diff options
| -rw-r--r-- | ev.pod | 239 |
1 files changed, 170 insertions, 69 deletions
@@ -19,7 +19,7 @@ libev - a high performance full-featured event loop written in C // 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) + stdin_cb (EV_P_ ev_io *w, int revents) { puts ("stdin ready"); // for one-shot events, one must manually stop the watcher @@ -32,7 +32,7 @@ libev - a high performance full-featured event loop written in C // another callback, this time for a time-out static void - timeout_cb (EV_P_ struct ev_timer *w, int revents) + timeout_cb (EV_P_ ev_timer *w, int revents) { puts ("timeout"); // this causes the innermost ev_loop to stop iterating @@ -43,7 +43,7 @@ libev - a high performance full-featured event loop written in C main (void) { // use the default event loop unless you have special needs - struct ev_loop *loop = ev_default_loop (0); + ev_loop *loop = ev_default_loop (0); // initialise an io watcher, then start it // this one will watch for stdin to become readable @@ -105,7 +105,7 @@ configuration will be described, which supports multiple event loops. For more info about various configuration options please have a look at B<EMBED> section in this manual. If libev was configured without support for multiple event loops, then all functions taking an initial argument of -name C<loop> (which is always of type C<struct ev_loop *>) will not have +name C<loop> (which is always of type C<ev_loop *>) will not have this argument. =head2 TIME REPRESENTATION @@ -278,7 +278,7 @@ Example: This is basically the same thing that libev does internally, too. =head1 FUNCTIONS CONTROLLING THE EVENT LOOP -An event loop is described by a C<struct ev_loop *>. The library knows two +An event loop is described by a C<ev_loop *>. The library knows two types of such loops, the I<default> loop, which supports signals and child events, and dynamically created loops which do not. @@ -712,7 +712,7 @@ respectively). Example: Create a signal watcher, but keep it from keeping C<ev_loop> running when nothing else is active. - struct ev_signal exitsig; + ev_signal exitsig; ev_signal_init (&exitsig, sig_cb, SIGINT); ev_signal_start (loop, &exitsig); evf_unref (loop); @@ -788,14 +788,14 @@ 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 C<ev_io> watcher for that: - static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents) + static void my_cb (struct ev_loop *loop, 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_io stdin_watcher; ev_init (&stdin_watcher, my_cb); ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ); ev_io_start (loop, &stdin_watcher); @@ -931,7 +931,7 @@ which rolls both calls into one. 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. -The callback is always of type C<void (*)(ev_loop *loop, ev_TYPE *watcher, +The callback is always of type C<void (*)(struct ev_loop *loop, ev_TYPE *watcher, int revents)>. Example: Initialise an C<ev_io> watcher in two steps. @@ -1066,7 +1066,7 @@ data: struct my_io { - struct ev_io io; + ev_io io; int otherfd; void *somedata; struct whatever *mostinteresting; @@ -1079,7 +1079,7 @@ data: And since your callback will be called with a pointer to the watcher, you can cast it back to your own type: - static void my_cb (struct ev_loop *loop, struct ev_io *w_, int revents) + static void my_cb (struct ev_loop *loop, ev_io *w_, int revents) { struct my_io *w = (struct my_io *)w_; ... @@ -1107,14 +1107,14 @@ programmers): #include <stddef.h> static void - t1_cb (EV_P_ struct ev_timer *w, int revents) + t1_cb (EV_P_ 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) + t2_cb (EV_P_ ev_timer *w, int revents) { struct my_biggy big = (struct my_biggy * (((char *)w) - offsetof (struct my_biggy, t2)); @@ -1259,7 +1259,7 @@ readable, but only once. Since it is likely line-buffered, you could attempt to read a whole line in the callback. static void - stdin_readable_cb (struct ev_loop *loop, struct ev_io *w, int revents) + stdin_readable_cb (struct ev_loop *loop, ev_io *w, int revents) { ev_io_stop (loop, w); .. read from stdin here (or from w->fd) and handle any I/O errors @@ -1267,7 +1267,7 @@ attempt to read a whole line in the callback. ... struct ev_loop *loop = ev_default_init (0); - struct ev_io stdin_readable; + 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); @@ -1288,6 +1288,134 @@ The callback is guaranteed to be invoked only I<after> its timeout has passed, but if multiple timers become ready during the same loop iteration then order of execution is undefined. +=head3 Be smart about timeouts + +Many real-world problems invole some kind of time-out, usually for error +recovery. A typical example is an HTTP request - if the other side hangs, +you want to raise some error after a while. + +Here are some ways on how to handle this problem, from simple and +inefficient to very efficient. + +In the following examples a 60 second activity timeout is assumed - a +timeout that gets reset to 60 seconds each time some data ("a lifesign") +was received. + +=over 4 + +=item 1. Use a timer and stop, reinitialise, start it on activity. + +This is the most obvious, but not the most simple way: In the beginning, +start the watcher: + + ev_timer_init (timer, callback, 60., 0.); + ev_timer_start (loop, timer); + +Then, each time there is some activity, C<ev_timer_stop> the timer, +initialise it again, and start it: + + ev_timer_stop (loop, timer); + ev_timer_set (timer, 60., 0.); + ev_timer_start (loop, timer); + +This is relatively simple to implement, but means that each time there +is some activity, libev will first have to remove the timer from it's +internal data strcuture and then add it again. + +=item 2. Use a timer and re-start it with C<ev_timer_again> inactivity. + +This is the easiest way, and involves using C<ev_timer_again> instead of +C<ev_timer_start>. + +For this, configure an C<ev_timer> with a C<repeat> value of C<60> and +then call C<ev_timer_again> at start and 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 C<ev_timer_stop> the timer, and +C<ev_timer_again> will automatically restart it if need be. + +That means you can ignore the C<after> value and C<ev_timer_start> +altogether and only ever use the C<repeat> value and C<ev_timer_again>. + +At start: + + ev_timer_init (timer, callback, 0., 60.); + ev_timer_again (loop, timer); + +Each time you receive some data: + + ev_timer_again (loop, timer); + +It is even possible to change the time-out on the fly: + + timer->repeat = 30.; + ev_timer_again (loop, timer); + +This is slightly more efficient then stopping/starting the timer each time +you want to modify its timeout value, as libev does not have to completely +remove and re-insert the timer from/into it's internal data structure. + +=item 3. Let the timer time out, but then re-arm it as required. + +This method is more tricky, but usually most efficient: Most timeouts are +relatively long compared to the loop iteration time - in our example, +within 60 seconds, there are usually many I/O events with associated +activity resets. + +In this case, it would be more efficient to leave the C<ev_timer> alone, +but remember the time of last activity, and check for a real timeout only +within the callback: + + ev_tstamp last_activity; // time of last activity + + static void + callback (EV_P_ ev_timer *w, int revents) + { + ev_tstamp now = ev_now (EV_A); + ev_tstamp timeout = last_activity + 60.; + + // if last_activity is older than now - timeout, we did time out + if (timeout < now) + { + // timeout occured, take action + } + else + { + // callback was invoked, but there was some activity, re-arm + // to fire in last_activity + 60. + w->again = timeout - now; + ev_timer_again (EV_A_ w); + } + } + +To summarise the callback: first calculate the real time-out (defined as +"60 seconds after the last activity"), then check if that time has been +reached, which means there was a real timeout. Otherwise the callback was +invoked too early (timeout is in the future), so re-schedule the timer to +fire at that future time. + +Note how C<ev_timer_again> is used, taking advantage of the +C<ev_timer_again> optimisation when the timer is already running. + +This scheme causes more callback invocations (about one every 60 seconds), +but virtually no calls to libev to change the timeout. + +To start the timer, simply intiialise the watcher and C<last_activity>, +then call the callback: + + ev_timer_init (timer, callback); + last_activity = ev_now (loop); + callback (loop, timer, EV_TIMEOUT); + +And when there is some activity, simply remember the time in +C<last_activity>: + + last_actiivty = ev_now (loop); + +This technique is slightly more complex, but in most cases where the +time-out is unlikely to be triggered, much more efficient. + +=back + =head3 The special problem of time updates Establishing the current time is a costly operation (it usually takes at @@ -1340,36 +1468,8 @@ If the timer is started but non-repeating, stop it (as if it timed out). If the timer is repeating, either start it if necessary (with the C<repeat> value), or reset the running timer to the C<repeat> value. -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 C<ev_timer> with a C<repeat> value of C<60> and then call -C<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 C<ev_timer_stop> the timer, and C<ev_timer_again> will -automatically restart it if need be. - -That means you can ignore the C<after> value and C<ev_timer_start> -altogether and only ever use the C<repeat> value and C<ev_timer_again>: - - 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); - -This is more slightly efficient then stopping/starting the timer each time -you want to modify its timeout value. - -Note, however, that it is often even more efficient to remember the -time of the last activity and let the timer time-out naturally. In the -callback, you then check whether the time-out is real, or, if there was -some activity, you reschedule the watcher to time-out in "last_activity + -timeout - ev_now ()" seconds. +This sounds a bit complicated, see "Be smart about timeouts", above, for a +usage example. =item ev_tstamp repeat [read-write] @@ -1384,12 +1484,12 @@ which is also when any modifications are taken into account. Example: Create a timer that fires after 60 seconds. static void - one_minute_cb (struct ev_loop *loop, struct ev_timer *w, int revents) + one_minute_cb (struct ev_loop *loop, ev_timer *w, int revents) { .. one minute over, w is actually stopped right here } - struct ev_timer mytimer; + ev_timer mytimer; ev_timer_init (&mytimer, one_minute_cb, 60., 0.); ev_timer_start (loop, &mytimer); @@ -1397,12 +1497,12 @@ Example: Create a timeout timer that times out after 10 seconds of inactivity. static void - timeout_cb (struct ev_loop *loop, struct ev_timer *w, int revents) + timeout_cb (struct ev_loop *loop, ev_timer *w, int revents) { .. ten seconds without any activity } - struct ev_timer mytimer; + 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); @@ -1498,10 +1598,11 @@ If you need to stop it, return C<now + 1e30> (or so, fudge fudge) and stop it afterwards (e.g. by starting an C<ev_prepare> watcher, which is the only event loop modification you are allowed to do). -The callback prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic +The callback prototype is C<ev_tstamp (*reschedule_cb)(ev_periodic *w, ev_tstamp now)>, e.g.: - static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now) + static ev_tstamp + my_rescheduler (ev_periodic *w, ev_tstamp now) { return now + 60.; } @@ -1548,7 +1649,7 @@ The current interval value. Can be modified any time, but changes only take effect when the periodic timer fires or C<ev_periodic_again> is being called. -=item ev_tstamp (*reschedule_cb)(struct ev_periodic *w, ev_tstamp now) [read-write] +=item ev_tstamp (*reschedule_cb)(ev_periodic *w, ev_tstamp now) [read-write] The current reschedule callback, or C<0>, if this functionality is switched off. Can be changed any time, but changes only take effect when @@ -1563,12 +1664,12 @@ system time is divisible by 3600. The callback invocation times have potentially a lot of jitter, but good long-term stability. static void - clock_cb (struct ev_loop *loop, struct ev_io *w, int revents) + clock_cb (struct ev_loop *loop, 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 hourly_tick; ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0); ev_periodic_start (loop, &hourly_tick); @@ -1577,7 +1678,7 @@ Example: The same as above, but use a reschedule callback to do it: #include <math.h> static ev_tstamp - my_scheduler_cb (struct ev_periodic *w, ev_tstamp now) + my_scheduler_cb (ev_periodic *w, ev_tstamp now) { return now + (3600. - fmod (now, 3600.)); } @@ -1586,7 +1687,7 @@ Example: The same as above, but use a reschedule callback to do it: Example: Call a callback every hour, starting now: - struct ev_periodic hourly_tick; + ev_periodic hourly_tick; ev_periodic_init (&hourly_tick, clock_cb, fmod (ev_now (loop), 3600.), 3600., 0); ev_periodic_start (loop, &hourly_tick); @@ -1638,12 +1739,12 @@ The signal the watcher watches out for. Example: Try to exit cleanly on SIGINT. static void - sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents) + sigint_cb (struct ev_loop *loop, ev_signal *w, int revents) { ev_unloop (loop, EVUNLOOP_ALL); } - struct ev_signal signal_watcher; + ev_signal signal_watcher; ev_signal_init (&signal_watcher, sigint_cb, SIGINT); ev_signal_start (loop, &signal_watcher); @@ -1728,7 +1829,7 @@ its completion. ev_child cw; static void - child_cb (EV_P_ struct ev_child *w, int revents) + child_cb (EV_P_ ev_child *w, int revents) { ev_child_stop (EV_A_ w); printf ("process %d exited with status %x\n", w->rpid, w->rstatus); @@ -1990,14 +2091,14 @@ Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the callback, free it. Also, use no error checking, as usual. static void - idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents) + idle_cb (struct ev_loop *loop, 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 *idle_watcher = malloc (sizeof (ev_idle)); ev_idle_init (idle_watcher, idle_cb); ev_idle_start (loop, idle_cb); @@ -2088,13 +2189,13 @@ the callbacks for the IO/timeout watchers might not have been called yet. static ev_timer tw; static void - io_cb (ev_loop *loop, ev_io *w, int revents) + io_cb (struct 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) + adns_prepare_cb (struct ev_loop *loop, ev_prepare *w, int revents) { int timeout = 3600000; struct pollfd fds [nfd]; @@ -2119,7 +2220,7 @@ the callbacks for the IO/timeout watchers might not have been called yet. // stop all watchers after blocking static void - adns_check_cb (ev_loop *loop, ev_check *w, int revents) + adns_check_cb (struct ev_loop *loop, ev_check *w, int revents) { ev_timer_stop (loop, &tw); @@ -2297,7 +2398,7 @@ used). struct ev_loop *loop_hi = ev_default_init (0); struct ev_loop *loop_lo = 0; - struct ev_embed embed; + ev_embed embed; // see if there is a chance of getting one that works // (remember that a flags value of 0 means autodetection) @@ -2321,7 +2422,7 @@ C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too). struct ev_loop *loop = ev_default_init (0); struct ev_loop *loop_socket = 0; - struct ev_embed embed; + ev_embed embed; if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE) if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE)) @@ -2545,18 +2646,18 @@ Example: wait up to ten seconds for data to appear on STDIN_FILENO. ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0); -=item ev_feed_event (ev_loop *, watcher *, int revents) +=item ev_feed_event (struct 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). -=item ev_feed_fd_event (ev_loop *, int fd, int revents) +=item ev_feed_fd_event (struct ev_loop *, int fd, int revents) Feed an event on the given fd, as if a file descriptor backend detected the given events it. -=item ev_feed_signal_event (ev_loop *loop, int signum) +=item ev_feed_signal_event (struct ev_loop *loop, int signum) Feed an event as if the given signal occurred (C<loop> must be the default loop!). |