Item "EV_PID_HASHSIZE" +\&\f(CW\*(C`ev_child\*(C'\fR watchers use a small hash table to distribute workload by +pid. The default size is \f(CW16\fR (or \f(CW1\fR with \f(CW\*(C`EV_MINIMAL\*(C'\fR), usually more +than enough. If you need to manage thousands of children you might want to +increase this value (\fImust\fR be a power of two). +.IP "\s-1EV_INOTIFY_HASHSIZE\s0" 4 +.IX Item "EV_INOTIFY_HASHSIZE" +\&\f(CW\*(C`ev_stat\*(C'\fR watchers use a small hash table to distribute workload by +inotify watch id. The default size is \f(CW16\fR (or \f(CW1\fR with \f(CW\*(C`EV_MINIMAL\*(C'\fR), +usually more than enough. If you need to manage thousands of \f(CW\*(C`ev_stat\*(C'\fR +watchers you might want to increase this value (\fImust\fR be a power of +two). +.IP "\s-1EV_USE_4HEAP\s0" 4 +.IX Item "EV_USE_4HEAP" +Heaps are not very cache-efficient. To improve the cache-efficiency of the +timer and periodics heap, libev uses a 4\-heap when this symbol is defined +to \f(CW1\fR. The 4\-heap uses more complicated (longer) code but has a +noticable after performance with many (thousands) of watchers. +.Sp +The default is \f(CW1\fR unless \f(CW\*(C`EV_MINIMAL\*(C'\fR is set in which case it is \f(CW0\fR +(disabled). +.IP "\s-1EV_HEAP_CACHE_AT\s0" 4 +.IX Item "EV_HEAP_CACHE_AT" +Heaps are not very cache-efficient. To improve the cache-efficiency of the +timer and periodics heap, libev can cache the timestamp (\fIat\fR) within +the heap structure (selected by defining \f(CW\*(C`EV_HEAP_CACHE_AT\*(C'\fR to \f(CW1\fR), +which uses 8\-12 bytes more per watcher and a few hundred bytes more code, +but avoids random read accesses on heap changes. This noticably improves +performance noticably with with many (hundreds) of watchers. +.Sp +The default is \f(CW1\fR unless \f(CW\*(C`EV_MINIMAL\*(C'\fR is set in which case it is \f(CW0\fR +(disabled). +.IP "\s-1EV_COMMON\s0" 4 +.IX Item "EV_COMMON" +By default, all watchers have a \f(CW\*(C`void *data\*(C'\fR member. By redefining +this macro to a something else you can include more and other types of +members. You have to define it each time you include one of the files, +though, and it must be identical each time. +.Sp +For example, the perl \s-1EV\s0 module uses something like this: +.Sp +.Vb 3 +\& #define EV_COMMON \e +\& SV *self; /* contains this struct */ \e +\& SV *cb_sv, *fh /* note no trailing ";" */ +.Ve +.IP "\s-1EV_CB_DECLARE\s0 (type)" 4 +.IX Item "EV_CB_DECLARE (type)" +.PD 0 +.IP "\s-1EV_CB_INVOKE\s0 (watcher, revents)" 4 +.IX Item "EV_CB_INVOKE (watcher, revents)" +.IP "ev_set_cb (ev, cb)" 4 +.IX Item "ev_set_cb (ev, cb)" +.PD +Can be used to change the callback member declaration in each watcher, +and the way callbacks are invoked and set. Must expand to a struct member +definition and a statement, respectively. See the \fIev.h\fR header file for +their default definitions. One possible use for overriding these is to +avoid the \f(CW\*(C`struct ev_loop *\*(C'\fR as first argument in all cases, or to use +method calls instead of plain function calls in \*(C+. +.Sh "\s-1EXPORTED\s0 \s-1API\s0 \s-1SYMBOLS\s0" +.IX Subsection "EXPORTED API SYMBOLS" +If you need to re-export the \s-1API\s0 (e.g. via a dll) and you need a list of +exported symbols, you can use the provided \fISymbol.*\fR files which list +all public symbols, one per line: +.PP +.Vb 2 +\& Symbols.ev for libev proper +\& Symbols.event for the libevent emulation +.Ve +.PP +This can also be used to rename all public symbols to avoid clashes with +multiple versions of libev linked together (which is obviously bad in +itself, but sometimes it is inconvinient to avoid this). +.PP +A sed command like this will create wrapper \f(CW\*(C`#define\*(C'\fR's that you need to +include before including \fIev.h\fR: +.PP +.Vb 1 +\& <Symbols.ev sed \-e "s/.*/#define & myprefix_&/" >wrap.h +.Ve +.PP +This would create a file \fIwrap.h\fR which essentially looks like this: +.PP +.Vb 4 +\& #define ev_backend myprefix_ev_backend +\& #define ev_check_start myprefix_ev_check_start +\& #define ev_check_stop myprefix_ev_check_stop +\& ... +.Ve +.Sh "\s-1EXAMPLES\s0" +.IX Subsection "EXAMPLES" +For a real-world example of a program the includes libev +verbatim, you can have a look at the \s-1EV\s0 perl module +(<http://software.schmorp.de/pkg/EV.html>). It has the libev files in +the \fIlibev/\fR subdirectory and includes them in the \fI\s-1EV/EVAPI\s0.h\fR (public +interface) and \fI\s-1EV\s0.xs\fR (implementation) files. Only the \fI\s-1EV\s0.xs\fR file +will be compiled. It is pretty complex because it provides its own header +file. +.PP +The usage in rxvt-unicode is simpler. It has a \fIev_cpp.h\fR header file +that everybody includes and which overrides some configure choices: +.PP +.Vb 9 +\& #define EV_MINIMAL 1 +\& #define EV_USE_POLL 0 +\& #define EV_MULTIPLICITY 0 +\& #define EV_PERIODIC_ENABLE 0 +\& #define EV_STAT_ENABLE 0 +\& #define EV_FORK_ENABLE 0 +\& #define EV_CONFIG_H <config.h> +\& #define EV_MINPRI 0 +\& #define EV_MAXPRI 0 +\& +\& #include "ev++.h" +.Ve +.PP +And a \fIev_cpp.C\fR implementation file that contains libev proper and is compiled: +.PP +.Vb 2 +\& #include "ev_cpp.h" +\& #include "ev.c" +.Ve +.SH "THREADS AND COROUTINES" +.IX Header "THREADS AND COROUTINES" +.Sh "\s-1THREADS\s0" +.IX Subsection "THREADS" +Libev itself is completely threadsafe, but it uses no locking. This +means that you can use as many loops as you want in parallel, as long as +only one thread ever calls into one libev function with the same loop +parameter. +.PP +Or put differently: calls with different loop parameters can be done in +parallel from multiple threads, calls with the same loop parameter must be +done serially (but can be done from different threads, as long as only one +thread ever is inside a call at any point in time, e.g. by using a mutex +per loop). +.PP +If you want to know which design is best for your problem, then I cannot +help you but by giving some generic advice: +.IP "\(bu" 4 +most applications have a main thread: use the default libev loop +in that thread, or create a seperate thread running only the default loop. +.Sp +This helps integrating other libraries or software modules that use libev +themselves and don't care/know about threading. +.IP "\(bu" 4 +one loop per thread is usually a good model. +.Sp +Doing this is almost never wrong, sometimes a better-performance model +exists, but it is always a good start. +.IP "\(bu" 4 +other models exist, such as the leader/follower pattern, where one +loop is handed through multiple threads in a kind of round-robbin fashion. +.Sp +Chosing a model is hard \- look around, learn, know that usually you cna do +better than you currently do :\-) +.IP "\(bu" 4 +often you need to talk to some other thread which blocks in the +event loop \- \f(CW\*(C`ev_async\*(C'\fR watchers can be used to wake them up from other +threads safely (or from signal contexts...). +.Sh "\s-1COROUTINES\s0" +.IX Subsection "COROUTINES" +Libev is much more accomodating to coroutines (\*(L"cooperative threads\*(R"): +libev fully supports nesting calls to it's functions from different +coroutines (e.g. you can call \f(CW\*(C`ev_loop\*(C'\fR on the same loop from two +different coroutines and switch freely between both coroutines running the +loop, as long as you don't confuse yourself). The only exception is that +you must not do this from \f(CW\*(C`ev_periodic\*(C'\fR reschedule callbacks. +.PP +Care has been invested into making sure that libev does not keep local +state inside \f(CW\*(C`ev_loop\*(C'\fR, and other calls do not usually allow coroutine +switches. +.SH "COMPLEXITIES" +.IX Header "COMPLEXITIES" +In this section the complexities of (many of) the algorithms used inside +libev will be explained. For complexity discussions about backends see the +documentation for \f(CW\*(C`ev_default_init\*(C'\fR. +.PP +All of the following are about amortised time: If an array needs to be +extended, libev needs to realloc and move the whole array, but this +happens asymptotically never with higher number of elements, so O(1) might +mean it might do a lengthy realloc operation in rare cases, but on average +it is much faster and asymptotically approaches constant time. +.IP "Starting and stopping timer/periodic watchers: O(log skipped_other_timers)" 4 +.IX Item "Starting and stopping timer/periodic watchers: O(log skipped_other_timers)" +This means that, when you have a watcher that triggers in one hour and +there are 100 watchers that would trigger before that then inserting will +have to skip roughly seven (\f(CW\*(C`ld 100\*(C'\fR) of these watchers. +.IP "Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)" 4 +.IX Item "Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)" +That means that changing a timer costs less than removing/adding them +as only the relative motion in the event queue has to be paid for. +.IP "Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)" 4 +.IX Item "Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)" +These just add the watcher into an array or at the head of a list. +.IP "Stopping check/prepare/idle/fork/async watchers: O(1)" 4 +.IX Item "Stopping check/prepare/idle/fork/async watchers: O(1)" +.PD 0 +.IP "Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % \s-1EV_PID_HASHSIZE\s0))" 4 +.IX Item "Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))" +.PD +These watchers are stored in lists then need to be walked to find the +correct watcher to remove. The lists are usually short (you don't usually +have many watchers waiting for the same fd or signal). +.IP "Finding the next timer in each loop iteration: O(1)" 4 +.IX Item "Finding the next timer in each loop iteration: O(1)" +By virtue of using a binary or 4\-heap, the next timer is always found at a +fixed position in the storage array. +.IP "Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)" 4 +.IX Item "Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)" +A change means an I/O watcher gets started or stopped, which requires +libev to recalculate its status (and possibly tell the kernel, depending +on backend and wether \f(CW\*(C`ev_io_set\*(C'\fR was used). +.IP "Activating one watcher (putting it into the pending state): O(1)" 4 +.IX Item "Activating one watcher (putting it into the pending state): O(1)" +.PD 0 +.IP "Priority handling: O(number_of_priorities)" 4 +.IX Item "Priority handling: O(number_of_priorities)" +.PD +Priorities are implemented by allocating some space for each +priority. When doing priority-based operations, libev usually has to +linearly search all the priorities, but starting/stopping and activating +watchers becomes O(1) w.r.t. priority handling. +.IP "Sending an ev_async: O(1)" 4 +.IX Item "Sending an ev_async: O(1)" +.PD 0 +.IP "Processing ev_async_send: O(number_of_async_watchers)" 4 +.IX Item "Processing ev_async_send: O(number_of_async_watchers)" +.IP "Processing signals: O(max_signal_number)" 4 +.IX Item "Processing signals: O(max_signal_number)" +.PD +Sending involves a syscall \fIiff\fR there were no other \f(CW\*(C`ev_async_send\*(C'\fR +calls in the current loop iteration. Checking for async and signal events +involves iterating over all running async watchers or all signal numbers. +.SH "Win32 platform limitations and workarounds" +.IX Header "Win32 platform limitations and workarounds" +Win32 doesn't support any of the standards (e.g. \s-1POSIX\s0) that libev +requires, and its I/O model is fundamentally incompatible with the \s-1POSIX\s0 +model. Libev still offers limited functionality on this platform in +the form of the \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR backend, and only supports socket +descriptors. This only applies when using Win32 natively, not when using +e.g. cygwin. +.PP +Lifting these limitations would basically require the full +re-implementation of the I/O system. If you are into these kinds of +things, then note that glib does exactly that for you in a very portable +way (note also that glib is the slowest event library known to man). +.PP +There is no supported compilation method available on windows except +embedding it into other applications. +.PP +Due to the many, low, and arbitrary limits on the win32 platform and +the abysmal performance of winsockets, using a large number of sockets +is not recommended (and not reasonable). If your program needs to use +more than a hundred or so sockets, then likely it needs to use a totally +different implementation for windows, as libev offers the \s-1POSIX\s0 readyness +notification model, which cannot be implemented efficiently on windows +(microsoft monopoly games). +.IP "The winsocket select function" 4 +.IX Item "The winsocket select function" +The winsocket \f(CW\*(C`select\*(C'\fR function doesn't follow \s-1POSIX\s0 in that it requires +socket \fIhandles\fR and not socket \fIfile descriptors\fR. This makes select +very inefficient, and also requires a mapping from file descriptors +to socket handles. See the discussion of the \f(CW\*(C`EV_SELECT_USE_FD_SET\*(C'\fR, +\&\f(CW\*(C`EV_SELECT_IS_WINSOCKET\*(C'\fR and \f(CW\*(C`EV_FD_TO_WIN32_HANDLE\*(C'\fR preprocessor +symbols for more info. +.Sp +The configuration for a \*(L"naked\*(R" win32 using the microsoft runtime +libraries and raw winsocket select is: +.Sp +.Vb 2 +\& #define EV_USE_SELECT 1 +\& #define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */ +.Ve +.Sp +Note that winsockets handling of fd sets is O(n), so you can easily get a +complexity in the O(nA\*^X) range when using win32. +.IP "Limited number of file descriptors" 4 +.IX Item "Limited number of file descriptors" +Windows has numerous arbitrary (and low) limits on things. +.Sp +Early versions of winsocket's select only supported waiting for a maximum +of \f(CW64\fR handles (probably owning to the fact that all windows kernels +can only wait for \f(CW64\fR things at the same time internally; microsoft +recommends spawning a chain of threads and wait for 63 handles and the +previous thread in each. Great). +.Sp +Newer versions support more handles, but you need to define \f(CW\*(C`FD_SETSIZE\*(C'\fR +to some high number (e.g. \f(CW2048\fR) before compiling the winsocket select +call (which might be in libev or elsewhere, for example, perl does its own +select emulation on windows). +.Sp +Another limit is the number of file descriptors in the microsoft runtime +libraries, which by default is \f(CW64\fR (there must be a hidden \fI64\fR fetish +or something like this inside microsoft). You can increase this by calling +\&\f(CW\*(C`_setmaxstdio\*(C'\fR, which can increase this limit to \f(CW2048\fR (another +arbitrary limit), but is broken in many versions of the microsoft runtime +libraries. +.Sp +This might get you to about \f(CW512\fR or \f(CW2048\fR sockets (depending on +windows version and/or the phase of the moon). To get more, you need to +wrap all I/O functions and provide your own fd management, but the cost of +calling select (O(nA\*^X)) will likely make this unworkable. +.SH "PORTABILITY REQUIREMENTS" +.IX Header "PORTABILITY REQUIREMENTS" +In addition to a working ISO-C implementation, libev relies on a few +additional extensions: +.ie n .IP """sig_atomic_t volatile"" must be thread-atomic as well" 4 +.el .IP "\f(CWsig_atomic_t volatile\fR must be thread-atomic as well" 4 +.IX Item "sig_atomic_t volatile must be thread-atomic as well" +The type \f(CW\*(C`sig_atomic_t volatile\*(C'\fR (or whatever is defined as +\&\f(CW\*(C`EV_ATOMIC_T\*(C'\fR) must be atomic w.r.t. accesses from different +threads. This is not part of the specification for \f(CW\*(C`sig_atomic_t\*(C'\fR, but is +believed to be sufficiently portable. +.ie n .IP """sigprocmask"" must work in a threaded environment" 4 +.el .IP "\f(CWsigprocmask\fR must work in a threaded environment" 4 +.IX Item "sigprocmask must work in a threaded environment" +Libev uses \f(CW\*(C`sigprocmask\*(C'\fR to temporarily block signals. This is not +allowed in a threaded program (\f(CW\*(C`pthread_sigmask\*(C'\fR has to be used). Typical +pthread implementations will either allow \f(CW\*(C`sigprocmask\*(C'\fR in the \*(L"main +thread\*(R" or will block signals process-wide, both behaviours would +be compatible with libev. Interaction between \f(CW\*(C`sigprocmask\*(C'\fR and +\&\f(CW\*(C`pthread_sigmask\*(C'\fR could complicate things, however. +.Sp +The most portable way to handle signals is to block signals in all threads +except the initial one, and run the default loop in the initial thread as +well. +.ie n .IP """long"" must be large enough for common memory allocation sizes" 4 +.el .IP "\f(CWlong\fR must be large enough for common memory allocation sizes" 4 +.IX Item "long must be large enough for common memory allocation sizes" +To improve portability and simplify using libev, libev uses \f(CW\*(C`long\*(C'\fR +internally instead of \f(CW\*(C`size_t\*(C'\fR when allocating its data structures. On +non-POSIX systems (Microsoft...) this might be unexpectedly low, but +is still at least 31 bits everywhere, which is enough for hundreds of +millions of watchers. +.ie n .IP """double"" must hold a time value in seconds with enough accuracy" 4 +.el .IP "\f(CWdouble\fR must hold a time value in seconds with enough accuracy" 4 +.IX Item "double must hold a time value in seconds with enough accuracy" +The type \f(CW\*(C`double\*(C'\fR is used to represent timestamps. It is required to +have at least 51 bits of mantissa (and 9 bits of exponent), which is good +enough for at least into the year 4000. This requirement is fulfilled by +implementations implementing \s-1IEEE\s0 754 (basically all existing ones). +.PP +If you know of other additional requirements drop me a note. +.SH "AUTHOR" +.IX Header "AUTHOR" +Marc Lehmann <libev@schmorp.de>. +.SH "POD ERRORS" +.IX Header "POD ERRORS" +Hey! \fBThe above document had some coding errors, which are explained below:\fR +.IP "Around line 3052:" 4 +.IX Item "Around line 3052:" +You forgot a '=back' before '=head2' |