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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_REPRESENTATION">TIME REPRESENTATION</a></li>
23 <li><a href="#GLOBAL_FUNCTIONS">GLOBAL FUNCTIONS</a></li>
24 <li><a href="#FUNCTIONS_CONTROLLING_THE_EVENT_LOOP">FUNCTIONS CONTROLLING THE EVENT LOOP</a></li>
25 <li><a href="#ANATOMY_OF_A_WATCHER">ANATOMY OF A WATCHER</a>
26 <ul><li><a href="#ASSOCIATING_CUSTOM_DATA_WITH_A_WATCH">ASSOCIATING CUSTOM DATA WITH A WATCHER</a></li>
29 <li><a href="#WATCHER_TYPES">WATCHER TYPES</a>
30 <ul><li><a href="#code_ev_io_code_is_this_file_descrip"><code>ev_io</code> - is this file descriptor readable or writable</a></li>
31 <li><a href="#code_ev_timer_code_relative_and_opti"><code>ev_timer</code> - relative and optionally recurring timeouts</a></li>
32 <li><a href="#code_ev_periodic_code_to_cron_or_not"><code>ev_periodic</code> - to cron or not to cron</a></li>
33 <li><a href="#code_ev_signal_code_signal_me_when_a"><code>ev_signal</code> - signal me when a signal gets signalled</a></li>
34 <li><a href="#code_ev_child_code_wait_for_pid_stat"><code>ev_child</code> - wait for pid status changes</a></li>
35 <li><a href="#code_ev_idle_code_when_you_ve_got_no"><code>ev_idle</code> - when you've got nothing better to do</a></li>
36 <li><a href="#code_ev_prepare_code_and_code_ev_che"><code>ev_prepare</code> and <code>ev_check</code> - customise your event loop</a></li>
39 <li><a href="#OTHER_FUNCTIONS">OTHER FUNCTIONS</a></li>
40 <li><a href="#AUTHOR">AUTHOR</a>
45 <h1 id="NAME">NAME</h1><p><a href="#TOP" class="toplink">Top</a></p>
46 <div id="NAME_CONTENT">
47 <p>libev - a high performance full-featured event loop written in C</p>
50 <h1 id="SYNOPSIS">SYNOPSIS</h1><p><a href="#TOP" class="toplink">Top</a></p>
51 <div id="SYNOPSIS_CONTENT">
52 <pre> #include <ev.h>
57 <h1 id="DESCRIPTION">DESCRIPTION</h1><p><a href="#TOP" class="toplink">Top</a></p>
58 <div id="DESCRIPTION_CONTENT">
59 <p>Libev is an event loop: you register interest in certain events (such as a
60 file descriptor being readable or a timeout occuring), and it will manage
61 these event sources and provide your program with events.</p>
62 <p>To do this, it must take more or less complete control over your process
63 (or thread) by executing the <i>event loop</i> handler, and will then
64 communicate events via a callback mechanism.</p>
65 <p>You register interest in certain events by registering so-called <i>event
66 watchers</i>, which are relatively small C structures you initialise with the
67 details of the event, and then hand it over to libev by <i>starting</i> the
71 <h1 id="FEATURES">FEATURES</h1><p><a href="#TOP" class="toplink">Top</a></p>
72 <div id="FEATURES_CONTENT">
73 <p>Libev supports select, poll, the linux-specific epoll and the bsd-specific
74 kqueue mechanisms for file descriptor events, relative timers, absolute
75 timers with customised rescheduling, signal events, process status change
76 events (related to SIGCHLD), and event watchers dealing with the event
77 loop mechanism itself (idle, prepare and check watchers). It also is quite
78 fast (see this <a href="http://libev.schmorp.de/bench.html">benchmark</a> comparing
79 it to libevent for example).</p>
82 <h1 id="CONVENTIONS">CONVENTIONS</h1><p><a href="#TOP" class="toplink">Top</a></p>
83 <div id="CONVENTIONS_CONTENT">
84 <p>Libev is very configurable. In this manual the default configuration
85 will be described, which supports multiple event loops. For more info
86 about various configuration options please have a look at the file
87 <cite>README.embed</cite> in the libev distribution. If libev was configured without
88 support for multiple event loops, then all functions taking an initial
89 argument of name <code>loop</code> (which is always of type <code>struct ev_loop *</code>)
90 will not have this argument.</p>
93 <h1 id="TIME_REPRESENTATION">TIME REPRESENTATION</h1><p><a href="#TOP" class="toplink">Top</a></p>
94 <div id="TIME_REPRESENTATION_CONTENT">
95 <p>Libev represents time as a single floating point number, representing the
96 (fractional) number of seconds since the (POSIX) epoch (somewhere near
97 the beginning of 1970, details are complicated, don't ask). This type is
98 called <code>ev_tstamp</code>, which is what you should use too. It usually aliases
99 to the double type in C.</p>
102 <h1 id="GLOBAL_FUNCTIONS">GLOBAL FUNCTIONS</h1><p><a href="#TOP" class="toplink">Top</a></p>
103 <div id="GLOBAL_FUNCTIONS_CONTENT">
104 <p>These functions can be called anytime, even before initialising the
105 library in any way.</p>
107 <dt>ev_tstamp ev_time ()</dt>
109 <p>Returns the current time as libev would use it.</p>
111 <dt>int ev_version_major ()</dt>
112 <dt>int ev_version_minor ()</dt>
114 <p>You can find out the major and minor version numbers of the library
115 you linked against by calling the functions <code>ev_version_major</code> and
116 <code>ev_version_minor</code>. If you want, you can compare against the global
117 symbols <code>EV_VERSION_MAJOR</code> and <code>EV_VERSION_MINOR</code>, which specify the
118 version of the library your program was compiled against.</p>
119 <p>Usually, it's a good idea to terminate if the major versions mismatch,
120 as this indicates an incompatible change. Minor versions are usually
121 compatible to older versions, so a larger minor version alone is usually
124 <dt>ev_set_allocator (void *(*cb)(void *ptr, long size))</dt>
126 <p>Sets the allocation function to use (the prototype is similar to the
127 realloc C function, the semantics are identical). It is used to allocate
128 and free memory (no surprises here). If it returns zero when memory
129 needs to be allocated, the library might abort or take some potentially
130 destructive action. The default is your system realloc function.</p>
131 <p>You could override this function in high-availability programs to, say,
132 free some memory if it cannot allocate memory, to use a special allocator,
133 or even to sleep a while and retry until some memory is available.</p>
135 <dt>ev_set_syserr_cb (void (*cb)(const char *msg));</dt>
137 <p>Set the callback function to call on a retryable syscall error (such
138 as failed select, poll, epoll_wait). The message is a printable string
139 indicating the system call or subsystem causing the problem. If this
140 callback is set, then libev will expect it to remedy the sitution, no
141 matter what, when it returns. That is, libev will generally retry the
142 requested operation, or, if the condition doesn't go away, do bad stuff
148 <h1 id="FUNCTIONS_CONTROLLING_THE_EVENT_LOOP">FUNCTIONS CONTROLLING THE EVENT LOOP</h1><p><a href="#TOP" class="toplink">Top</a></p>
149 <div id="FUNCTIONS_CONTROLLING_THE_EVENT_LOOP-2">
150 <p>An event loop is described by a <code>struct ev_loop *</code>. The library knows two
151 types of such loops, the <i>default</i> loop, which supports signals and child
152 events, and dynamically created loops which do not.</p>
153 <p>If you use threads, a common model is to run the default event loop
154 in your main thread (or in a separate thread) and for each thread you
155 create, you also create another event loop. Libev itself does no locking
156 whatsoever, so if you mix calls to the same event loop in different
157 threads, make sure you lock (this is usually a bad idea, though, even if
158 done correctly, because it's hideous and inefficient).</p>
160 <dt>struct ev_loop *ev_default_loop (unsigned int flags)</dt>
162 <p>This will initialise the default event loop if it hasn't been initialised
163 yet and return it. If the default loop could not be initialised, returns
164 false. If it already was initialised it simply returns it (and ignores the
166 <p>If you don't know what event loop to use, use the one returned from this
168 <p>The flags argument can be used to specify special behaviour or specific
169 backends to use, and is usually specified as 0 (or EVFLAG_AUTO).</p>
170 <p>It supports the following flags:</p>
173 <dt><code>EVFLAG_AUTO</code></dt>
175 <p>The default flags value. Use this if you have no clue (it's the right
176 thing, believe me).</p>
178 <dt><code>EVFLAG_NOENV</code></dt>
180 <p>If this flag bit is ored into the flag value (or the program runs setuid
181 or setgid) then libev will <i>not</i> look at the environment variable
182 <code>LIBEV_FLAGS</code>. Otherwise (the default), this environment variable will
183 override the flags completely if it is found in the environment. This is
184 useful to try out specific backends to test their performance, or to work
187 <dt><code>EVMETHOD_SELECT</code> (portable select backend)</dt>
188 <dt><code>EVMETHOD_POLL</code> (poll backend, available everywhere except on windows)</dt>
189 <dt><code>EVMETHOD_EPOLL</code> (linux only)</dt>
190 <dt><code>EVMETHOD_KQUEUE</code> (some bsds only)</dt>
191 <dt><code>EVMETHOD_DEVPOLL</code> (solaris 8 only)</dt>
192 <dt><code>EVMETHOD_PORT</code> (solaris 10 only)</dt>
194 <p>If one or more of these are ored into the flags value, then only these
195 backends will be tried (in the reverse order as given here). If one are
196 specified, any backend will do.</p>
201 <dt>struct ev_loop *ev_loop_new (unsigned int flags)</dt>
203 <p>Similar to <code>ev_default_loop</code>, but always creates a new event loop that is
204 always distinct from the default loop. Unlike the default loop, it cannot
205 handle signal and child watchers, and attempts to do so will be greeted by
206 undefined behaviour (or a failed assertion if assertions are enabled).</p>
208 <dt>ev_default_destroy ()</dt>
210 <p>Destroys the default loop again (frees all memory and kernel state
211 etc.). This stops all registered event watchers (by not touching them in
212 any way whatsoever, although you cannot rely on this :).</p>
214 <dt>ev_loop_destroy (loop)</dt>
216 <p>Like <code>ev_default_destroy</code>, but destroys an event loop created by an
217 earlier call to <code>ev_loop_new</code>.</p>
219 <dt>ev_default_fork ()</dt>
221 <p>This function reinitialises the kernel state for backends that have
222 one. Despite the name, you can call it anytime, but it makes most sense
223 after forking, in either the parent or child process (or both, but that
224 again makes little sense).</p>
225 <p>You <i>must</i> call this function after forking if and only if you want to
226 use the event library in both processes. If you just fork+exec, you don't
228 <p>The function itself is quite fast and it's usually not a problem to call
229 it just in case after a fork. To make this easy, the function will fit in
230 quite nicely into a call to <code>pthread_atfork</code>:</p>
231 <pre> pthread_atfork (0, 0, ev_default_fork);
235 <dt>ev_loop_fork (loop)</dt>
237 <p>Like <code>ev_default_fork</code>, but acts on an event loop created by
238 <code>ev_loop_new</code>. Yes, you have to call this on every allocated event loop
239 after fork, and how you do this is entirely your own problem.</p>
241 <dt>unsigned int ev_method (loop)</dt>
243 <p>Returns one of the <code>EVMETHOD_*</code> flags indicating the event backend in
246 <dt>ev_tstamp ev_now (loop)</dt>
248 <p>Returns the current "event loop time", which is the time the event loop
249 got events and started processing them. This timestamp does not change
250 as long as callbacks are being processed, and this is also the base time
251 used for relative timers. You can treat it as the timestamp of the event
252 occuring (or more correctly, the mainloop finding out about it).</p>
254 <dt>ev_loop (loop, int flags)</dt>
256 <p>Finally, this is it, the event handler. This function usually is called
257 after you initialised all your watchers and you want to start handling
259 <p>If the flags argument is specified as 0, it will not return until either
260 no event watchers are active anymore or <code>ev_unloop</code> was called.</p>
261 <p>A flags value of <code>EVLOOP_NONBLOCK</code> will look for new events, will handle
262 those events and any outstanding ones, but will not block your process in
263 case there are no events and will return after one iteration of the loop.</p>
264 <p>A flags value of <code>EVLOOP_ONESHOT</code> will look for new events (waiting if
265 neccessary) and will handle those and any outstanding ones. It will block
266 your process until at least one new event arrives, and will return after
267 one iteration of the loop.</p>
268 <p>This flags value could be used to implement alternative looping
269 constructs, but the <code>prepare</code> and <code>check</code> watchers provide a better and
270 more generic mechanism.</p>
272 <dt>ev_unloop (loop, how)</dt>
274 <p>Can be used to make a call to <code>ev_loop</code> return early (but only after it
275 has processed all outstanding events). The <code>how</code> argument must be either
276 <code>EVUNLOOP_ONCE</code>, which will make the innermost <code>ev_loop</code> call return, or
277 <code>EVUNLOOP_ALL</code>, which will make all nested <code>ev_loop</code> calls return.</p>
279 <dt>ev_ref (loop)</dt>
280 <dt>ev_unref (loop)</dt>
282 <p>Ref/unref can be used to add or remove a reference count on the event
283 loop: Every watcher keeps one reference, and as long as the reference
284 count is nonzero, <code>ev_loop</code> will not return on its own. If you have
285 a watcher you never unregister that should not keep <code>ev_loop</code> from
286 returning, ev_unref() after starting, and ev_ref() before stopping it. For
287 example, libev itself uses this for its internal signal pipe: It is not
288 visible to the libev user and should not keep <code>ev_loop</code> from exiting if
289 no event watchers registered by it are active. It is also an excellent
290 way to do this for generic recurring timers or from within third-party
291 libraries. Just remember to <i>unref after start</i> and <i>ref before stop</i>.</p>
296 <h1 id="ANATOMY_OF_A_WATCHER">ANATOMY OF A WATCHER</h1><p><a href="#TOP" class="toplink">Top</a></p>
297 <div id="ANATOMY_OF_A_WATCHER_CONTENT">
298 <p>A watcher is a structure that you create and register to record your
299 interest in some event. For instance, if you want to wait for STDIN to
300 become readable, you would create an <code>ev_io</code> watcher for that:</p>
301 <pre> static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents)
304 ev_unloop (loop, EVUNLOOP_ALL);
307 struct ev_loop *loop = ev_default_loop (0);
308 struct ev_io stdin_watcher;
309 ev_init (&stdin_watcher, my_cb);
310 ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
311 ev_io_start (loop, &stdin_watcher);
315 <p>As you can see, you are responsible for allocating the memory for your
316 watcher structures (and it is usually a bad idea to do this on the stack,
317 although this can sometimes be quite valid).</p>
318 <p>Each watcher structure must be initialised by a call to <code>ev_init
319 (watcher *, callback)</code>, which expects a callback to be provided. This
320 callback gets invoked each time the event occurs (or, in the case of io
321 watchers, each time the event loop detects that the file descriptor given
322 is readable and/or writable).</p>
323 <p>Each watcher type has its own <code>ev_<type>_set (watcher *, ...)</code> macro
324 with arguments specific to this watcher type. There is also a macro
325 to combine initialisation and setting in one call: <code>ev_<type>_init
326 (watcher *, callback, ...)</code>.</p>
327 <p>To make the watcher actually watch out for events, you have to start it
328 with a watcher-specific start function (<code>ev_<type>_start (loop, watcher
329 *)</code>), and you can stop watching for events at any time by calling the
330 corresponding stop function (<code>ev_<type>_stop (loop, watcher *)</code>.</p>
331 <p>As long as your watcher is active (has been started but not stopped) you
332 must not touch the values stored in it. Most specifically you must never
333 reinitialise it or call its set method.</p>
334 <p>You can check whether an event is active by calling the <code>ev_is_active
335 (watcher *)</code> macro. To see whether an event is outstanding (but the
336 callback for it has not been called yet) you can use the <code>ev_is_pending
337 (watcher *)</code> macro.</p>
338 <p>Each and every callback receives the event loop pointer as first, the
339 registered watcher structure as second, and a bitset of received events as
341 <p>The received events usually include a single bit per event type received
342 (you can receive multiple events at the same time). The possible bit masks
345 <dt><code>EV_READ</code></dt>
346 <dt><code>EV_WRITE</code></dt>
348 <p>The file descriptor in the <code>ev_io</code> watcher has become readable and/or
351 <dt><code>EV_TIMEOUT</code></dt>
353 <p>The <code>ev_timer</code> watcher has timed out.</p>
355 <dt><code>EV_PERIODIC</code></dt>
357 <p>The <code>ev_periodic</code> watcher has timed out.</p>
359 <dt><code>EV_SIGNAL</code></dt>
361 <p>The signal specified in the <code>ev_signal</code> watcher has been received by a thread.</p>
363 <dt><code>EV_CHILD</code></dt>
365 <p>The pid specified in the <code>ev_child</code> watcher has received a status change.</p>
367 <dt><code>EV_IDLE</code></dt>
369 <p>The <code>ev_idle</code> watcher has determined that you have nothing better to do.</p>
371 <dt><code>EV_PREPARE</code></dt>
372 <dt><code>EV_CHECK</code></dt>
374 <p>All <code>ev_prepare</code> watchers are invoked just <i>before</i> <code>ev_loop</code> starts
375 to gather new events, and all <code>ev_check</code> watchers are invoked just after
376 <code>ev_loop</code> has gathered them, but before it invokes any callbacks for any
377 received events. Callbacks of both watcher types can start and stop as
378 many watchers as they want, and all of them will be taken into account
379 (for example, a <code>ev_prepare</code> watcher might start an idle watcher to keep
380 <code>ev_loop</code> from blocking).</p>
382 <dt><code>EV_ERROR</code></dt>
384 <p>An unspecified error has occured, the watcher has been stopped. This might
385 happen because the watcher could not be properly started because libev
386 ran out of memory, a file descriptor was found to be closed or any other
387 problem. You best act on it by reporting the problem and somehow coping
388 with the watcher being stopped.</p>
389 <p>Libev will usually signal a few "dummy" events together with an error,
390 for example it might indicate that a fd is readable or writable, and if
391 your callbacks is well-written it can just attempt the operation and cope
392 with the error from read() or write(). This will not work in multithreaded
393 programs, though, so beware.</p>
398 <h2 id="ASSOCIATING_CUSTOM_DATA_WITH_A_WATCH">ASSOCIATING CUSTOM DATA WITH A WATCHER</h2>
399 <div id="ASSOCIATING_CUSTOM_DATA_WITH_A_WATCH-2">
400 <p>Each watcher has, by default, a member <code>void *data</code> that you can change
401 and read at any time, libev will completely ignore it. This can be used
402 to associate arbitrary data with your watcher. If you need more data and
403 don't want to allocate memory and store a pointer to it in that data
404 member, you can also "subclass" the watcher type and provide your own
411 struct whatever *mostinteresting;
415 <p>And since your callback will be called with a pointer to the watcher, you
416 can cast it back to your own type:</p>
417 <pre> static void my_cb (struct ev_loop *loop, struct ev_io *w_, int revents)
419 struct my_io *w = (struct my_io *)w_;
424 <p>More interesting and less C-conformant ways of catsing your callback type
425 have been omitted....</p>
432 <h1 id="WATCHER_TYPES">WATCHER TYPES</h1><p><a href="#TOP" class="toplink">Top</a></p>
433 <div id="WATCHER_TYPES_CONTENT">
434 <p>This section describes each watcher in detail, but will not repeat
435 information given in the last section.</p>
438 <h2 id="code_ev_io_code_is_this_file_descrip"><code>ev_io</code> - is this file descriptor readable or writable</h2>
439 <div id="code_ev_io_code_is_this_file_descrip-2">
440 <p>I/O watchers check whether a file descriptor is readable or writable
441 in each iteration of the event loop (This behaviour is called
442 level-triggering because you keep receiving events as long as the
443 condition persists. Remember you can stop the watcher if you don't want to
444 act on the event and neither want to receive future events).</p>
445 <p>In general you can register as many read and/or write event watchers oer
446 fd as you want (as long as you don't confuse yourself). Setting all file
447 descriptors to non-blocking mode is also usually a good idea (but not
448 required if you know what you are doing).</p>
449 <p>You have to be careful with dup'ed file descriptors, though. Some backends
450 (the linux epoll backend is a notable example) cannot handle dup'ed file
451 descriptors correctly if you register interest in two or more fds pointing
452 to the same file/socket etc. description.</p>
453 <p>If you must do this, then force the use of a known-to-be-good backend
454 (at the time of this writing, this includes only EVMETHOD_SELECT and
457 <dt>ev_io_init (ev_io *, callback, int fd, int events)</dt>
458 <dt>ev_io_set (ev_io *, int fd, int events)</dt>
460 <p>Configures an <code>ev_io</code> watcher. The fd is the file descriptor to rceeive
461 events for and events is either <code>EV_READ</code>, <code>EV_WRITE</code> or <code>EV_READ |
462 EV_WRITE</code> to receive the given events.</p>
467 <h2 id="code_ev_timer_code_relative_and_opti"><code>ev_timer</code> - relative and optionally recurring timeouts</h2>
468 <div id="code_ev_timer_code_relative_and_opti-2">
469 <p>Timer watchers are simple relative timers that generate an event after a
470 given time, and optionally repeating in regular intervals after that.</p>
471 <p>The timers are based on real time, that is, if you register an event that
472 times out after an hour and youreset your system clock to last years
473 time, it will still time out after (roughly) and hour. "Roughly" because
474 detecting time jumps is hard, and soem inaccuracies are unavoidable (the
475 monotonic clock option helps a lot here).</p>
476 <p>The relative timeouts are calculated relative to the <code>ev_now ()</code>
477 time. This is usually the right thing as this timestamp refers to the time
478 of the event triggering whatever timeout you are modifying/starting. If
479 you suspect event processing to be delayed and you *need* to base the timeout
480 ion the current time, use something like this to adjust for this:</p>
481 <pre> ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);
485 <dt>ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)</dt>
486 <dt>ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)</dt>
488 <p>Configure the timer to trigger after <code>after</code> seconds. If <code>repeat</code> is
489 <code>0.</code>, then it will automatically be stopped. If it is positive, then the
490 timer will automatically be configured to trigger again <code>repeat</code> seconds
491 later, again, and again, until stopped manually.</p>
492 <p>The timer itself will do a best-effort at avoiding drift, that is, if you
493 configure a timer to trigger every 10 seconds, then it will trigger at
494 exactly 10 second intervals. If, however, your program cannot keep up with
495 the timer (ecause it takes longer than those 10 seconds to do stuff) the
496 timer will not fire more than once per event loop iteration.</p>
498 <dt>ev_timer_again (loop)</dt>
500 <p>This will act as if the timer timed out and restart it again if it is
501 repeating. The exact semantics are:</p>
502 <p>If the timer is started but nonrepeating, stop it.</p>
503 <p>If the timer is repeating, either start it if necessary (with the repeat
504 value), or reset the running timer to the repeat value.</p>
505 <p>This sounds a bit complicated, but here is a useful and typical
506 example: Imagine you have a tcp connection and you want a so-called idle
507 timeout, that is, you want to be called when there have been, say, 60
508 seconds of inactivity on the socket. The easiest way to do this is to
509 configure an <code>ev_timer</code> with after=repeat=60 and calling ev_timer_again each
510 time you successfully read or write some data. If you go into an idle
511 state where you do not expect data to travel on the socket, you can stop
512 the timer, and again will automatically restart it if need be.</p>
517 <h2 id="code_ev_periodic_code_to_cron_or_not"><code>ev_periodic</code> - to cron or not to cron</h2>
518 <div id="code_ev_periodic_code_to_cron_or_not-2">
519 <p>Periodic watchers are also timers of a kind, but they are very versatile
520 (and unfortunately a bit complex).</p>
521 <p>Unlike <code>ev_timer</code>'s, they are not based on real time (or relative time)
522 but on wallclock time (absolute time). You can tell a periodic watcher
523 to trigger "at" some specific point in time. For example, if you tell a
524 periodic watcher to trigger in 10 seconds (by specifiying e.g. c<ev_now ()
525 + 10.>) and then reset your system clock to the last year, then it will
526 take a year to trigger the event (unlike an <code>ev_timer</code>, which would trigger
527 roughly 10 seconds later and of course not if you reset your system time
529 <p>They can also be used to implement vastly more complex timers, such as
530 triggering an event on eahc midnight, local time.</p>
532 <dt>ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)</dt>
533 <dt>ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)</dt>
535 <p>Lots of arguments, lets sort it out... There are basically three modes of
536 operation, and we will explain them from simplest to complex:</p>
543 <dt>* absolute timer (interval = reschedule_cb = 0)</dt>
545 <p>In this configuration the watcher triggers an event at the wallclock time
546 <code>at</code> and doesn't repeat. It will not adjust when a time jump occurs,
547 that is, if it is to be run at January 1st 2011 then it will run when the
548 system time reaches or surpasses this time.</p>
550 <dt>* non-repeating interval timer (interval > 0, reschedule_cb = 0)</dt>
552 <p>In this mode the watcher will always be scheduled to time out at the next
553 <code>at + N * interval</code> time (for some integer N) and then repeat, regardless
554 of any time jumps.</p>
555 <p>This can be used to create timers that do not drift with respect to system
557 <pre> ev_periodic_set (&periodic, 0., 3600., 0);
560 <p>This doesn't mean there will always be 3600 seconds in between triggers,
561 but only that the the callback will be called when the system time shows a
562 full hour (UTC), or more correctly, when the system time is evenly divisible
564 <p>Another way to think about it (for the mathematically inclined) is that
565 <code>ev_periodic</code> will try to run the callback in this mode at the next possible
566 time where <code>time = at (mod interval)</code>, regardless of any time jumps.</p>
568 <dt>* manual reschedule mode (reschedule_cb = callback)</dt>
570 <p>In this mode the values for <code>interval</code> and <code>at</code> are both being
571 ignored. Instead, each time the periodic watcher gets scheduled, the
572 reschedule callback will be called with the watcher as first, and the
573 current time as second argument.</p>
574 <p>NOTE: <i>This callback MUST NOT stop or destroy any periodic watcher,
575 ever, or make any event loop modifications</i>. If you need to stop it,
576 return <code>now + 1e30</code> (or so, fudge fudge) and stop it afterwards (e.g. by
577 starting a prepare watcher).</p>
578 <p>Its prototype is <code>ev_tstamp (*reschedule_cb)(struct ev_periodic *w,
579 ev_tstamp now)</code>, e.g.:</p>
580 <pre> static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)
586 <p>It must return the next time to trigger, based on the passed time value
587 (that is, the lowest time value larger than to the second argument). It
588 will usually be called just before the callback will be triggered, but
589 might be called at other times, too.</p>
590 <p>NOTE: <i>This callback must always return a time that is later than the
591 passed <code>now</code> value</i>. Not even <code>now</code> itself will do, it must be larger.</p>
592 <p>This can be used to create very complex timers, such as a timer that
593 triggers on each midnight, local time. To do this, you would calculate the
594 next midnight after <code>now</code> and return the timestamp value for this. How you do this
595 is, again, up to you (but it is not trivial).</p>
600 <dt>ev_periodic_again (loop, ev_periodic *)</dt>
602 <p>Simply stops and restarts the periodic watcher again. This is only useful
603 when you changed some parameters or the reschedule callback would return
604 a different time than the last time it was called (e.g. in a crond like
605 program when the crontabs have changed).</p>
610 <h2 id="code_ev_signal_code_signal_me_when_a"><code>ev_signal</code> - signal me when a signal gets signalled</h2>
611 <div id="code_ev_signal_code_signal_me_when_a-2">
612 <p>Signal watchers will trigger an event when the process receives a specific
613 signal one or more times. Even though signals are very asynchronous, libev
614 will try it's best to deliver signals synchronously, i.e. as part of the
615 normal event processing, like any other event.</p>
616 <p>You can configure as many watchers as you like per signal. Only when the
617 first watcher gets started will libev actually register a signal watcher
618 with the kernel (thus it coexists with your own signal handlers as long
619 as you don't register any with libev). Similarly, when the last signal
620 watcher for a signal is stopped libev will reset the signal handler to
621 SIG_DFL (regardless of what it was set to before).</p>
623 <dt>ev_signal_init (ev_signal *, callback, int signum)</dt>
624 <dt>ev_signal_set (ev_signal *, int signum)</dt>
626 <p>Configures the watcher to trigger on the given signal number (usually one
627 of the <code>SIGxxx</code> constants).</p>
632 <h2 id="code_ev_child_code_wait_for_pid_stat"><code>ev_child</code> - wait for pid status changes</h2>
633 <div id="code_ev_child_code_wait_for_pid_stat-2">
634 <p>Child watchers trigger when your process receives a SIGCHLD in response to
635 some child status changes (most typically when a child of yours dies).</p>
637 <dt>ev_child_init (ev_child *, callback, int pid)</dt>
638 <dt>ev_child_set (ev_child *, int pid)</dt>
640 <p>Configures the watcher to wait for status changes of process <code>pid</code> (or
641 <i>any</i> process if <code>pid</code> is specified as <code>0</code>). The callback can look
642 at the <code>rstatus</code> member of the <code>ev_child</code> watcher structure to see
643 the status word (use the macros from <code>sys/wait.h</code> and see your systems
644 <code>waitpid</code> documentation). The <code>rpid</code> member contains the pid of the
645 process causing the status change.</p>
650 <h2 id="code_ev_idle_code_when_you_ve_got_no"><code>ev_idle</code> - when you've got nothing better to do</h2>
651 <div id="code_ev_idle_code_when_you_ve_got_no-2">
652 <p>Idle watchers trigger events when there are no other events are pending
653 (prepare, check and other idle watchers do not count). That is, as long
654 as your process is busy handling sockets or timeouts (or even signals,
655 imagine) it will not be triggered. But when your process is idle all idle
656 watchers are being called again and again, once per event loop iteration -
657 until stopped, that is, or your process receives more events and becomes
659 <p>The most noteworthy effect is that as long as any idle watchers are
660 active, the process will not block when waiting for new events.</p>
661 <p>Apart from keeping your process non-blocking (which is a useful
662 effect on its own sometimes), idle watchers are a good place to do
663 "pseudo-background processing", or delay processing stuff to after the
664 event loop has handled all outstanding events.</p>
666 <dt>ev_idle_init (ev_signal *, callback)</dt>
668 <p>Initialises and configures the idle watcher - it has no parameters of any
669 kind. There is a <code>ev_idle_set</code> macro, but using it is utterly pointless,
675 <h2 id="code_ev_prepare_code_and_code_ev_che"><code>ev_prepare</code> and <code>ev_check</code> - customise your event loop</h2>
676 <div id="code_ev_prepare_code_and_code_ev_che-2">
677 <p>Prepare and check watchers are usually (but not always) used in tandem:
678 Prepare watchers get invoked before the process blocks and check watchers
680 <p>Their main purpose is to integrate other event mechanisms into libev. This
681 could be used, for example, to track variable changes, implement your own
682 watchers, integrate net-snmp or a coroutine library and lots more.</p>
683 <p>This is done by examining in each prepare call which file descriptors need
684 to be watched by the other library, registering <code>ev_io</code> watchers for
685 them and starting an <code>ev_timer</code> watcher for any timeouts (many libraries
686 provide just this functionality). Then, in the check watcher you check for
687 any events that occured (by checking the pending status of all watchers
688 and stopping them) and call back into the library. The I/O and timer
689 callbacks will never actually be called (but must be valid neverthelles,
690 because you never know, you know?).</p>
691 <p>As another example, the Perl Coro module uses these hooks to integrate
692 coroutines into libev programs, by yielding to other active coroutines
693 during each prepare and only letting the process block if no coroutines
694 are ready to run (its actually more complicated, it only runs coroutines
695 with priority higher than the event loop and one lower priority once,
696 using idle watchers to keep the event loop from blocking if lower-priority
697 coroutines exist, thus mapping low-priority coroutines to idle/background
700 <dt>ev_prepare_init (ev_prepare *, callback)</dt>
701 <dt>ev_check_init (ev_check *, callback)</dt>
703 <p>Initialises and configures the prepare or check watcher - they have no
704 parameters of any kind. There are <code>ev_prepare_set</code> and <code>ev_check_set</code>
705 macros, but using them is utterly, utterly and completely pointless.</p>
710 <h1 id="OTHER_FUNCTIONS">OTHER FUNCTIONS</h1><p><a href="#TOP" class="toplink">Top</a></p>
711 <div id="OTHER_FUNCTIONS_CONTENT">
712 <p>There are some other functions of possible interest. Described. Here. Now.</p>
714 <dt>ev_once (loop, int fd, int events, ev_tstamp timeout, callback)</dt>
716 <p>This function combines a simple timer and an I/O watcher, calls your
717 callback on whichever event happens first and automatically stop both
718 watchers. This is useful if you want to wait for a single event on an fd
719 or timeout without havign to allocate/configure/start/stop/free one or
720 more watchers yourself.</p>
721 <p>If <code>fd</code> is less than 0, then no I/O watcher will be started and events
722 is being ignored. Otherwise, an <code>ev_io</code> watcher for the given <code>fd</code> and
723 <code>events</code> set will be craeted and started.</p>
724 <p>If <code>timeout</code> is less than 0, then no timeout watcher will be
725 started. Otherwise an <code>ev_timer</code> watcher with after = <code>timeout</code> (and
726 repeat = 0) will be started. While <code>0</code> is a valid timeout, it is of
728 <p>The callback has the type <code>void (*cb)(int revents, void *arg)</code> and gets
729 passed an events set like normal event callbacks (with a combination of
730 <code>EV_ERROR</code>, <code>EV_READ</code>, <code>EV_WRITE</code> or <code>EV_TIMEOUT</code>) and the <code>arg</code>
731 value passed to <code>ev_once</code>:</p>
732 <pre> static void stdin_ready (int revents, void *arg)
734 if (revents & EV_TIMEOUT)
735 /* doh, nothing entered */;
736 else if (revents & EV_READ)
737 /* stdin might have data for us, joy! */;
740 ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
744 <dt>ev_feed_event (loop, watcher, int events)</dt>
746 <p>Feeds the given event set into the event loop, as if the specified event
747 had happened for the specified watcher (which must be a pointer to an
748 initialised but not necessarily started event watcher).</p>
750 <dt>ev_feed_fd_event (loop, int fd, int revents)</dt>
752 <p>Feed an event on the given fd, as if a file descriptor backend detected
753 the given events it.</p>
755 <dt>ev_feed_signal_event (loop, int signum)</dt>
757 <p>Feed an event as if the given signal occured (loop must be the default loop!).</p>
762 <h1 id="AUTHOR">AUTHOR</h1><p><a href="#TOP" class="toplink">Top</a></p>
763 <div id="AUTHOR_CONTENT">
764 <p>Marc Lehmann <libev@schmorp.de>.</p>
projects / software / libev.git / blob