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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_to_cron_or_not_to_cron_i">ev_periodic - to cron or not to cron it</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 with 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). It also is quite
77 fast (see this <a href="http://libev.schmorp.de/bench.html">benchmark</a> comparing
78 it to libevent for example).</p>
81 <h1 id="CONVENTIONS">CONVENTIONS</h1><p><a href="#TOP" class="toplink">Top</a></p>
82 <div id="CONVENTIONS_CONTENT">
83 <p>Libev is very configurable. In this manual the default configuration
84 will be described, which supports multiple event loops. For more info
85 about various configuration options please have a look at the file
86 <cite>README.embed</cite> in the libev distribution. If libev was configured without
87 support for multiple event loops, then all functions taking an initial
88 argument of name <code>loop</code> (which is always of type <code>struct ev_loop *</code>)
89 will not have this argument.</p>
92 <h1 id="TIME_AND_OTHER_GLOBAL_FUNCTIONS">TIME AND OTHER GLOBAL FUNCTIONS</h1><p><a href="#TOP" class="toplink">Top</a></p>
93 <div id="TIME_AND_OTHER_GLOBAL_FUNCTIONS_CONT">
94 <p>Libev represents time as a single floating point number, representing the
95 (fractional) number of seconds since the (POSIX) epoch (somewhere near
96 the beginning of 1970, details are complicated, don't ask). This type is
97 called <code>ev_tstamp</code>, which is what you should use too. It usually aliases
98 to the double type in C.</p>
100 <dt>ev_tstamp ev_time ()</dt>
102 <p>Returns the current time as libev would use it.</p>
104 <dt>int ev_version_major ()</dt>
105 <dt>int ev_version_minor ()</dt>
107 <p>You can find out the major and minor version numbers of the library
108 you linked against by calling the functions <code>ev_version_major</code> and
109 <code>ev_version_minor</code>. If you want, you can compare against the global
110 symbols <code>EV_VERSION_MAJOR</code> and <code>EV_VERSION_MINOR</code>, which specify the
111 version of the library your program was compiled against.</p>
112 <p>Usually, its a good idea to terminate if the major versions mismatch,
113 as this indicates an incompatible change. Minor versions are usually
114 compatible to older versions, so a larger minor version alone is usually
117 <dt>ev_set_allocator (void *(*cb)(void *ptr, long size))</dt>
119 <p>Sets the allocation function to use (the prototype is similar to the
120 realloc C function, the semantics are identical). It is used to allocate
121 and free memory (no surprises here). If it returns zero when memory
122 needs to be allocated, the library might abort or take some potentially
123 destructive action. The default is your system realloc function.</p>
124 <p>You could override this function in high-availability programs to, say,
125 free some memory if it cannot allocate memory, to use a special allocator,
126 or even to sleep a while and retry until some memory is available.</p>
128 <dt>ev_set_syserr_cb (void (*cb)(const char *msg));</dt>
130 <p>Set the callback function to call on a retryable syscall error (such
131 as failed select, poll, epoll_wait). The message is a printable string
132 indicating the system call or subsystem causing the problem. If this
133 callback is set, then libev will expect it to remedy the sitution, no
134 matter what, when it returns. That is, libev will generally retry the
135 requested operation, or, if the condition doesn't go away, do bad stuff
141 <h1 id="FUNCTIONS_CONTROLLING_THE_EVENT_LOOP">FUNCTIONS CONTROLLING THE EVENT LOOP</h1><p><a href="#TOP" class="toplink">Top</a></p>
142 <div id="FUNCTIONS_CONTROLLING_THE_EVENT_LOOP-2">
143 <p>An event loop is described by a <code>struct ev_loop *</code>. The library knows two
144 types of such loops, the <i>default</i> loop, which supports signals and child
145 events, and dynamically created loops which do not.</p>
146 <p>If you use threads, a common model is to run the default event loop
147 in your main thread (or in a separate thrad) and for each thread you
148 create, you also create another event loop. Libev itself does no locking
149 whatsoever, so if you mix calls to the same event loop in different
150 threads, make sure you lock (this is usually a bad idea, though, even if
151 done correctly, because its hideous and inefficient).</p>
153 <dt>struct ev_loop *ev_default_loop (unsigned int flags)</dt>
155 <p>This will initialise the default event loop if it hasn't been initialised
156 yet and return it. If the default loop could not be initialised, returns
157 false. If it already was initialised it simply returns it (and ignores the
159 <p>If you don't know what event loop to use, use the one returned from this
161 <p>The flags argument can be used to specify special behaviour or specific
162 backends to use, and is usually specified as 0 (or EVFLAG_AUTO)</p>
163 <p>It supports the following flags:</p>
168 <p>The default flags value. Use this if you have no clue (its the right
169 thing, believe me).</p>
171 <dt>EVFLAG_NOENV</dt>
173 <p>If this flag bit is ored into the flag value then libev will <i>not</i> look
174 at the environment variable <code>LIBEV_FLAGS</code>. Otherwise (the default), this
175 environment variable will override the flags completely. This is useful
176 to try out specific backends to tets their performance, or to work around
179 <dt>EVMETHOD_SELECT portable select backend</dt>
180 <dt>EVMETHOD_POLL poll backend (everywhere except windows)</dt>
181 <dt>EVMETHOD_EPOLL linux only</dt>
182 <dt>EVMETHOD_KQUEUE some bsds only</dt>
183 <dt>EVMETHOD_DEVPOLL solaris 8 only</dt>
184 <dt>EVMETHOD_PORT solaris 10 only</dt>
186 <p>If one or more of these are ored into the flags value, then only these
187 backends will be tried (in the reverse order as given here). If one are
188 specified, any backend will do.</p>
193 <dt>struct ev_loop *ev_loop_new (unsigned int flags)</dt>
195 <p>Similar to <code>ev_default_loop</code>, but always creates a new event loop that is
196 always distinct from the default loop. Unlike the default loop, it cannot
197 handle signal and child watchers, and attempts to do so will be greeted by
198 undefined behaviour (or a failed assertion if assertions are enabled).</p>
200 <dt>ev_default_destroy ()</dt>
202 <p>Destroys the default loop again (frees all memory and kernel state
203 etc.). This stops all registered event watchers (by not touching them in
204 any way whatsoever, although you cnanot rely on this :).</p>
206 <dt>ev_loop_destroy (loop)</dt>
208 <p>Like <code>ev_default_destroy</code>, but destroys an event loop created by an
209 earlier call to <code>ev_loop_new</code>.</p>
211 <dt>ev_default_fork ()</dt>
213 <p>This function reinitialises the kernel state for backends that have
214 one. Despite the name, you can call it anytime, but it makes most sense
215 after forking, in either the parent or child process (or both, but that
216 again makes little sense).</p>
217 <p>You <i>must</i> call this function after forking if and only if you want to
218 use the event library in both processes. If you just fork+exec, you don't
220 <p>The function itself is quite fast and its usually not a problem to call
221 it just in case after a fork. To make this easy, the function will fit in
222 quite nicely into a call to <code>pthread_atfork</code>:</p>
223 <pre> pthread_atfork (0, 0, ev_default_fork);
227 <dt>ev_loop_fork (loop)</dt>
229 <p>Like <code>ev_default_fork</code>, but acts on an event loop created by
230 <code>ev_loop_new</code>. Yes, you have to call this on every allocated event loop
231 after fork, and how you do this is entirely your own problem.</p>
233 <dt>unsigned int ev_method (loop)</dt>
235 <p>Returns one of the <code>EVMETHOD_*</code> flags indicating the event backend in
238 <dt>ev_tstamp = ev_now (loop)</dt>
240 <p>Returns the current "event loop time", which is the time the event loop
241 got events and started processing them. This timestamp does not change
242 as long as callbacks are being processed, and this is also the base time
243 used for relative timers. You can treat it as the timestamp of the event
244 occuring (or more correctly, the mainloop finding out about it).</p>
246 <dt>ev_loop (loop, int flags)</dt>
248 <p>Finally, this is it, the event handler. This function usually is called
249 after you initialised all your watchers and you want to start handling
251 <p>If the flags argument is specified as 0, it will not return until either
252 no event watchers are active anymore or <code>ev_unloop</code> was called.</p>
253 <p>A flags value of <code>EVLOOP_NONBLOCK</code> will look for new events, will handle
254 those events and any outstanding ones, but will not block your process in
255 case there are no events.</p>
256 <p>A flags value of <code>EVLOOP_ONESHOT</code> will look for new events (waiting if
257 neccessary) and will handle those and any outstanding ones. It will block
258 your process until at least one new event arrives.</p>
259 <p>This flags value could be used to implement alternative looping
260 constructs, but the <code>prepare</code> and <code>check</code> watchers provide a better and
261 more generic mechanism.</p>
263 <dt>ev_unloop (loop, how)</dt>
265 <p>Can be used to make a call to <code>ev_loop</code> return early. The <code>how</code> argument
266 must be either <code>EVUNLOOP_ONCE</code>, which will make the innermost <code>ev_loop</code>
267 call return, or <code>EVUNLOOP_ALL</code>, which will make all nested <code>ev_loop</code>
270 <dt>ev_ref (loop)</dt>
271 <dt>ev_unref (loop)</dt>
273 <p>Ref/unref can be used to add or remove a refcount on the event loop: Every
274 watcher keeps one reference. If you have a long-runing watcher you never
275 unregister that should not keep ev_loop from running, ev_unref() after
276 starting, and ev_ref() before stopping it. Libev itself uses this for
277 example for its internal signal pipe: It is not visible to you as a user
278 and should not keep <code>ev_loop</code> from exiting if the work is done. It is
279 also an excellent way to do this for generic recurring timers or from
280 within third-party libraries. Just remember to unref after start and ref
286 <h1 id="ANATOMY_OF_A_WATCHER">ANATOMY OF A WATCHER</h1><p><a href="#TOP" class="toplink">Top</a></p>
287 <div id="ANATOMY_OF_A_WATCHER_CONTENT">
288 <p>A watcher is a structure that you create and register to record your
289 interest in some event. For instance, if you want to wait for STDIN to
290 become readable, you would create an ev_io watcher for that:</p>
291 <pre> static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents)
294 ev_unloop (loop, EVUNLOOP_ALL);
297 struct ev_loop *loop = ev_default_loop (0);
298 struct ev_io stdin_watcher;
299 ev_init (&stdin_watcher, my_cb);
300 ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
301 ev_io_start (loop, &stdin_watcher);
305 <p>As you can see, you are responsible for allocating the memory for your
306 watcher structures (and it is usually a bad idea to do this on the stack,
307 although this can sometimes be quite valid).</p>
308 <p>Each watcher structure must be initialised by a call to <code>ev_init
309 (watcher *, callback)</code>, which expects a callback to be provided. This
310 callback gets invoked each time the event occurs (or, in the case of io
311 watchers, each time the event loop detects that the file descriptor given
312 is readable and/or writable).</p>
313 <p>Each watcher type has its own <code>ev_<type>_set (watcher *, ...)</code> macro
314 with arguments specific to this watcher type. There is also a macro
315 to combine initialisation and setting in one call: <code>ev_<type>_init
316 (watcher *, callback, ...)</code>.</p>
317 <p>To make the watcher actually watch out for events, you have to start it
318 with a watcher-specific start function (<code>ev_<type>_start (loop, watcher
319 *)</code>), and you can stop watching for events at any time by calling the
320 corresponding stop function (<code>ev_<type>_stop (loop, watcher *)</code>.</p>
321 <p>As long as your watcher is active (has been started but not stopped) you
322 must not touch the values stored in it. Most specifically you must never
323 reinitialise it or call its set method.</p>
324 <p>You cna check whether an event is active by calling the <code>ev_is_active
325 (watcher *)</code> macro. To see whether an event is outstanding (but the
326 callback for it has not been called yet) you cna use the <code>ev_is_pending
327 (watcher *)</code> macro.</p>
328 <p>Each and every callback receives the event loop pointer as first, the
329 registered watcher structure as second, and a bitset of received events as
331 <p>The rceeived events usually include a single bit per event type received
332 (you can receive multiple events at the same time). The possible bit masks
338 <p>The file descriptor in the ev_io watcher has become readable and/or
343 <p>The ev_timer watcher has timed out.</p>
347 <p>The ev_periodic watcher has timed out.</p>
351 <p>The signal specified in the ev_signal watcher has been received by a thread.</p>
355 <p>The pid specified in the ev_child watcher has received a status change.</p>
359 <p>The ev_idle watcher has determined that you have nothing better to do.</p>
364 <p>All ev_prepare watchers are invoked just <i>before</i> <code>ev_loop</code> starts
365 to gather new events, and all ev_check watchers are invoked just after
366 <code>ev_loop</code> has gathered them, but before it invokes any callbacks for any
367 received events. Callbacks of both watcher types can start and stop as
368 many watchers as they want, and all of them will be taken into account
369 (for example, a ev_prepare watcher might start an idle watcher to keep
370 <code>ev_loop</code> from blocking).</p>
374 <p>An unspecified error has occured, the watcher has been stopped. This might
375 happen because the watcher could not be properly started because libev
376 ran out of memory, a file descriptor was found to be closed or any other
377 problem. You best act on it by reporting the problem and somehow coping
378 with the watcher being stopped.</p>
379 <p>Libev will usually signal a few "dummy" events together with an error,
380 for example it might indicate that a fd is readable or writable, and if
381 your callbacks is well-written it can just attempt the operation and cope
382 with the error from read() or write(). This will not work in multithreaded
383 programs, though, so beware.</p>
388 <h2 id="ASSOCIATING_CUSTOM_DATA_WITH_A_WATCH">ASSOCIATING CUSTOM DATA WITH A WATCHER</h2>
389 <div id="ASSOCIATING_CUSTOM_DATA_WITH_A_WATCH-2">
390 <p>Each watcher has, by default, a member <code>void *data</code> that you can change
391 and read at any time, libev will completely ignore it. This cna be used
392 to associate arbitrary data with your watcher. If you need more data and
393 don't want to allocate memory and store a pointer to it in that data
394 member, you can also "subclass" the watcher type and provide your own
401 struct whatever *mostinteresting;
405 <p>And since your callback will be called with a pointer to the watcher, you
406 can cast it back to your own type:</p>
407 <pre> static void my_cb (struct ev_loop *loop, struct ev_io *w_, int revents)
409 struct my_io *w = (struct my_io *)w_;
414 <p>More interesting and less C-conformant ways of catsing your callback type
415 have been omitted....</p>
422 <h1 id="WATCHER_TYPES">WATCHER TYPES</h1><p><a href="#TOP" class="toplink">Top</a></p>
423 <div id="WATCHER_TYPES_CONTENT">
424 <p>This section describes each watcher in detail, but will not repeat
425 information given in the last section.</p>
428 <h2 id="struct_ev_io_is_my_file_descriptor_r">struct ev_io - is my file descriptor readable or writable</h2>
429 <div id="struct_ev_io_is_my_file_descriptor_r-2">
430 <p>I/O watchers check whether a file descriptor is readable or writable
431 in each iteration of the event loop (This behaviour is called
432 level-triggering because you keep receiving events as long as the
433 condition persists. Remember you cna stop the watcher if you don't want to
434 act on the event and neither want to receive future events).</p>
436 <dt>ev_io_init (ev_io *, callback, int fd, int events)</dt>
437 <dt>ev_io_set (ev_io *, int fd, int events)</dt>
439 <p>Configures an ev_io watcher. The fd is the file descriptor to rceeive
440 events for and events is either <code>EV_READ</code>, <code>EV_WRITE</code> or <code>EV_READ |
441 EV_WRITE</code> to receive the given events.</p>
446 <h2 id="struct_ev_timer_relative_and_optiona">struct ev_timer - relative and optionally recurring timeouts</h2>
447 <div id="struct_ev_timer_relative_and_optiona-2">
448 <p>Timer watchers are simple relative timers that generate an event after a
449 given time, and optionally repeating in regular intervals after that.</p>
450 <p>The timers are based on real time, that is, if you register an event that
451 times out after an hour and youreset your system clock to last years
452 time, it will still time out after (roughly) and hour. "Roughly" because
453 detecting time jumps is hard, and soem inaccuracies are unavoidable (the
454 monotonic clock option helps a lot here).</p>
456 <dt>ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)</dt>
457 <dt>ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)</dt>
459 <p>Configure the timer to trigger after <code>after</code> seconds. If <code>repeat</code> is
460 <code>0.</code>, then it will automatically be stopped. If it is positive, then the
461 timer will automatically be configured to trigger again <code>repeat</code> seconds
462 later, again, and again, until stopped manually.</p>
463 <p>The timer itself will do a best-effort at avoiding drift, that is, if you
464 configure a timer to trigger every 10 seconds, then it will trigger at
465 exactly 10 second intervals. If, however, your program cannot keep up with
466 the timer (ecause it takes longer than those 10 seconds to do stuff) the
467 timer will not fire more than once per event loop iteration.</p>
469 <dt>ev_timer_again (loop)</dt>
471 <p>This will act as if the timer timed out and restart it again if it is
472 repeating. The exact semantics are:</p>
473 <p>If the timer is started but nonrepeating, stop it.</p>
474 <p>If the timer is repeating, either start it if necessary (with the repeat
475 value), or reset the running timer to the repeat value.</p>
476 <p>This sounds a bit complicated, but here is a useful and typical
477 example: Imagine you have a tcp connection and you want a so-called idle
478 timeout, that is, you want to be called when there have been, say, 60
479 seconds of inactivity on the socket. The easiest way to do this is to
480 configure an ev_timer with after=repeat=60 and calling ev_timer_again each
481 time you successfully read or write some data. If you go into an idle
482 state where you do not expect data to travel on the socket, you can stop
483 the timer, and again will automatically restart it if need be.</p>
488 <h2 id="ev_periodic_to_cron_or_not_to_cron_i">ev_periodic - to cron or not to cron it</h2>
489 <div id="ev_periodic_to_cron_or_not_to_cron_i-2">
490 <p>Periodic watchers are also timers of a kind, but they are very versatile
491 (and unfortunately a bit complex).</p>
492 <p>Unlike ev_timer's, they are not based on real time (or relative time)
493 but on wallclock time (absolute time). You can tell a periodic watcher
494 to trigger "at" some specific point in time. For example, if you tell a
495 periodic watcher to trigger in 10 seconds (by specifiying e.g. c<ev_now ()
496 + 10.>) and then reset your system clock to the last year, then it will
497 take a year to trigger the event (unlike an ev_timer, which would trigger
498 roughly 10 seconds later and of course not if you reset your system time
500 <p>They can also be used to implement vastly more complex timers, such as
501 triggering an event on eahc midnight, local time.</p>
503 <dt>ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)</dt>
504 <dt>ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)</dt>
506 <p>Lots of arguments, lets sort it out... There are basically three modes of
507 operation, and we will explain them from simplest to complex:</p>
514 <dt>* absolute timer (interval = reschedule_cb = 0)</dt>
516 <p>In this configuration the watcher triggers an event at the wallclock time
517 <code>at</code> and doesn't repeat. It will not adjust when a time jump occurs,
518 that is, if it is to be run at January 1st 2011 then it will run when the
519 system time reaches or surpasses this time.</p>
521 <dt>* non-repeating interval timer (interval > 0, reschedule_cb = 0)</dt>
523 <p>In this mode the watcher will always be scheduled to time out at the next
524 <code>at + N * interval</code> time (for some integer N) and then repeat, regardless
525 of any time jumps.</p>
526 <p>This can be used to create timers that do not drift with respect to system
528 <pre> ev_periodic_set (&periodic, 0., 3600., 0);
531 <p>This doesn't mean there will always be 3600 seconds in between triggers,
532 but only that the the callback will be called when the system time shows a
533 full hour (UTC), or more correct, when the system time is evenly divisible
535 <p>Another way to think about it (for the mathematically inclined) is that
536 ev_periodic will try to run the callback in this mode at the next possible
537 time where <code>time = at (mod interval)</code>, regardless of any time jumps.</p>
539 <dt>* manual reschedule mode (reschedule_cb = callback)</dt>
541 <p>In this mode the values for <code>interval</code> and <code>at</code> are both being
542 ignored. Instead, each time the periodic watcher gets scheduled, the
543 reschedule callback will be called with the watcher as first, and the
544 current time as second argument.</p>
545 <p>NOTE: <i>This callback MUST NOT stop or destroy the periodic or any other
546 periodic watcher, ever, or make any event loop modificstions</i>. If you need
547 to stop it, return 1e30 (or so, fudge fudge) and stop it afterwards.</p>
548 <p>Its prototype is c<ev_tstamp (*reschedule_cb)(struct ev_periodic *w,
549 ev_tstamp now)>, e.g.:</p>
550 <pre> static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)
556 <p>It must return the next time to trigger, based on the passed time value
557 (that is, the lowest time value larger than to the second argument). It
558 will usually be called just before the callback will be triggered, but
559 might be called at other times, too.</p>
560 <p>This can be used to create very complex timers, such as a timer that
561 triggers on each midnight, local time. To do this, you would calculate the
562 next midnight after <code>now</code> and return the timestamp value for this. How you do this
563 is, again, up to you (but it is not trivial).</p>
568 <dt>ev_periodic_again (loop, ev_periodic *)</dt>
570 <p>Simply stops and restarts the periodic watcher again. This is only useful
571 when you changed some parameters or the reschedule callback would return
572 a different time than the last time it was called (e.g. in a crond like
573 program when the crontabs have changed).</p>
578 <h2 id="ev_signal_signal_me_when_a_signal_ge">ev_signal - signal me when a signal gets signalled</h2>
579 <div id="ev_signal_signal_me_when_a_signal_ge-2">
580 <p>Signal watchers will trigger an event when the process receives a specific
581 signal one or more times. Even though signals are very asynchronous, libev
582 will try its best to deliver signals synchronously, i.e. as part of the
583 normal event processing, like any other event.</p>
584 <p>You cna configure as many watchers as you like per signal. Only when the
585 first watcher gets started will libev actually register a signal watcher
586 with the kernel (thus it coexists with your own signal handlers as long
587 as you don't register any with libev). Similarly, when the last signal
588 watcher for a signal is stopped libev will reset the signal handler to
589 SIG_DFL (regardless of what it was set to before).</p>
591 <dt>ev_signal_init (ev_signal *, callback, int signum)</dt>
592 <dt>ev_signal_set (ev_signal *, int signum)</dt>
594 <p>Configures the watcher to trigger on the given signal number (usually one
595 of the <code>SIGxxx</code> constants).</p>
600 <h2 id="ev_child_wait_for_pid_status_changes">ev_child - wait for pid status changes</h2>
601 <div id="ev_child_wait_for_pid_status_changes-2">
602 <p>Child watchers trigger when your process receives a SIGCHLD in response to
603 some child status changes (most typically when a child of yours dies).</p>
605 <dt>ev_child_init (ev_child *, callback, int pid)</dt>
606 <dt>ev_child_set (ev_child *, int pid)</dt>
608 <p>Configures the watcher to wait for status changes of process <code>pid</code> (or
609 <i>any</i> process if <code>pid</code> is specified as <code>0</code>). The callback can look
610 at the <code>rstatus</code> member of the <code>ev_child</code> watcher structure to see
611 the status word (use the macros from <code>sys/wait.h</code>). The <code>rpid</code> member
612 contains the pid of the process causing the status change.</p>
617 <h2 id="ev_idle_when_you_ve_got_nothing_bett">ev_idle - when you've got nothing better to do</h2>
618 <div id="ev_idle_when_you_ve_got_nothing_bett-2">
619 <p>Idle watchers trigger events when there are no other I/O or timer (or
620 periodic) events pending. That is, as long as your process is busy
621 handling sockets or timeouts it will not be called. But when your process
622 is idle all idle watchers are being called again and again - until
623 stopped, that is, or your process receives more events.</p>
624 <p>The most noteworthy effect is that as long as any idle watchers are
625 active, the process will not block when waiting for new events.</p>
626 <p>Apart from keeping your process non-blocking (which is a useful
627 effect on its own sometimes), idle watchers are a good place to do
628 "pseudo-background processing", or delay processing stuff to after the
629 event loop has handled all outstanding events.</p>
631 <dt>ev_idle_init (ev_signal *, callback)</dt>
633 <p>Initialises and configures the idle watcher - it has no parameters of any
634 kind. There is a <code>ev_idle_set</code> macro, but using it is utterly pointless,
640 <h2 id="prepare_and_check_your_hooks_into_th">prepare and check - your hooks into the event loop</h2>
641 <div id="prepare_and_check_your_hooks_into_th-2">
642 <p>Prepare and check watchers usually (but not always) are used in
643 tandom. Prepare watchers get invoked before the process blocks and check
644 watchers afterwards.</p>
645 <p>Their main purpose is to integrate other event mechanisms into libev. This
646 could be used, for example, to track variable changes, implement your own
647 watchers, integrate net-snmp or a coroutine library and lots more.</p>
648 <p>This is done by examining in each prepare call which file descriptors need
649 to be watched by the other library, registering ev_io watchers for them
650 and starting an ev_timer watcher for any timeouts (many libraries provide
651 just this functionality). Then, in the check watcher you check for any
652 events that occured (by making your callbacks set soem flags for example)
653 and call back into the library.</p>
654 <p>As another example, the perl Coro module uses these hooks to integrate
655 coroutines into libev programs, by yielding to other active coroutines
656 during each prepare and only letting the process block if no coroutines
657 are ready to run.</p>
659 <dt>ev_prepare_init (ev_prepare *, callback)</dt>
660 <dt>ev_check_init (ev_check *, callback)</dt>
662 <p>Initialises and configures the prepare or check watcher - they have no
663 parameters of any kind. There are <code>ev_prepare_set</code> and <code>ev_check_set</code>
664 macros, but using them is utterly, utterly pointless.</p>
669 <h1 id="OTHER_FUNCTIONS">OTHER FUNCTIONS</h1><p><a href="#TOP" class="toplink">Top</a></p>
670 <div id="OTHER_FUNCTIONS_CONTENT">
671 <p>There are some other fucntions of possible interest. Described. Here. Now.</p>
673 <dt>ev_once (loop, int fd, int events, ev_tstamp timeout, callback)</dt>
675 <p>This function combines a simple timer and an I/O watcher, calls your
676 callback on whichever event happens first and automatically stop both
677 watchers. This is useful if you want to wait for a single event on an fd
678 or timeout without havign to allocate/configure/start/stop/free one or
679 more watchers yourself.</p>
680 <p>If <code>fd</code> is less than 0, then no I/O watcher will be started and events is
681 ignored. Otherwise, an ev_io watcher for the given <code>fd</code> and <code>events</code> set
682 will be craeted and started.</p>
683 <p>If <code>timeout</code> is less than 0, then no timeout watcher will be
684 started. Otherwise an ev_timer watcher with after = <code>timeout</code> (and repeat
685 = 0) will be started.</p>
686 <p>The callback has the type <code>void (*cb)(int revents, void *arg)</code> and
687 gets passed an events set (normally a combination of EV_ERROR, EV_READ,
688 EV_WRITE or EV_TIMEOUT) and the <code>arg</code> value passed to <code>ev_once</code>:</p>
689 <pre> static void stdin_ready (int revents, void *arg)
691 if (revents & EV_TIMEOUT)
692 /* doh, nothing entered */
693 else if (revents & EV_READ)
694 /* stdin might have data for us, joy! */
697 ev_once (STDIN_FILENO, EV_READm 10., stdin_ready, 0);
701 <dt>ev_feed_event (loop, watcher, int events)</dt>
703 <p>Feeds the given event set into the event loop, as if the specified event
704 has happened for the specified watcher (which must be a pointer to an
705 initialised but not necessarily active event watcher).</p>
707 <dt>ev_feed_fd_event (loop, int fd, int revents)</dt>
709 <p>Feed an event on the given fd, as if a file descriptor backend detected it.</p>
711 <dt>ev_feed_signal_event (loop, int signum)</dt>
713 <p>Feed an event as if the given signal occured (loop must be the default loop!).</p>
718 <h1 id="AUTHOR">AUTHOR</h1><p><a href="#TOP" class="toplink">Top</a></p>
719 <div id="AUTHOR_CONTENT">
720 <p>Marc Lehmann <libev@schmorp.de>.</p>
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