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| author | root <root> | 2007-11-12 07:58:13 +0000 |
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| committer | root <root> | 2007-11-12 07:58:13 +0000 |
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| parent | 80b007e04bb3f75ae92cf173ccb6af0510b214ba (diff) | |
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@@ -0,0 +1,719 @@ +<?xml version="1.0" encoding="UTF-8"?> +<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.1//EN" "http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd"> +<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en"> +<head> + <title>libev</title> + <meta name="description" content="Pod documentation for libev" /> + <meta name="inputfile" content="<standard input>" /> + <meta name="outputfile" content="<standard output>" /> + <meta name="created" content="Mon Nov 12 08:58:02 2007" /> + <meta name="generator" content="Pod::Xhtml 1.57" /> +<link rel="stylesheet" href="http://res.tst.eu/pod.css"/></head> +<body> +<div class="pod"> +<!-- INDEX START --> +<h3 id="TOP">Index</h3> + +<ul><li><a href="#NAME">NAME</a></li> +<li><a href="#SYNOPSIS">SYNOPSIS</a></li> +<li><a href="#DESCRIPTION">DESCRIPTION</a></li> +<li><a href="#FEATURES">FEATURES</a></li> +<li><a href="#CONVENTIONS">CONVENTIONS</a></li> +<li><a href="#TIME_AND_OTHER_GLOBAL_FUNCTIONS">TIME AND OTHER GLOBAL FUNCTIONS</a></li> +<li><a href="#FUNCTIONS_CONTROLLING_THE_EVENT_LOOP">FUNCTIONS CONTROLLING THE EVENT LOOP</a></li> +<li><a href="#ANATOMY_OF_A_WATCHER">ANATOMY OF A WATCHER</a> +<ul><li><a href="#ASSOCIATING_CUSTOM_DATA_WITH_A_WATCH">ASSOCIATING CUSTOM DATA WITH A WATCHER</a></li> +</ul> +</li> +<li><a href="#WATCHER_TYPES">WATCHER TYPES</a> +<ul><li><a href="#struct_ev_io_is_my_file_descriptor_r">struct ev_io - is my file descriptor readable or writable</a></li> +<li><a href="#struct_ev_timer_relative_and_optiona">struct ev_timer - relative and optionally recurring timeouts</a></li> +<li><a href="#ev_periodic">ev_periodic</a></li> +<li><a href="#ev_signal_signal_me_when_a_signal_ge">ev_signal - signal me when a signal gets signalled</a></li> +<li><a href="#ev_child_wait_for_pid_status_changes">ev_child - wait for pid status changes</a></li> +<li><a href="#ev_idle_when_you_ve_got_nothing_bett">ev_idle - when you've got nothing better to do</a></li> +<li><a href="#prepare_and_check_your_hooks_into_th">prepare and check - your hooks into the event loop</a></li> +</ul> +</li> +<li><a href="#OTHER_FUNCTIONS">OTHER FUNCTIONS</a></li> +<li><a href="#AUTHOR">AUTHOR</a> +</li> +</ul><hr /> +<!-- INDEX END --> + +<h1 id="NAME">NAME</h1><p><a href="#TOP" class="toplink">Top</a></p> +<div id="NAME_CONTENT"> +<p>libev - a high performance full-featured event loop written in C</p> + +</div> +<h1 id="SYNOPSIS">SYNOPSIS</h1><p><a href="#TOP" class="toplink">Top</a></p> +<div id="SYNOPSIS_CONTENT"> +<pre> #include <ev.h> + +</pre> + +</div> +<h1 id="DESCRIPTION">DESCRIPTION</h1><p><a href="#TOP" class="toplink">Top</a></p> +<div id="DESCRIPTION_CONTENT"> +<p>Libev is an event loop: you register interest in certain events (such as a +file descriptor being readable or a timeout occuring), and it will manage +these event sources and provide your program events.</p> +<p>To do this, it must take more or less complete control over your process +(or thread) by executing the <i>event loop</i> handler, and will then +communicate events via a callback mechanism.</p> +<p>You register interest in certain events by registering so-called <i>event +watchers</i>, which are relatively small C structures you initialise with the +details of the event, and then hand it over to libev by <i>starting</i> the +watcher.</p> + +</div> +<h1 id="FEATURES">FEATURES</h1><p><a href="#TOP" class="toplink">Top</a></p> +<div id="FEATURES_CONTENT"> +<p>Libev supports select, poll, the linux-specific epoll and the bsd-specific +kqueue mechanisms for file descriptor events, relative timers, absolute +timers with customised rescheduling, signal events, process status change +events (related to SIGCHLD), and event watchers dealing with the event +loop mechanism itself (idle, prepare and check watchers).</p> + +</div> +<h1 id="CONVENTIONS">CONVENTIONS</h1><p><a href="#TOP" class="toplink">Top</a></p> +<div id="CONVENTIONS_CONTENT"> +<p>Libev is very configurable. In this manual the default configuration +will be described, which supports multiple event loops. For more info +about various configuraiton options please have a look at the file +<cite>README.embed</cite> in the libev distribution. If libev was configured without +support for multiple event loops, then all functions taking an initial +argument of name <code>loop</code> (which is always of type <code>struct ev_loop *</code>) +will not have this argument.</p> + +</div> +<h1 id="TIME_AND_OTHER_GLOBAL_FUNCTIONS">TIME AND OTHER GLOBAL FUNCTIONS</h1><p><a href="#TOP" class="toplink">Top</a></p> +<div id="TIME_AND_OTHER_GLOBAL_FUNCTIONS_CONT"> +<p>Libev represents time as a single floating point number. This type is +called <code>ev_tstamp</code>, which is what you should use too. It usually aliases +to the double type in C.</p> +<dl> + <dt>ev_tstamp ev_time ()</dt> + <dd> + <p>Returns the current time as libev would use it.</p> + </dd> + <dt>int ev_version_major ()</dt> + <dt>int ev_version_minor ()</dt> + <dd> + <p>You can find out the major and minor version numbers of the library +you linked against by calling the functions <code>ev_version_major</code> and +<code>ev_version_minor</code>. If you want, you can compare against the global +symbols <code>EV_VERSION_MAJOR</code> and <code>EV_VERSION_MINOR</code>, which specify the +version of the library your program was compiled against.</p> + <p>Usually, its 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.</p> + </dd> + <dt>ev_set_allocator (void *(*cb)(void *ptr, long size))</dt> + <dd> + <p>Sets the allocation function to use (the prototype is similar to the +realloc function). It is used to allocate and free memory (no surprises +here). If it returns zero when memory needs to be allocated, the library +might abort or take some potentially destructive action. The default is +your system realloc function.</p> + <p>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.</p> + </dd> + <dt>ev_set_syserr_cb (void (*cb)(const char *msg));</dt> + <dd> + <p>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 geenrally retry the +requested operation, or, if the condition doesn't go away, do bad stuff +(such as abort).</p> + </dd> +</dl> + +</div> +<h1 id="FUNCTIONS_CONTROLLING_THE_EVENT_LOOP">FUNCTIONS CONTROLLING THE EVENT LOOP</h1><p><a href="#TOP" class="toplink">Top</a></p> +<div id="FUNCTIONS_CONTROLLING_THE_EVENT_LOOP-2"> +<p>An event loop is described by a <code>struct ev_loop *</code>. The library knows two +types of such loops, the <i>default</i> loop, which supports signals and child +events, and dynamically created loops which do not.</p> +<p>If you use threads, a common model is to run the default event loop +in your main thread (or in a separate thrad) and for each thread you +create, you also create another event loop. Libev itself does no lockign +whatsoever, so if you mix calls to different event loops, make sure you +lock (this is usually a bad idea, though, even if done right).</p> +<dl> + <dt>struct ev_loop *ev_default_loop (unsigned int flags)</dt> + <dd> + <p>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).</p> + <p>If you don't know what event loop to use, use the one returned from this +function.</p> + <p>The flags argument can be used to specify special behaviour or specific +backends to use, and is usually specified as 0 (or EVFLAG_AUTO)</p> + <p>It supports the following flags:</p> + <p> + <dl> + <dt>EVFLAG_AUTO</dt> + <dd> + <p>The default flags value. Use this if you have no clue (its the right +thing, believe me).</p> + </dd> + <dt>EVFLAG_NOENV</dt> + <dd> + <p>If this flag bit is ored into the flag value then libev will <i>not</i> look +at the environment variable <code>LIBEV_FLAGS</code>. Otherwise (the default), this +environment variable will override the flags completely. This is useful +to try out specific backends to tets their performance, or to work around +bugs.</p> + </dd> + <dt>EVMETHOD_SELECT portable select backend</dt> + <dt>EVMETHOD_POLL poll backend (everywhere except windows)</dt> + <dt>EVMETHOD_EPOLL linux only</dt> + <dt>EVMETHOD_KQUEUE some bsds only</dt> + <dt>EVMETHOD_DEVPOLL solaris 8 only</dt> + <dt>EVMETHOD_PORT solaris 10 only</dt> + <dd> + <p>If one or more of these are ored into the flags value, then only these +backends will be tried (in the reverse order as given here). If one are +specified, any backend will do.</p> + </dd> + </dl> + </p> + </dd> + <dt>struct ev_loop *ev_loop_new (unsigned int flags)</dt> + <dd> + <p>Similar to <code>ev_default_loop</code>, 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).</p> + </dd> + <dt>ev_default_destroy ()</dt> + <dd> + <p>Destroys the default loop again (frees all memory and kernel state +etc.). This stops all registered event watchers (by not touching them in +any way whatsoever, although you cnanot rely on this :).</p> + </dd> + <dt>ev_loop_destroy (loop)</dt> + <dd> + <p>Like <code>ev_default_destroy</code>, but destroys an event loop created by an +earlier call to <code>ev_loop_new</code>.</p> + </dd> + <dt>ev_default_fork ()</dt> + <dd> + <p>This function reinitialises the kernel state for backends that have +one. Despite the name, you can call it anytime, but it makes most sense +after forking, in either the parent or child process (or both, but that +again makes little sense).</p> + <p>You <i>must</i> call this function after forking if and only if you want to +use the event library in both processes. If you just fork+exec, you don't +have to call it.</p> + <p>The function itself is quite fast and its 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 <code>pthread_atfork</code>:</p> +<pre> pthread_atfork (0, 0, ev_default_fork); + +</pre> + </dd> + <dt>ev_loop_fork (loop)</dt> + <dd> + <p>Like <code>ev_default_fork</code>, but acts on an event loop created by +<code>ev_loop_new</code>. Yes, you have to call this on every allocated event loop +after fork, and how you do this is entirely your own problem.</p> + </dd> + <dt>unsigned int ev_method (loop)</dt> + <dd> + <p>Returns one of the <code>EVMETHOD_*</code> flags indicating the event backend in +use.</p> + </dd> + <dt>ev_tstamp = ev_now (loop)</dt> + <dd> + <p>Returns the current "event loop time", which is the time the event loop +got 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 +occuring (or more correctly, the mainloop finding out about it).</p> + </dd> + <dt>ev_loop (loop, int flags)</dt> + <dd> + <p>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.</p> + <p>If the flags argument is specified as 0, it will not return until either +no event watchers are active anymore or <code>ev_unloop</code> was called.</p> + <p>A flags value of <code>EVLOOP_NONBLOCK</code> 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.</p> + <p>A flags value of <code>EVLOOP_ONESHOT</code> 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.</p> + <p>This flags value could be used to implement alternative looping +constructs, but the <code>prepare</code> and <code>check</code> watchers provide a better and +more generic mechanism.</p> + </dd> + <dt>ev_unloop (loop, how)</dt> + <dd> + <p>Can be used to make a call to <code>ev_loop</code> return early. The <code>how</code> argument +must be either <code>EVUNLOOP_ONCE</code>, which will make the innermost <code>ev_loop</code> +call return, or <code>EVUNLOOP_ALL</code>, which will make all nested <code>ev_loop</code> +calls return.</p> + </dd> + <dt>ev_ref (loop)</dt> + <dt>ev_unref (loop)</dt> + <dd> + <p>Ref/unref can be used to add or remove a refcount on the event loop: Every +watcher keeps one reference. If you have a long-runing watcher you never +unregister that should not keep ev_loop from running, ev_unref() after +starting, and ev_ref() before stopping it. Libev itself uses this for +example for its internal signal pipe: It is not visible to you as a user +and should not keep <code>ev_loop</code> from exiting if the work is done. It is +also an excellent way to do this for generic recurring timers or from +within third-party libraries. Just remember to unref after start and ref +before stop.</p> + </dd> +</dl> + +</div> +<h1 id="ANATOMY_OF_A_WATCHER">ANATOMY OF A WATCHER</h1><p><a href="#TOP" class="toplink">Top</a></p> +<div id="ANATOMY_OF_A_WATCHER_CONTENT"> +<p>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 STDIN to +become readable, you would create an ev_io watcher for that:</p> +<pre> 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); + +</pre> +<p>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).</p> +<p>Each watcher structure must be initialised by a call to <code>ev_init +(watcher *, callback)</code>, 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).</p> +<p>Each watcher type has its own <code>ev_<type>_set (watcher *, ...)</code> macro +with arguments specific to this watcher type. There is also a macro +to combine initialisation and setting in one call: <code>ev_<type>_init +(watcher *, callback, ...)</code>.</p> +<p>To make the watcher actually watch out for events, you have to start it +with a watcher-specific start function (<code>ev_<type>_start (loop, watcher +*)</code>), and you can stop watching for events at any time by calling the +corresponding stop function (<code>ev_<type>_stop (loop, watcher *)</code>.</p> +<p>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 set method.</p> +<p>You cna check wether an event is active by calling the <code>ev_is_active +(watcher *)</code> macro. To see wether an event is outstanding (but the +callback for it has not been called yet) you cna use the <code>ev_is_pending +(watcher *)</code> macro.</p> +<p>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.</p> +<p>The rceeived events usually include a single bit per event type received +(you can receive multiple events at the same time). The possible bit masks +are:</p> +<dl> + <dt>EV_READ</dt> + <dt>EV_WRITE</dt> + <dd> + <p>The file descriptor in the ev_io watcher has become readable and/or +writable.</p> + </dd> + <dt>EV_TIMEOUT</dt> + <dd> + <p>The ev_timer watcher has timed out.</p> + </dd> + <dt>EV_PERIODIC</dt> + <dd> + <p>The ev_periodic watcher has timed out.</p> + </dd> + <dt>EV_SIGNAL</dt> + <dd> + <p>The signal specified in the ev_signal watcher has been received by a thread.</p> + </dd> + <dt>EV_CHILD</dt> + <dd> + <p>The pid specified in the ev_child watcher has received a status change.</p> + </dd> + <dt>EV_IDLE</dt> + <dd> + <p>The ev_idle watcher has determined that you have nothing better to do.</p> + </dd> + <dt>EV_PREPARE</dt> + <dt>EV_CHECK</dt> + <dd> + <p>All ev_prepare watchers are invoked just <i>before</i> <code>ev_loop</code> starts +to gather new events, and all ev_check watchers are invoked just after +<code>ev_loop</code> 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 ev_prepare watcher might start an idle watcher to keep +<code>ev_loop</code> from blocking).</p> + </dd> + <dt>EV_ERROR</dt> + <dd> + <p>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.</p> + <p>Libev will usually signal a few "dummy" 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 read() or write(). This will not work in multithreaded +programs, though, so beware.</p> + </dd> +</dl> + +</div> +<h2 id="ASSOCIATING_CUSTOM_DATA_WITH_A_WATCH">ASSOCIATING CUSTOM DATA WITH A WATCHER</h2> +<div id="ASSOCIATING_CUSTOM_DATA_WITH_A_WATCH-2"> +<p>Each watcher has, by default, a member <code>void *data</code> that you can change +and read at any time, libev will completely ignore it. This cna 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 "subclass" the watcher type and provide your own +data:</p> +<pre> struct my_io + { + struct ev_io io; + int otherfd; + void *somedata; + struct whatever *mostinteresting; + } + +</pre> +<p>And since your callback will be called with a pointer to the watcher, you +can cast it back to your own type:</p> +<pre> static void my_cb (struct ev_loop *loop, struct ev_io *w_, int revents) + { + struct my_io *w = (struct my_io *)w_; + ... + } + +</pre> +<p>More interesting and less C-conformant ways of catsing your callback type +have been omitted....</p> + + + + + +</div> +<h1 id="WATCHER_TYPES">WATCHER TYPES</h1><p><a href="#TOP" class="toplink">Top</a></p> +<div id="WATCHER_TYPES_CONTENT"> +<p>This section describes each watcher in detail, but will not repeat +information given in the last section.</p> + +</div> +<h2 id="struct_ev_io_is_my_file_descriptor_r">struct ev_io - is my file descriptor readable or writable</h2> +<div id="struct_ev_io_is_my_file_descriptor_r-2"> +<p>I/O watchers check wether a file descriptor is readable or writable +in each iteration of the event loop (This behaviour is called +level-triggering because you keep receiving events as long as the +condition persists. Remember you cna stop the watcher if you don't want to +act on the event and neither want to receive future events).</p> +<dl> + <dt>ev_io_init (ev_io *, callback, int fd, int events)</dt> + <dt>ev_io_set (ev_io *, int fd, int events)</dt> + <dd> + <p>Configures an ev_io watcher. The fd is the file descriptor to rceeive +events for and events is either <code>EV_READ</code>, <code>EV_WRITE</code> or <code>EV_READ | +EV_WRITE</code> to receive the given events.</p> + </dd> +</dl> + +</div> +<h2 id="struct_ev_timer_relative_and_optiona">struct ev_timer - relative and optionally recurring timeouts</h2> +<div id="struct_ev_timer_relative_and_optiona-2"> +<p>Timer watchers are simple relative timers that generate an event after a +given time, and optionally repeating in regular intervals after that.</p> +<p>The timers are based on real time, that is, if you register an event that +times out after an hour and youreset your system clock to last years +time, it will still time out after (roughly) and hour. "Roughly" because +detecting time jumps is hard, and soem inaccuracies are unavoidable (the +monotonic clock option helps a lot here).</p> +<dl> + <dt>ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)</dt> + <dt>ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)</dt> + <dd> + <p>Configure the timer to trigger after <code>after</code> seconds. If <code>repeat</code> is +<code>0.</code>, then it will automatically be stopped. If it is positive, then the +timer will automatically be configured to trigger again <code>repeat</code> seconds +later, again, and again, until stopped manually.</p> + <p>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 (ecause it takes longer than those 10 seconds to do stuff) the +timer will not fire more than once per event loop iteration.</p> + </dd> + <dt>ev_timer_again (loop)</dt> + <dd> + <p>This will act as if the timer timed out and restart it again if it is +repeating. The exact semantics are:</p> + <p>If the timer is started but nonrepeating, stop it.</p> + <p>If the timer is repeating, either start it if necessary (with the repeat +value), or reset the running timer to the repeat value.</p> + <p>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 ev_timer with after=repeat=60 and calling ev_timer_again 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 stop +the timer, and again will automatically restart it if need be.</p> + </dd> +</dl> + +</div> +<h2 id="ev_periodic">ev_periodic</h2> +<div id="ev_periodic_CONTENT"> +<p>Periodic watchers are also timers of a kind, but they are very versatile +(and unfortunately a bit complex).</p> +<p>Unlike ev_timer'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 "at" some specific point in time. For example, if you tell a +periodic watcher to trigger in 10 seconds (by specifiying e.g. c<ev_now () ++ 10.>) and then reset your system clock to the last year, then it will +take a year to trigger the event (unlike an ev_timer, which would trigger +roughly 10 seconds later and of course not if you reset your system time +again).</p> +<p>They can also be used to implement vastly more complex timers, such as +triggering an event on eahc midnight, local time.</p> +<dl> + <dt>ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)</dt> + <dt>ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)</dt> + <dd> + <p>Lots of arguments, lets sort it out... There are basically three modes of +operation, and we will explain them from simplest to complex:</p> + + + + + <p> + <dl> + <dt>* absolute timer (interval = reschedule_cb = 0)</dt> + <dd> + <p>In this configuration the watcher triggers an event at the wallclock time +<code>at</code> 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.</p> + </dd> + <dt>* non-repeating interval timer (interval > 0, reschedule_cb = 0)</dt> + <dd> + <p>In this mode the watcher will always be scheduled to time out at the next +<code>at + N * interval</code> time (for some integer N) and then repeat, regardless +of any time jumps.</p> + <p>This can be used to create timers that do not drift with respect to system +time:</p> +<pre> ev_periodic_set (&periodic, 0., 3600., 0); + +</pre> + <p>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 (UTC), or more correct, when the system time is evenly divisible +by 3600.</p> + <p>Another way to think about it (for the mathematically inclined) is that +ev_periodic will try to run the callback in this mode at the next possible +time where <code>time = at (mod interval)</code>, regardless of any time jumps.</p> + </dd> + <dt>* manual reschedule mode (reschedule_cb = callback)</dt> + <dd> + <p>In this mode the values for <code>interval</code> and <code>at</code> 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.</p> + <p>NOTE: <i>This callback MUST NOT stop or destroy the periodic or any other +periodic watcher, ever, or make any event loop modificstions</i>. If you need +to stop it, return 1e30 (or so, fudge fudge) and stop it afterwards.</p> + <p>Its prototype is c<ev_tstamp (*reschedule_cb)(struct ev_periodic *w, +ev_tstamp now)>, e.g.:</p> +<pre> static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now) + { + return now + 60.; + } + +</pre> + <p>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.</p> + <p>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 <code>now</code> and return the timestamp value for this. How you do this +is, again, up to you (but it is not trivial).</p> + </dd> + </dl> + </p> + </dd> + <dt>ev_periodic_again (loop, ev_periodic *)</dt> + <dd> + <p>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).</p> + </dd> +</dl> + +</div> +<h2 id="ev_signal_signal_me_when_a_signal_ge">ev_signal - signal me when a signal gets signalled</h2> +<div id="ev_signal_signal_me_when_a_signal_ge-2"> +<p>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 its best to deliver signals synchronously, i.e. as part of the +normal event processing, like any other event.</p> +<p>You cna 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 +SIG_DFL (regardless of what it was set to before).</p> +<dl> + <dt>ev_signal_init (ev_signal *, callback, int signum)</dt> + <dt>ev_signal_set (ev_signal *, int signum)</dt> + <dd> + <p>Configures the watcher to trigger on the given signal number (usually one +of the <code>SIGxxx</code> constants).</p> + </dd> +</dl> + +</div> +<h2 id="ev_child_wait_for_pid_status_changes">ev_child - wait for pid status changes</h2> +<div id="ev_child_wait_for_pid_status_changes-2"> +<p>Child watchers trigger when your process receives a SIGCHLD in response to +some child status changes (most typically when a child of yours dies).</p> +<dl> + <dt>ev_child_init (ev_child *, callback, int pid)</dt> + <dt>ev_child_set (ev_child *, int pid)</dt> + <dd> + <p>Configures the watcher to wait for status changes of process <code>pid</code> (or +<i>any</i> process if <code>pid</code> is specified as <code>0</code>). The callback can look +at the <code>rstatus</code> member of the <code>ev_child</code> watcher structure to see +the status word (use the macros from <code>sys/wait.h</code>). The <code>rpid</code> member +contains the pid of the process causing the status change.</p> + </dd> +</dl> + +</div> +<h2 id="ev_idle_when_you_ve_got_nothing_bett">ev_idle - when you've got nothing better to do</h2> +<div id="ev_idle_when_you_ve_got_nothing_bett-2"> +<p>Idle watchers trigger events when there are no other I/O or timer (or +periodic) events pending. That is, as long as your process is busy +handling sockets or timeouts it will not be called. But when your process +is idle all idle watchers are being called again and again - until +stopped, that is, or your process receives more events.</p> +<p>The most noteworthy effect is that as long as any idle watchers are +active, the process will not block when waiting for new events.</p> +<p>Apart from keeping your process non-blocking (which is a useful +effect on its own sometimes), idle watchers are a good place to do +"pseudo-background processing", or delay processing stuff to after the +event loop has handled all outstanding events.</p> +<dl> + <dt>ev_idle_init (ev_signal *, callback)</dt> + <dd> + <p>Initialises and configures the idle watcher - it has no parameters of any +kind. There is a <code>ev_idle_set</code> macro, but using it is utterly pointless, +believe me.</p> + </dd> +</dl> + +</div> +<h2 id="prepare_and_check_your_hooks_into_th">prepare and check - your hooks into the event loop</h2> +<div id="prepare_and_check_your_hooks_into_th-2"> +<p>Prepare and check watchers usually (but not always) are used in +tandom. Prepare watchers get invoked before the process blocks and check +watchers afterwards.</p> +<p>Their main purpose is to integrate other event mechanisms into libev. This +could be used, for example, to track variable changes, implement your own +watchers, integrate net-snmp or a coroutine library and lots more.</p> +<p>This is done by examining in each prepare call which file descriptors need +to be watched by the other library, registering ev_io watchers for them +and starting an ev_timer watcher for any timeouts (many libraries provide +just this functionality). Then, in the check watcher you check for any +events that occured (by making your callbacks set soem flags for example) +and call back into the library.</p> +<p>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.</p> +<dl> + <dt>ev_prepare_init (ev_prepare *, callback)</dt> + <dt>ev_check_init (ev_check *, callback)</dt> + <dd> + <p>Initialises and configures the prepare or check watcher - they have no +parameters of any kind. There are <code>ev_prepare_set</code> and <code>ev_check_set</code> +macros, but using them is utterly, utterly pointless.</p> + </dd> +</dl> + +</div> +<h1 id="OTHER_FUNCTIONS">OTHER FUNCTIONS</h1><p><a href="#TOP" class="toplink">Top</a></p> +<div id="OTHER_FUNCTIONS_CONTENT"> +<p>There are some other fucntions of possible interest. Described. Here. Now.</p> +<dl> + <dt>ev_once (loop, int fd, int events, ev_tstamp timeout, callback)</dt> + <dd> + <p>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 havign to allocate/configure/start/stop/free one or +more watchers yourself.</p> + <p>If <code>fd</code> is less than 0, then no I/O watcher will be started and events is +ignored. Otherwise, an ev_io watcher for the given <code>fd</code> and <code>events</code> set +will be craeted and started.</p> + <p>If <code>timeout</code> is less than 0, then no timeout watcher will be +started. Otherwise an ev_timer watcher with after = <code>timeout</code> (and repeat += 0) will be started.</p> + <p>The callback has the type <code>void (*cb)(int revents, void *arg)</code> and +gets passed an events set (normally a combination of EV_ERROR, EV_READ, +EV_WRITE or EV_TIMEOUT) and the <code>arg</code> value passed to <code>ev_once</code>:</p> +<pre> 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_READm 10., stdin_ready, 0); + +</pre> + </dd> + <dt>ev_feed_event (loop, watcher, int events)</dt> + <dd> + <p>Feeds the given event set into the event loop, as if the specified event +has happened for the specified watcher (which must be a pointer to an +initialised but not necessarily active event watcher).</p> + </dd> + <dt>ev_feed_fd_event (loop, int fd, int revents)</dt> + <dd> + <p>Feed an event on the given fd, as if a file descriptor backend detected it.</p> + </dd> + <dt>ev_feed_signal_event (loop, int signum)</dt> + <dd> + <p>Feed an event as if the given signal occured (loop must be the default loop!).</p> + </dd> +</dl> + +</div> +<h1 id="AUTHOR">AUTHOR</h1><p><a href="#TOP" class="toplink">Top</a></p> +<div id="AUTHOR_CONTENT"> +<p>Marc Lehmann <libev@schmorp.de>.</p> + +</div> +</div></body> +</html> |