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15 <h3 id="TOP">Index</h3>
17 <ul><li><a href="#NAME">NAME</a></li>
18 <li><a href="#SYNOPSIS">SYNOPSIS</a></li>
19 <li><a href="#DESCRIPTION">DESCRIPTION</a></li>
20 <li><a href="#FEATURES">FEATURES</a></li>
21 <li><a href="#CONVENTIONS">CONVENTIONS</a></li>
22 <li><a href="#TIME_AND_OTHER_GLOBAL_FUNCTIONS">TIME AND OTHER GLOBAL FUNCTIONS</a></li>
23 <li><a href="#FUNCTIONS_CONTROLLING_THE_EVENT_LOOP">FUNCTIONS CONTROLLING THE EVENT LOOP</a></li>
24 <li><a href="#ANATOMY_OF_A_WATCHER">ANATOMY OF A WATCHER</a>
25 <ul><li><a href="#ASSOCIATING_CUSTOM_DATA_WITH_A_WATCH">ASSOCIATING CUSTOM DATA WITH A WATCHER</a></li>
28 <li><a href="#WATCHER_TYPES">WATCHER TYPES</a>
29 <ul><li><a href="#struct_ev_io_is_my_file_descriptor_r">struct ev_io - is my file descriptor readable or writable</a></li>
30 <li><a href="#struct_ev_timer_relative_and_optiona">struct ev_timer - relative and optionally recurring timeouts</a></li>
31 <li><a href="#ev_periodic">ev_periodic</a></li>
32 <li><a href="#ev_signal_signal_me_when_a_signal_ge">ev_signal - signal me when a signal gets signalled</a></li>
33 <li><a href="#ev_child_wait_for_pid_status_changes">ev_child - wait for pid status changes</a></li>
34 <li><a href="#ev_idle_when_you_ve_got_nothing_bett">ev_idle - when you've got nothing better to do</a></li>
35 <li><a href="#prepare_and_check_your_hooks_into_th">prepare and check - your hooks into the event loop</a></li>
38 <li><a href="#OTHER_FUNCTIONS">OTHER FUNCTIONS</a></li>
39 <li><a href="#AUTHOR">AUTHOR</a>
44 <h1 id="NAME">NAME</h1><p><a href="#TOP" class="toplink">Top</a></p>
45 <div id="NAME_CONTENT">
46 <p>libev - a high performance full-featured event loop written in C</p>
49 <h1 id="SYNOPSIS">SYNOPSIS</h1><p><a href="#TOP" class="toplink">Top</a></p>
50 <div id="SYNOPSIS_CONTENT">
51 <pre> #include <ev.h>
56 <h1 id="DESCRIPTION">DESCRIPTION</h1><p><a href="#TOP" class="toplink">Top</a></p>
57 <div id="DESCRIPTION_CONTENT">
58 <p>Libev is an event loop: you register interest in certain events (such as a
59 file descriptor being readable or a timeout occuring), and it will manage
60 these event sources and provide your program events.</p>
61 <p>To do this, it must take more or less complete control over your process
62 (or thread) by executing the <i>event loop</i> handler, and will then
63 communicate events via a callback mechanism.</p>
64 <p>You register interest in certain events by registering so-called <i>event
65 watchers</i>, which are relatively small C structures you initialise with the
66 details of the event, and then hand it over to libev by <i>starting</i> the
70 <h1 id="FEATURES">FEATURES</h1><p><a href="#TOP" class="toplink">Top</a></p>
71 <div id="FEATURES_CONTENT">
72 <p>Libev supports select, poll, the linux-specific epoll and the bsd-specific
73 kqueue mechanisms for file descriptor events, relative timers, absolute
74 timers with customised rescheduling, signal events, process status change
75 events (related to SIGCHLD), and event watchers dealing with the event
76 loop mechanism itself (idle, prepare and check watchers).</p>
79 <h1 id="CONVENTIONS">CONVENTIONS</h1><p><a href="#TOP" class="toplink">Top</a></p>
80 <div id="CONVENTIONS_CONTENT">
81 <p>Libev is very configurable. In this manual the default configuration
82 will be described, which supports multiple event loops. For more info
83 about various configuraiton options please have a look at the file
84 <cite>README.embed</cite> in the libev distribution. If libev was configured without
85 support for multiple event loops, then all functions taking an initial
86 argument of name <code>loop</code> (which is always of type <code>struct ev_loop *</code>)
87 will not have this argument.</p>
90 <h1 id="TIME_AND_OTHER_GLOBAL_FUNCTIONS">TIME AND OTHER GLOBAL FUNCTIONS</h1><p><a href="#TOP" class="toplink">Top</a></p>
91 <div id="TIME_AND_OTHER_GLOBAL_FUNCTIONS_CONT">
92 <p>Libev represents time as a single floating point number, representing the
93 (fractional) number of seconds since the (POSIX) epoch (somewhere near
94 the beginning of 1970, details are complicated, don't ask). This type is
95 called <code>ev_tstamp</code>, which is what you should use too. It usually aliases
96 to the double type in C.</p>
98 <dt>ev_tstamp ev_time ()</dt>
100 <p>Returns the current time as libev would use it.</p>
102 <dt>int ev_version_major ()</dt>
103 <dt>int ev_version_minor ()</dt>
105 <p>You can find out the major and minor version numbers of the library
106 you linked against by calling the functions <code>ev_version_major</code> and
107 <code>ev_version_minor</code>. If you want, you can compare against the global
108 symbols <code>EV_VERSION_MAJOR</code> and <code>EV_VERSION_MINOR</code>, which specify the
109 version of the library your program was compiled against.</p>
110 <p>Usually, its a good idea to terminate if the major versions mismatch,
111 as this indicates an incompatible change. Minor versions are usually
112 compatible to older versions, so a larger minor version alone is usually
115 <dt>ev_set_allocator (void *(*cb)(void *ptr, long size))</dt>
117 <p>Sets the allocation function to use (the prototype is similar to the
118 realloc function). It is used to allocate and free memory (no surprises
119 here). If it returns zero when memory needs to be allocated, the library
120 might abort or take some potentially destructive action. The default is
121 your system realloc function.</p>
122 <p>You could override this function in high-availability programs to, say,
123 free some memory if it cannot allocate memory, to use a special allocator,
124 or even to sleep a while and retry until some memory is available.</p>
126 <dt>ev_set_syserr_cb (void (*cb)(const char *msg));</dt>
128 <p>Set the callback function to call on a retryable syscall error (such
129 as failed select, poll, epoll_wait). The message is a printable string
130 indicating the system call or subsystem causing the problem. If this
131 callback is set, then libev will expect it to remedy the sitution, no
132 matter what, when it returns. That is, libev will geenrally retry the
133 requested operation, or, if the condition doesn't go away, do bad stuff
139 <h1 id="FUNCTIONS_CONTROLLING_THE_EVENT_LOOP">FUNCTIONS CONTROLLING THE EVENT LOOP</h1><p><a href="#TOP" class="toplink">Top</a></p>
140 <div id="FUNCTIONS_CONTROLLING_THE_EVENT_LOOP-2">
141 <p>An event loop is described by a <code>struct ev_loop *</code>. The library knows two
142 types of such loops, the <i>default</i> loop, which supports signals and child
143 events, and dynamically created loops which do not.</p>
144 <p>If you use threads, a common model is to run the default event loop
145 in your main thread (or in a separate thrad) and for each thread you
146 create, you also create another event loop. Libev itself does no lockign
147 whatsoever, so if you mix calls to different event loops, make sure you
148 lock (this is usually a bad idea, though, even if done right).</p>
150 <dt>struct ev_loop *ev_default_loop (unsigned int flags)</dt>
152 <p>This will initialise the default event loop if it hasn't been initialised
153 yet and return it. If the default loop could not be initialised, returns
154 false. If it already was initialised it simply returns it (and ignores the
156 <p>If you don't know what event loop to use, use the one returned from this
158 <p>The flags argument can be used to specify special behaviour or specific
159 backends to use, and is usually specified as 0 (or EVFLAG_AUTO)</p>
160 <p>It supports the following flags:</p>
165 <p>The default flags value. Use this if you have no clue (its the right
166 thing, believe me).</p>
168 <dt>EVFLAG_NOENV</dt>
170 <p>If this flag bit is ored into the flag value then libev will <i>not</i> look
171 at the environment variable <code>LIBEV_FLAGS</code>. Otherwise (the default), this
172 environment variable will override the flags completely. This is useful
173 to try out specific backends to tets their performance, or to work around
176 <dt>EVMETHOD_SELECT portable select backend</dt>
177 <dt>EVMETHOD_POLL poll backend (everywhere except windows)</dt>
178 <dt>EVMETHOD_EPOLL linux only</dt>
179 <dt>EVMETHOD_KQUEUE some bsds only</dt>
180 <dt>EVMETHOD_DEVPOLL solaris 8 only</dt>
181 <dt>EVMETHOD_PORT solaris 10 only</dt>
183 <p>If one or more of these are ored into the flags value, then only these
184 backends will be tried (in the reverse order as given here). If one are
185 specified, any backend will do.</p>
190 <dt>struct ev_loop *ev_loop_new (unsigned int flags)</dt>
192 <p>Similar to <code>ev_default_loop</code>, but always creates a new event loop that is
193 always distinct from the default loop. Unlike the default loop, it cannot
194 handle signal and child watchers, and attempts to do so will be greeted by
195 undefined behaviour (or a failed assertion if assertions are enabled).</p>
197 <dt>ev_default_destroy ()</dt>
199 <p>Destroys the default loop again (frees all memory and kernel state
200 etc.). This stops all registered event watchers (by not touching them in
201 any way whatsoever, although you cnanot rely on this :).</p>
203 <dt>ev_loop_destroy (loop)</dt>
205 <p>Like <code>ev_default_destroy</code>, but destroys an event loop created by an
206 earlier call to <code>ev_loop_new</code>.</p>
208 <dt>ev_default_fork ()</dt>
210 <p>This function reinitialises the kernel state for backends that have
211 one. Despite the name, you can call it anytime, but it makes most sense
212 after forking, in either the parent or child process (or both, but that
213 again makes little sense).</p>
214 <p>You <i>must</i> call this function after forking if and only if you want to
215 use the event library in both processes. If you just fork+exec, you don't
217 <p>The function itself is quite fast and its usually not a problem to call
218 it just in case after a fork. To make this easy, the function will fit in
219 quite nicely into a call to <code>pthread_atfork</code>:</p>
220 <pre> pthread_atfork (0, 0, ev_default_fork);
224 <dt>ev_loop_fork (loop)</dt>
226 <p>Like <code>ev_default_fork</code>, but acts on an event loop created by
227 <code>ev_loop_new</code>. Yes, you have to call this on every allocated event loop
228 after fork, and how you do this is entirely your own problem.</p>
230 <dt>unsigned int ev_method (loop)</dt>
232 <p>Returns one of the <code>EVMETHOD_*</code> flags indicating the event backend in
235 <dt>ev_tstamp = ev_now (loop)</dt>
237 <p>Returns the current "event loop time", which is the time the event loop
238 got events and started processing them. This timestamp does not change
239 as long as callbacks are being processed, and this is also the base time
240 used for relative timers. You can treat it as the timestamp of the event
241 occuring (or more correctly, the mainloop finding out about it).</p>
243 <dt>ev_loop (loop, int flags)</dt>
245 <p>Finally, this is it, the event handler. This function usually is called
246 after you initialised all your watchers and you want to start handling
248 <p>If the flags argument is specified as 0, it will not return until either
249 no event watchers are active anymore or <code>ev_unloop</code> was called.</p>
250 <p>A flags value of <code>EVLOOP_NONBLOCK</code> will look for new events, will handle
251 those events and any outstanding ones, but will not block your process in
252 case there are no events.</p>
253 <p>A flags value of <code>EVLOOP_ONESHOT</code> will look for new events (waiting if
254 neccessary) and will handle those and any outstanding ones. It will block
255 your process until at least one new event arrives.</p>
256 <p>This flags value could be used to implement alternative looping
257 constructs, but the <code>prepare</code> and <code>check</code> watchers provide a better and
258 more generic mechanism.</p>
260 <dt>ev_unloop (loop, how)</dt>
262 <p>Can be used to make a call to <code>ev_loop</code> return early. The <code>how</code> argument
263 must be either <code>EVUNLOOP_ONCE</code>, which will make the innermost <code>ev_loop</code>
264 call return, or <code>EVUNLOOP_ALL</code>, which will make all nested <code>ev_loop</code>
267 <dt>ev_ref (loop)</dt>
268 <dt>ev_unref (loop)</dt>
270 <p>Ref/unref can be used to add or remove a refcount on the event loop: Every
271 watcher keeps one reference. If you have a long-runing watcher you never
272 unregister that should not keep ev_loop from running, ev_unref() after
273 starting, and ev_ref() before stopping it. Libev itself uses this for
274 example for its internal signal pipe: It is not visible to you as a user
275 and should not keep <code>ev_loop</code> from exiting if the work is done. It is
276 also an excellent way to do this for generic recurring timers or from
277 within third-party libraries. Just remember to unref after start and ref
283 <h1 id="ANATOMY_OF_A_WATCHER">ANATOMY OF A WATCHER</h1><p><a href="#TOP" class="toplink">Top</a></p>
284 <div id="ANATOMY_OF_A_WATCHER_CONTENT">
285 <p>A watcher is a structure that you create and register to record your
286 interest in some event. For instance, if you want to wait for STDIN to
287 become readable, you would create an ev_io watcher for that:</p>
288 <pre> static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents)
291 ev_unloop (loop, EVUNLOOP_ALL);
294 struct ev_loop *loop = ev_default_loop (0);
295 struct ev_io stdin_watcher;
296 ev_init (&stdin_watcher, my_cb);
297 ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
298 ev_io_start (loop, &stdin_watcher);
302 <p>As you can see, you are responsible for allocating the memory for your
303 watcher structures (and it is usually a bad idea to do this on the stack,
304 although this can sometimes be quite valid).</p>
305 <p>Each watcher structure must be initialised by a call to <code>ev_init
306 (watcher *, callback)</code>, which expects a callback to be provided. This
307 callback gets invoked each time the event occurs (or, in the case of io
308 watchers, each time the event loop detects that the file descriptor given
309 is readable and/or writable).</p>
310 <p>Each watcher type has its own <code>ev_<type>_set (watcher *, ...)</code> macro
311 with arguments specific to this watcher type. There is also a macro
312 to combine initialisation and setting in one call: <code>ev_<type>_init
313 (watcher *, callback, ...)</code>.</p>
314 <p>To make the watcher actually watch out for events, you have to start it
315 with a watcher-specific start function (<code>ev_<type>_start (loop, watcher
316 *)</code>), and you can stop watching for events at any time by calling the
317 corresponding stop function (<code>ev_<type>_stop (loop, watcher *)</code>.</p>
318 <p>As long as your watcher is active (has been started but not stopped) you
319 must not touch the values stored in it. Most specifically you must never
320 reinitialise it or call its set method.</p>
321 <p>You cna check wether an event is active by calling the <code>ev_is_active
322 (watcher *)</code> macro. To see wether an event is outstanding (but the
323 callback for it has not been called yet) you cna use the <code>ev_is_pending
324 (watcher *)</code> macro.</p>
325 <p>Each and every callback receives the event loop pointer as first, the
326 registered watcher structure as second, and a bitset of received events as
328 <p>The rceeived events usually include a single bit per event type received
329 (you can receive multiple events at the same time). The possible bit masks
335 <p>The file descriptor in the ev_io watcher has become readable and/or
340 <p>The ev_timer watcher has timed out.</p>
344 <p>The ev_periodic watcher has timed out.</p>
348 <p>The signal specified in the ev_signal watcher has been received by a thread.</p>
352 <p>The pid specified in the ev_child watcher has received a status change.</p>
356 <p>The ev_idle watcher has determined that you have nothing better to do.</p>
361 <p>All ev_prepare watchers are invoked just <i>before</i> <code>ev_loop</code> starts
362 to gather new events, and all ev_check watchers are invoked just after
363 <code>ev_loop</code> has gathered them, but before it invokes any callbacks for any
364 received events. Callbacks of both watcher types can start and stop as
365 many watchers as they want, and all of them will be taken into account
366 (for example, a ev_prepare watcher might start an idle watcher to keep
367 <code>ev_loop</code> from blocking).</p>
371 <p>An unspecified error has occured, the watcher has been stopped. This might
372 happen because the watcher could not be properly started because libev
373 ran out of memory, a file descriptor was found to be closed or any other
374 problem. You best act on it by reporting the problem and somehow coping
375 with the watcher being stopped.</p>
376 <p>Libev will usually signal a few "dummy" events together with an error,
377 for example it might indicate that a fd is readable or writable, and if
378 your callbacks is well-written it can just attempt the operation and cope
379 with the error from read() or write(). This will not work in multithreaded
380 programs, though, so beware.</p>
385 <h2 id="ASSOCIATING_CUSTOM_DATA_WITH_A_WATCH">ASSOCIATING CUSTOM DATA WITH A WATCHER</h2>
386 <div id="ASSOCIATING_CUSTOM_DATA_WITH_A_WATCH-2">
387 <p>Each watcher has, by default, a member <code>void *data</code> that you can change
388 and read at any time, libev will completely ignore it. This cna be used
389 to associate arbitrary data with your watcher. If you need more data and
390 don't want to allocate memory and store a pointer to it in that data
391 member, you can also "subclass" the watcher type and provide your own
398 struct whatever *mostinteresting;
402 <p>And since your callback will be called with a pointer to the watcher, you
403 can cast it back to your own type:</p>
404 <pre> static void my_cb (struct ev_loop *loop, struct ev_io *w_, int revents)
406 struct my_io *w = (struct my_io *)w_;
411 <p>More interesting and less C-conformant ways of catsing your callback type
412 have been omitted....</p>
419 <h1 id="WATCHER_TYPES">WATCHER TYPES</h1><p><a href="#TOP" class="toplink">Top</a></p>
420 <div id="WATCHER_TYPES_CONTENT">
421 <p>This section describes each watcher in detail, but will not repeat
422 information given in the last section.</p>
425 <h2 id="struct_ev_io_is_my_file_descriptor_r">struct ev_io - is my file descriptor readable or writable</h2>
426 <div id="struct_ev_io_is_my_file_descriptor_r-2">
427 <p>I/O watchers check wether a file descriptor is readable or writable
428 in each iteration of the event loop (This behaviour is called
429 level-triggering because you keep receiving events as long as the
430 condition persists. Remember you cna stop the watcher if you don't want to
431 act on the event and neither want to receive future events).</p>
433 <dt>ev_io_init (ev_io *, callback, int fd, int events)</dt>
434 <dt>ev_io_set (ev_io *, int fd, int events)</dt>
436 <p>Configures an ev_io watcher. The fd is the file descriptor to rceeive
437 events for and events is either <code>EV_READ</code>, <code>EV_WRITE</code> or <code>EV_READ |
438 EV_WRITE</code> to receive the given events.</p>
443 <h2 id="struct_ev_timer_relative_and_optiona">struct ev_timer - relative and optionally recurring timeouts</h2>
444 <div id="struct_ev_timer_relative_and_optiona-2">
445 <p>Timer watchers are simple relative timers that generate an event after a
446 given time, and optionally repeating in regular intervals after that.</p>
447 <p>The timers are based on real time, that is, if you register an event that
448 times out after an hour and youreset your system clock to last years
449 time, it will still time out after (roughly) and hour. "Roughly" because
450 detecting time jumps is hard, and soem inaccuracies are unavoidable (the
451 monotonic clock option helps a lot here).</p>
453 <dt>ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)</dt>
454 <dt>ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)</dt>
456 <p>Configure the timer to trigger after <code>after</code> seconds. If <code>repeat</code> is
457 <code>0.</code>, then it will automatically be stopped. If it is positive, then the
458 timer will automatically be configured to trigger again <code>repeat</code> seconds
459 later, again, and again, until stopped manually.</p>
460 <p>The timer itself will do a best-effort at avoiding drift, that is, if you
461 configure a timer to trigger every 10 seconds, then it will trigger at
462 exactly 10 second intervals. If, however, your program cannot keep up with
463 the timer (ecause it takes longer than those 10 seconds to do stuff) the
464 timer will not fire more than once per event loop iteration.</p>
466 <dt>ev_timer_again (loop)</dt>
468 <p>This will act as if the timer timed out and restart it again if it is
469 repeating. The exact semantics are:</p>
470 <p>If the timer is started but nonrepeating, stop it.</p>
471 <p>If the timer is repeating, either start it if necessary (with the repeat
472 value), or reset the running timer to the repeat value.</p>
473 <p>This sounds a bit complicated, but here is a useful and typical
474 example: Imagine you have a tcp connection and you want a so-called idle
475 timeout, that is, you want to be called when there have been, say, 60
476 seconds of inactivity on the socket. The easiest way to do this is to
477 configure an ev_timer with after=repeat=60 and calling ev_timer_again each
478 time you successfully read or write some data. If you go into an idle
479 state where you do not expect data to travel on the socket, you can stop
480 the timer, and again will automatically restart it if need be.</p>
485 <h2 id="ev_periodic">ev_periodic</h2>
486 <div id="ev_periodic_CONTENT">
487 <p>Periodic watchers are also timers of a kind, but they are very versatile
488 (and unfortunately a bit complex).</p>
489 <p>Unlike ev_timer's, they are not based on real time (or relative time)
490 but on wallclock time (absolute time). You can tell a periodic watcher
491 to trigger "at" some specific point in time. For example, if you tell a
492 periodic watcher to trigger in 10 seconds (by specifiying e.g. c<ev_now ()
493 + 10.>) and then reset your system clock to the last year, then it will
494 take a year to trigger the event (unlike an ev_timer, which would trigger
495 roughly 10 seconds later and of course not if you reset your system time
497 <p>They can also be used to implement vastly more complex timers, such as
498 triggering an event on eahc midnight, local time.</p>
500 <dt>ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)</dt>
501 <dt>ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)</dt>
503 <p>Lots of arguments, lets sort it out... There are basically three modes of
504 operation, and we will explain them from simplest to complex:</p>
511 <dt>* absolute timer (interval = reschedule_cb = 0)</dt>
513 <p>In this configuration the watcher triggers an event at the wallclock time
514 <code>at</code> and doesn't repeat. It will not adjust when a time jump occurs,
515 that is, if it is to be run at January 1st 2011 then it will run when the
516 system time reaches or surpasses this time.</p>
518 <dt>* non-repeating interval timer (interval > 0, reschedule_cb = 0)</dt>
520 <p>In this mode the watcher will always be scheduled to time out at the next
521 <code>at + N * interval</code> time (for some integer N) and then repeat, regardless
522 of any time jumps.</p>
523 <p>This can be used to create timers that do not drift with respect to system
525 <pre> ev_periodic_set (&periodic, 0., 3600., 0);
528 <p>This doesn't mean there will always be 3600 seconds in between triggers,
529 but only that the the callback will be called when the system time shows a
530 full hour (UTC), or more correct, when the system time is evenly divisible
532 <p>Another way to think about it (for the mathematically inclined) is that
533 ev_periodic will try to run the callback in this mode at the next possible
534 time where <code>time = at (mod interval)</code>, regardless of any time jumps.</p>
536 <dt>* manual reschedule mode (reschedule_cb = callback)</dt>
538 <p>In this mode the values for <code>interval</code> and <code>at</code> are both being
539 ignored. Instead, each time the periodic watcher gets scheduled, the
540 reschedule callback will be called with the watcher as first, and the
541 current time as second argument.</p>
542 <p>NOTE: <i>This callback MUST NOT stop or destroy the periodic or any other
543 periodic watcher, ever, or make any event loop modificstions</i>. If you need
544 to stop it, return 1e30 (or so, fudge fudge) and stop it afterwards.</p>
545 <p>Its prototype is c<ev_tstamp (*reschedule_cb)(struct ev_periodic *w,
546 ev_tstamp now)>, e.g.:</p>
547 <pre> static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)
553 <p>It must return the next time to trigger, based on the passed time value
554 (that is, the lowest time value larger than to the second argument). It
555 will usually be called just before the callback will be triggered, but
556 might be called at other times, too.</p>
557 <p>This can be used to create very complex timers, such as a timer that
558 triggers on each midnight, local time. To do this, you would calculate the
559 next midnight after <code>now</code> and return the timestamp value for this. How you do this
560 is, again, up to you (but it is not trivial).</p>
565 <dt>ev_periodic_again (loop, ev_periodic *)</dt>
567 <p>Simply stops and restarts the periodic watcher again. This is only useful
568 when you changed some parameters or the reschedule callback would return
569 a different time than the last time it was called (e.g. in a crond like
570 program when the crontabs have changed).</p>
575 <h2 id="ev_signal_signal_me_when_a_signal_ge">ev_signal - signal me when a signal gets signalled</h2>
576 <div id="ev_signal_signal_me_when_a_signal_ge-2">
577 <p>Signal watchers will trigger an event when the process receives a specific
578 signal one or more times. Even though signals are very asynchronous, libev
579 will try its best to deliver signals synchronously, i.e. as part of the
580 normal event processing, like any other event.</p>
581 <p>You cna configure as many watchers as you like per signal. Only when the
582 first watcher gets started will libev actually register a signal watcher
583 with the kernel (thus it coexists with your own signal handlers as long
584 as you don't register any with libev). Similarly, when the last signal
585 watcher for a signal is stopped libev will reset the signal handler to
586 SIG_DFL (regardless of what it was set to before).</p>
588 <dt>ev_signal_init (ev_signal *, callback, int signum)</dt>
589 <dt>ev_signal_set (ev_signal *, int signum)</dt>
591 <p>Configures the watcher to trigger on the given signal number (usually one
592 of the <code>SIGxxx</code> constants).</p>
597 <h2 id="ev_child_wait_for_pid_status_changes">ev_child - wait for pid status changes</h2>
598 <div id="ev_child_wait_for_pid_status_changes-2">
599 <p>Child watchers trigger when your process receives a SIGCHLD in response to
600 some child status changes (most typically when a child of yours dies).</p>
602 <dt>ev_child_init (ev_child *, callback, int pid)</dt>
603 <dt>ev_child_set (ev_child *, int pid)</dt>
605 <p>Configures the watcher to wait for status changes of process <code>pid</code> (or
606 <i>any</i> process if <code>pid</code> is specified as <code>0</code>). The callback can look
607 at the <code>rstatus</code> member of the <code>ev_child</code> watcher structure to see
608 the status word (use the macros from <code>sys/wait.h</code>). The <code>rpid</code> member
609 contains the pid of the process causing the status change.</p>
614 <h2 id="ev_idle_when_you_ve_got_nothing_bett">ev_idle - when you've got nothing better to do</h2>
615 <div id="ev_idle_when_you_ve_got_nothing_bett-2">
616 <p>Idle watchers trigger events when there are no other I/O or timer (or
617 periodic) events pending. That is, as long as your process is busy
618 handling sockets or timeouts it will not be called. But when your process
619 is idle all idle watchers are being called again and again - until
620 stopped, that is, or your process receives more events.</p>
621 <p>The most noteworthy effect is that as long as any idle watchers are
622 active, the process will not block when waiting for new events.</p>
623 <p>Apart from keeping your process non-blocking (which is a useful
624 effect on its own sometimes), idle watchers are a good place to do
625 "pseudo-background processing", or delay processing stuff to after the
626 event loop has handled all outstanding events.</p>
628 <dt>ev_idle_init (ev_signal *, callback)</dt>
630 <p>Initialises and configures the idle watcher - it has no parameters of any
631 kind. There is a <code>ev_idle_set</code> macro, but using it is utterly pointless,
637 <h2 id="prepare_and_check_your_hooks_into_th">prepare and check - your hooks into the event loop</h2>
638 <div id="prepare_and_check_your_hooks_into_th-2">
639 <p>Prepare and check watchers usually (but not always) are used in
640 tandom. Prepare watchers get invoked before the process blocks and check
641 watchers afterwards.</p>
642 <p>Their main purpose is to integrate other event mechanisms into libev. This
643 could be used, for example, to track variable changes, implement your own
644 watchers, integrate net-snmp or a coroutine library and lots more.</p>
645 <p>This is done by examining in each prepare call which file descriptors need
646 to be watched by the other library, registering ev_io watchers for them
647 and starting an ev_timer watcher for any timeouts (many libraries provide
648 just this functionality). Then, in the check watcher you check for any
649 events that occured (by making your callbacks set soem flags for example)
650 and call back into the library.</p>
651 <p>As another example, the perl Coro module uses these hooks to integrate
652 coroutines into libev programs, by yielding to other active coroutines
653 during each prepare and only letting the process block if no coroutines
654 are ready to run.</p>
656 <dt>ev_prepare_init (ev_prepare *, callback)</dt>
657 <dt>ev_check_init (ev_check *, callback)</dt>
659 <p>Initialises and configures the prepare or check watcher - they have no
660 parameters of any kind. There are <code>ev_prepare_set</code> and <code>ev_check_set</code>
661 macros, but using them is utterly, utterly pointless.</p>
666 <h1 id="OTHER_FUNCTIONS">OTHER FUNCTIONS</h1><p><a href="#TOP" class="toplink">Top</a></p>
667 <div id="OTHER_FUNCTIONS_CONTENT">
668 <p>There are some other fucntions of possible interest. Described. Here. Now.</p>
670 <dt>ev_once (loop, int fd, int events, ev_tstamp timeout, callback)</dt>
672 <p>This function combines a simple timer and an I/O watcher, calls your
673 callback on whichever event happens first and automatically stop both
674 watchers. This is useful if you want to wait for a single event on an fd
675 or timeout without havign to allocate/configure/start/stop/free one or
676 more watchers yourself.</p>
677 <p>If <code>fd</code> is less than 0, then no I/O watcher will be started and events is
678 ignored. Otherwise, an ev_io watcher for the given <code>fd</code> and <code>events</code> set
679 will be craeted and started.</p>
680 <p>If <code>timeout</code> is less than 0, then no timeout watcher will be
681 started. Otherwise an ev_timer watcher with after = <code>timeout</code> (and repeat
682 = 0) will be started.</p>
683 <p>The callback has the type <code>void (*cb)(int revents, void *arg)</code> and
684 gets passed an events set (normally a combination of EV_ERROR, EV_READ,
685 EV_WRITE or EV_TIMEOUT) and the <code>arg</code> value passed to <code>ev_once</code>:</p>
686 <pre> static void stdin_ready (int revents, void *arg)
688 if (revents & EV_TIMEOUT)
689 /* doh, nothing entered */
690 else if (revents & EV_READ)
691 /* stdin might have data for us, joy! */
694 ev_once (STDIN_FILENO, EV_READm 10., stdin_ready, 0);
698 <dt>ev_feed_event (loop, watcher, int events)</dt>
700 <p>Feeds the given event set into the event loop, as if the specified event
701 has happened for the specified watcher (which must be a pointer to an
702 initialised but not necessarily active event watcher).</p>
704 <dt>ev_feed_fd_event (loop, int fd, int revents)</dt>
706 <p>Feed an event on the given fd, as if a file descriptor backend detected it.</p>
708 <dt>ev_feed_signal_event (loop, int signum)</dt>
710 <p>Feed an event as if the given signal occured (loop must be the default loop!).</p>
715 <h1 id="AUTHOR">AUTHOR</h1><p><a href="#TOP" class="toplink">Top</a></p>
716 <div id="AUTHOR_CONTENT">
717 <p>Marc Lehmann <libev@schmorp.de>.</p>
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