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1 <?xml version="1.0" encoding="UTF-8"?>
2 <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.1//EN" "">
3 <html xmlns="" xml:lang="en">
4 <head>
5 <title>libev</title>
6 <meta name="description" content="Pod documentation for libev" />
7 <meta name="inputfile" content="&lt;standard input&gt;" />
8 <meta name="outputfile" content="&lt;standard output&gt;" />
9 <meta name="created" content="Wed Dec 12 18:55:28 2007" />
10 <meta name="generator" content="Pod::Xhtml 1.57" />
11 <link rel="stylesheet" href=""/></head>
12 <body>
13 <div class="pod">
14 <!-- INDEX START -->
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="#EXAMPLE_PROGRAM">EXAMPLE PROGRAM</a></li>
20 <li><a href="#DESCRIPTION">DESCRIPTION</a></li>
21 <li><a href="#FEATURES">FEATURES</a></li>
22 <li><a href="#CONVENTIONS">CONVENTIONS</a></li>
24 <li><a href="#GLOBAL_FUNCTIONS">GLOBAL FUNCTIONS</a></li>
29 </ul>
30 </li>
31 <li><a href="#WATCHER_TYPES">WATCHER TYPES</a>
32 <ul><li><a href="#code_ev_io_code_is_this_file_descrip"><code>ev_io</code> - is this file descriptor readable or writable?</a>
33 <ul><li><a href="#The_special_problem_of_disappearing_">The special problem of disappearing file descriptors</a></li>
34 <li><a href="#Watcher_Specific_Functions">Watcher-Specific Functions</a></li>
35 </ul>
36 </li>
37 <li><a href="#code_ev_timer_code_relative_and_opti"><code>ev_timer</code> - relative and optionally repeating timeouts</a>
38 <ul><li><a href="#Watcher_Specific_Functions_and_Data_">Watcher-Specific Functions and Data Members</a></li>
39 </ul>
40 </li>
41 <li><a href="#code_ev_periodic_code_to_cron_or_not"><code>ev_periodic</code> - to cron or not to cron?</a>
42 <ul><li><a href="#Watcher_Specific_Functions_and_Data_-3">Watcher-Specific Functions and Data Members</a></li>
43 </ul>
44 </li>
45 <li><a href="#code_ev_signal_code_signal_me_when_a"><code>ev_signal</code> - signal me when a signal gets signalled!</a>
46 <ul><li><a href="#Watcher_Specific_Functions_and_Data_-4">Watcher-Specific Functions and Data Members</a></li>
47 </ul>
48 </li>
49 <li><a href="#code_ev_child_code_watch_out_for_pro"><code>ev_child</code> - watch out for process status changes</a>
50 <ul><li><a href="#Watcher_Specific_Functions_and_Data_-5">Watcher-Specific Functions and Data Members</a></li>
51 </ul>
52 </li>
53 <li><a href="#code_ev_stat_code_did_the_file_attri"><code>ev_stat</code> - did the file attributes just change?</a>
54 <ul><li><a href="#Watcher_Specific_Functions_and_Data_-6">Watcher-Specific Functions and Data Members</a></li>
55 </ul>
56 </li>
57 <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>
58 <ul><li><a href="#Watcher_Specific_Functions_and_Data_-7">Watcher-Specific Functions and Data Members</a></li>
59 </ul>
60 </li>
61 <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>
62 <ul><li><a href="#Watcher_Specific_Functions_and_Data_-8">Watcher-Specific Functions and Data Members</a></li>
63 </ul>
64 </li>
65 <li><a href="#code_ev_embed_code_when_one_backend_"><code>ev_embed</code> - when one backend isn't enough...</a>
66 <ul><li><a href="#Watcher_Specific_Functions_and_Data_-9">Watcher-Specific Functions and Data Members</a></li>
67 </ul>
68 </li>
69 <li><a href="#code_ev_fork_code_the_audacity_to_re"><code>ev_fork</code> - the audacity to resume the event loop after a fork</a>
70 <ul><li><a href="#Watcher_Specific_Functions_and_Data_-10">Watcher-Specific Functions and Data Members</a></li>
71 </ul>
72 </li>
73 </ul>
74 </li>
75 <li><a href="#OTHER_FUNCTIONS">OTHER FUNCTIONS</a></li>
77 <li><a href="#C_SUPPORT">C++ SUPPORT</a></li>
78 <li><a href="#MACRO_MAGIC">MACRO MAGIC</a></li>
79 <li><a href="#EMBEDDING">EMBEDDING</a>
80 <ul><li><a href="#FILESETS">FILESETS</a>
81 <ul><li><a href="#CORE_EVENT_LOOP">CORE EVENT LOOP</a></li>
83 <li><a href="#AUTOCONF_SUPPORT">AUTOCONF SUPPORT</a></li>
84 </ul>
85 </li>
87 <li><a href="#EXAMPLES">EXAMPLES</a></li>
88 </ul>
89 </li>
90 <li><a href="#COMPLEXITIES">COMPLEXITIES</a></li>
91 <li><a href="#AUTHOR">AUTHOR</a>
92 </li>
93 </ul><hr />
94 <!-- INDEX END -->
96 <h1 id="NAME">NAME</h1>
97 <div id="NAME_CONTENT">
98 <p>libev - a high performance full-featured event loop written in C</p>
100 </div>
101 <h1 id="SYNOPSIS">SYNOPSIS</h1>
102 <div id="SYNOPSIS_CONTENT">
103 <pre> #include &lt;ev.h&gt;
105 </pre>
107 </div>
110 <pre> #include &lt;ev.h&gt;
112 ev_io stdin_watcher;
113 ev_timer timeout_watcher;
115 /* called when data readable on stdin */
116 static void
117 stdin_cb (EV_P_ struct ev_io *w, int revents)
118 {
119 /* puts (&quot;stdin ready&quot;); */
120 ev_io_stop (EV_A_ w); /* just a syntax example */
121 ev_unloop (EV_A_ EVUNLOOP_ALL); /* leave all loop calls */
122 }
124 static void
125 timeout_cb (EV_P_ struct ev_timer *w, int revents)
126 {
127 /* puts (&quot;timeout&quot;); */
128 ev_unloop (EV_A_ EVUNLOOP_ONE); /* leave one loop call */
129 }
131 int
132 main (void)
133 {
134 struct ev_loop *loop = ev_default_loop (0);
136 /* initialise an io watcher, then start it */
137 ev_io_init (&amp;stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ);
138 ev_io_start (loop, &amp;stdin_watcher);
140 /* simple non-repeating 5.5 second timeout */
141 ev_timer_init (&amp;timeout_watcher, timeout_cb, 5.5, 0.);
142 ev_timer_start (loop, &amp;timeout_watcher);
144 /* loop till timeout or data ready */
145 ev_loop (loop, 0);
147 return 0;
148 }
150 </pre>
152 </div>
155 <p>The newest version of this document is also available as a html-formatted
156 web page you might find easier to navigate when reading it for the first
157 time: <a href=""></a>.</p>
158 <p>Libev is an event loop: you register interest in certain events (such as a
159 file descriptor being readable or a timeout occuring), and it will manage
160 these event sources and provide your program with events.</p>
161 <p>To do this, it must take more or less complete control over your process
162 (or thread) by executing the <i>event loop</i> handler, and will then
163 communicate events via a callback mechanism.</p>
164 <p>You register interest in certain events by registering so-called <i>event
165 watchers</i>, which are relatively small C structures you initialise with the
166 details of the event, and then hand it over to libev by <i>starting</i> the
167 watcher.</p>
169 </div>
170 <h1 id="FEATURES">FEATURES</h1>
171 <div id="FEATURES_CONTENT">
172 <p>Libev supports <code>select</code>, <code>poll</code>, the Linux-specific <code>epoll</code>, the
173 BSD-specific <code>kqueue</code> and the Solaris-specific event port mechanisms
174 for file descriptor events (<code>ev_io</code>), the Linux <code>inotify</code> interface
175 (for <code>ev_stat</code>), relative timers (<code>ev_timer</code>), absolute timers
176 with customised rescheduling (<code>ev_periodic</code>), synchronous signals
177 (<code>ev_signal</code>), process status change events (<code>ev_child</code>), and event
178 watchers dealing with the event loop mechanism itself (<code>ev_idle</code>,
179 <code>ev_embed</code>, <code>ev_prepare</code> and <code>ev_check</code> watchers) as well as
180 file watchers (<code>ev_stat</code>) and even limited support for fork events
181 (<code>ev_fork</code>).</p>
182 <p>It also is quite fast (see this
183 <a href="">benchmark</a> comparing it to libevent
184 for example).</p>
186 </div>
189 <p>Libev is very configurable. In this manual the default configuration will
190 be described, which supports multiple event loops. For more info about
191 various configuration options please have a look at <strong>EMBED</strong> section in
192 this manual. If libev was configured without support for multiple event
193 loops, then all functions taking an initial argument of name <code>loop</code>
194 (which is always of type <code>struct ev_loop *</code>) will not have this argument.</p>
196 </div>
199 <p>Libev represents time as a single floating point number, representing the
200 (fractional) number of seconds since the (POSIX) epoch (somewhere near
201 the beginning of 1970, details are complicated, don't ask). This type is
202 called <code>ev_tstamp</code>, which is what you should use too. It usually aliases
203 to the <code>double</code> type in C, and when you need to do any calculations on
204 it, you should treat it as such.</p>
206 </div>
209 <p>These functions can be called anytime, even before initialising the
210 library in any way.</p>
211 <dl>
212 <dt>ev_tstamp ev_time ()</dt>
213 <dd>
214 <p>Returns the current time as libev would use it. Please note that the
215 <code>ev_now</code> function is usually faster and also often returns the timestamp
216 you actually want to know.</p>
217 </dd>
218 <dt>int ev_version_major ()</dt>
219 <dt>int ev_version_minor ()</dt>
220 <dd>
221 <p>You can find out the major and minor ABI version numbers of the library
222 you linked against by calling the functions <code>ev_version_major</code> and
223 <code>ev_version_minor</code>. If you want, you can compare against the global
224 symbols <code>EV_VERSION_MAJOR</code> and <code>EV_VERSION_MINOR</code>, which specify the
225 version of the library your program was compiled against.</p>
226 <p>These version numbers refer to the ABI version of the library, not the
227 release version.</p>
228 <p>Usually, it's a good idea to terminate if the major versions mismatch,
229 as this indicates an incompatible change. Minor versions are usually
230 compatible to older versions, so a larger minor version alone is usually
231 not a problem.</p>
232 <p>Example: Make sure we haven't accidentally been linked against the wrong
233 version.</p>
234 <pre> assert ((&quot;libev version mismatch&quot;,
235 ev_version_major () == EV_VERSION_MAJOR
236 &amp;&amp; ev_version_minor () &gt;= EV_VERSION_MINOR));
238 </pre>
239 </dd>
240 <dt>unsigned int ev_supported_backends ()</dt>
241 <dd>
242 <p>Return the set of all backends (i.e. their corresponding <code>EV_BACKEND_*</code>
243 value) compiled into this binary of libev (independent of their
244 availability on the system you are running on). See <code>ev_default_loop</code> for
245 a description of the set values.</p>
246 <p>Example: make sure we have the epoll method, because yeah this is cool and
247 a must have and can we have a torrent of it please!!!11</p>
248 <pre> assert ((&quot;sorry, no epoll, no sex&quot;,
249 ev_supported_backends () &amp; EVBACKEND_EPOLL));
251 </pre>
252 </dd>
253 <dt>unsigned int ev_recommended_backends ()</dt>
254 <dd>
255 <p>Return the set of all backends compiled into this binary of libev and also
256 recommended for this platform. This set is often smaller than the one
257 returned by <code>ev_supported_backends</code>, as for example kqueue is broken on
258 most BSDs and will not be autodetected unless you explicitly request it
259 (assuming you know what you are doing). This is the set of backends that
260 libev will probe for if you specify no backends explicitly.</p>
261 </dd>
262 <dt>unsigned int ev_embeddable_backends ()</dt>
263 <dd>
264 <p>Returns the set of backends that are embeddable in other event loops. This
265 is the theoretical, all-platform, value. To find which backends
266 might be supported on the current system, you would need to look at
267 <code>ev_embeddable_backends () &amp; ev_supported_backends ()</code>, likewise for
268 recommended ones.</p>
269 <p>See the description of <code>ev_embed</code> watchers for more info.</p>
270 </dd>
271 <dt>ev_set_allocator (void *(*cb)(void *ptr, long size))</dt>
272 <dd>
273 <p>Sets the allocation function to use (the prototype is similar - the
274 semantics is identical - to the realloc C function). It is used to
275 allocate and free memory (no surprises here). If it returns zero when
276 memory needs to be allocated, the library might abort or take some
277 potentially destructive action. The default is your system realloc
278 function.</p>
279 <p>You could override this function in high-availability programs to, say,
280 free some memory if it cannot allocate memory, to use a special allocator,
281 or even to sleep a while and retry until some memory is available.</p>
282 <p>Example: Replace the libev allocator with one that waits a bit and then
283 retries).</p>
284 <pre> static void *
285 persistent_realloc (void *ptr, size_t size)
286 {
287 for (;;)
288 {
289 void *newptr = realloc (ptr, size);
291 if (newptr)
292 return newptr;
294 sleep (60);
295 }
296 }
298 ...
299 ev_set_allocator (persistent_realloc);
301 </pre>
302 </dd>
303 <dt>ev_set_syserr_cb (void (*cb)(const char *msg));</dt>
304 <dd>
305 <p>Set the callback function to call on a retryable syscall error (such
306 as failed select, poll, epoll_wait). The message is a printable string
307 indicating the system call or subsystem causing the problem. If this
308 callback is set, then libev will expect it to remedy the sitution, no
309 matter what, when it returns. That is, libev will generally retry the
310 requested operation, or, if the condition doesn't go away, do bad stuff
311 (such as abort).</p>
312 <p>Example: This is basically the same thing that libev does internally, too.</p>
313 <pre> static void
314 fatal_error (const char *msg)
315 {
316 perror (msg);
317 abort ();
318 }
320 ...
321 ev_set_syserr_cb (fatal_error);
323 </pre>
324 </dd>
325 </dl>
327 </div>
330 <p>An event loop is described by a <code>struct ev_loop *</code>. The library knows two
331 types of such loops, the <i>default</i> loop, which supports signals and child
332 events, and dynamically created loops which do not.</p>
333 <p>If you use threads, a common model is to run the default event loop
334 in your main thread (or in a separate thread) and for each thread you
335 create, you also create another event loop. Libev itself does no locking
336 whatsoever, so if you mix calls to the same event loop in different
337 threads, make sure you lock (this is usually a bad idea, though, even if
338 done correctly, because it's hideous and inefficient).</p>
339 <dl>
340 <dt>struct ev_loop *ev_default_loop (unsigned int flags)</dt>
341 <dd>
342 <p>This will initialise the default event loop if it hasn't been initialised
343 yet and return it. If the default loop could not be initialised, returns
344 false. If it already was initialised it simply returns it (and ignores the
345 flags. If that is troubling you, check <code>ev_backend ()</code> afterwards).</p>
346 <p>If you don't know what event loop to use, use the one returned from this
347 function.</p>
348 <p>The flags argument can be used to specify special behaviour or specific
349 backends to use, and is usually specified as <code>0</code> (or <code>EVFLAG_AUTO</code>).</p>
350 <p>The following flags are supported:</p>
351 <p>
352 <dl>
353 <dt><code>EVFLAG_AUTO</code></dt>
354 <dd>
355 <p>The default flags value. Use this if you have no clue (it's the right
356 thing, believe me).</p>
357 </dd>
358 <dt><code>EVFLAG_NOENV</code></dt>
359 <dd>
360 <p>If this flag bit is ored into the flag value (or the program runs setuid
361 or setgid) then libev will <i>not</i> look at the environment variable
362 <code>LIBEV_FLAGS</code>. Otherwise (the default), this environment variable will
363 override the flags completely if it is found in the environment. This is
364 useful to try out specific backends to test their performance, or to work
365 around bugs.</p>
366 </dd>
367 <dt><code>EVFLAG_FORKCHECK</code></dt>
368 <dd>
369 <p>Instead of calling <code>ev_default_fork</code> or <code>ev_loop_fork</code> manually after
370 a fork, you can also make libev check for a fork in each iteration by
371 enabling this flag.</p>
372 <p>This works by calling <code>getpid ()</code> on every iteration of the loop,
373 and thus this might slow down your event loop if you do a lot of loop
374 iterations and little real work, but is usually not noticeable (on my
375 Linux system for example, <code>getpid</code> is actually a simple 5-insn sequence
376 without a syscall and thus <i>very</i> fast, but my Linux system also has
377 <code>pthread_atfork</code> which is even faster).</p>
378 <p>The big advantage of this flag is that you can forget about fork (and
379 forget about forgetting to tell libev about forking) when you use this
380 flag.</p>
381 <p>This flag setting cannot be overriden or specified in the <code>LIBEV_FLAGS</code>
382 environment variable.</p>
383 </dd>
384 <dt><code>EVBACKEND_SELECT</code> (value 1, portable select backend)</dt>
385 <dd>
386 <p>This is your standard select(2) backend. Not <i>completely</i> standard, as
387 libev tries to roll its own fd_set with no limits on the number of fds,
388 but if that fails, expect a fairly low limit on the number of fds when
389 using this backend. It doesn't scale too well (O(highest_fd)), but its usually
390 the fastest backend for a low number of fds.</p>
391 </dd>
392 <dt><code>EVBACKEND_POLL</code> (value 2, poll backend, available everywhere except on windows)</dt>
393 <dd>
394 <p>And this is your standard poll(2) backend. It's more complicated than
395 select, but handles sparse fds better and has no artificial limit on the
396 number of fds you can use (except it will slow down considerably with a
397 lot of inactive fds). It scales similarly to select, i.e. O(total_fds).</p>
398 </dd>
399 <dt><code>EVBACKEND_EPOLL</code> (value 4, Linux)</dt>
400 <dd>
401 <p>For few fds, this backend is a bit little slower than poll and select,
402 but it scales phenomenally better. While poll and select usually scale like
403 O(total_fds) where n is the total number of fds (or the highest fd), epoll scales
404 either O(1) or O(active_fds).</p>
405 <p>While stopping and starting an I/O watcher in the same iteration will
406 result in some caching, there is still a syscall per such incident
407 (because the fd could point to a different file description now), so its
408 best to avoid that. Also, dup()ed file descriptors might not work very
409 well if you register events for both fds.</p>
410 <p>Please note that epoll sometimes generates spurious notifications, so you
411 need to use non-blocking I/O or other means to avoid blocking when no data
412 (or space) is available.</p>
413 </dd>
414 <dt><code>EVBACKEND_KQUEUE</code> (value 8, most BSD clones)</dt>
415 <dd>
416 <p>Kqueue deserves special mention, as at the time of this writing, it
417 was broken on all BSDs except NetBSD (usually it doesn't work with
418 anything but sockets and pipes, except on Darwin, where of course its
419 completely useless). For this reason its not being &quot;autodetected&quot;
420 unless you explicitly specify it explicitly in the flags (i.e. using
421 <code>EVBACKEND_KQUEUE</code>).</p>
422 <p>It scales in the same way as the epoll backend, but the interface to the
423 kernel is more efficient (which says nothing about its actual speed, of
424 course). While starting and stopping an I/O watcher does not cause an
425 extra syscall as with epoll, it still adds up to four event changes per
426 incident, so its best to avoid that.</p>
427 </dd>
428 <dt><code>EVBACKEND_DEVPOLL</code> (value 16, Solaris 8)</dt>
429 <dd>
430 <p>This is not implemented yet (and might never be).</p>
431 </dd>
432 <dt><code>EVBACKEND_PORT</code> (value 32, Solaris 10)</dt>
433 <dd>
434 <p>This uses the Solaris 10 port mechanism. As with everything on Solaris,
435 it's really slow, but it still scales very well (O(active_fds)).</p>
436 <p>Please note that solaris ports can result in a lot of spurious
437 notifications, so you need to use non-blocking I/O or other means to avoid
438 blocking when no data (or space) is available.</p>
439 </dd>
440 <dt><code>EVBACKEND_ALL</code></dt>
441 <dd>
442 <p>Try all backends (even potentially broken ones that wouldn't be tried
443 with <code>EVFLAG_AUTO</code>). Since this is a mask, you can do stuff such as
444 <code>EVBACKEND_ALL &amp; ~EVBACKEND_KQUEUE</code>.</p>
445 </dd>
446 </dl>
447 </p>
448 <p>If one or more of these are ored into the flags value, then only these
449 backends will be tried (in the reverse order as given here). If none are
450 specified, most compiled-in backend will be tried, usually in reverse
451 order of their flag values :)</p>
452 <p>The most typical usage is like this:</p>
453 <pre> if (!ev_default_loop (0))
454 fatal (&quot;could not initialise libev, bad $LIBEV_FLAGS in environment?&quot;);
456 </pre>
457 <p>Restrict libev to the select and poll backends, and do not allow
458 environment settings to be taken into account:</p>
461 </pre>
462 <p>Use whatever libev has to offer, but make sure that kqueue is used if
463 available (warning, breaks stuff, best use only with your own private
464 event loop and only if you know the OS supports your types of fds):</p>
465 <pre> ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);
467 </pre>
468 </dd>
469 <dt>struct ev_loop *ev_loop_new (unsigned int flags)</dt>
470 <dd>
471 <p>Similar to <code>ev_default_loop</code>, but always creates a new event loop that is
472 always distinct from the default loop. Unlike the default loop, it cannot
473 handle signal and child watchers, and attempts to do so will be greeted by
474 undefined behaviour (or a failed assertion if assertions are enabled).</p>
475 <p>Example: Try to create a event loop that uses epoll and nothing else.</p>
476 <pre> struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
477 if (!epoller)
478 fatal (&quot;no epoll found here, maybe it hides under your chair&quot;);
480 </pre>
481 </dd>
482 <dt>ev_default_destroy ()</dt>
483 <dd>
484 <p>Destroys the default loop again (frees all memory and kernel state
485 etc.). None of the active event watchers will be stopped in the normal
486 sense, so e.g. <code>ev_is_active</code> might still return true. It is your
487 responsibility to either stop all watchers cleanly yoursef <i>before</i>
488 calling this function, or cope with the fact afterwards (which is usually
489 the easiest thing, youc na just ignore the watchers and/or <code>free ()</code> them
490 for example).</p>
491 </dd>
492 <dt>ev_loop_destroy (loop)</dt>
493 <dd>
494 <p>Like <code>ev_default_destroy</code>, but destroys an event loop created by an
495 earlier call to <code>ev_loop_new</code>.</p>
496 </dd>
497 <dt>ev_default_fork ()</dt>
498 <dd>
499 <p>This function reinitialises the kernel state for backends that have
500 one. Despite the name, you can call it anytime, but it makes most sense
501 after forking, in either the parent or child process (or both, but that
502 again makes little sense).</p>
503 <p>You <i>must</i> call this function in the child process after forking if and
504 only if you want to use the event library in both processes. If you just
505 fork+exec, you don't have to call it.</p>
506 <p>The function itself is quite fast and it's usually not a problem to call
507 it just in case after a fork. To make this easy, the function will fit in
508 quite nicely into a call to <code>pthread_atfork</code>:</p>
509 <pre> pthread_atfork (0, 0, ev_default_fork);
511 </pre>
512 <p>At the moment, <code>EVBACKEND_SELECT</code> and <code>EVBACKEND_POLL</code> are safe to use
513 without calling this function, so if you force one of those backends you
514 do not need to care.</p>
515 </dd>
516 <dt>ev_loop_fork (loop)</dt>
517 <dd>
518 <p>Like <code>ev_default_fork</code>, but acts on an event loop created by
519 <code>ev_loop_new</code>. Yes, you have to call this on every allocated event loop
520 after fork, and how you do this is entirely your own problem.</p>
521 </dd>
522 <dt>unsigned int ev_loop_count (loop)</dt>
523 <dd>
524 <p>Returns the count of loop iterations for the loop, which is identical to
525 the number of times libev did poll for new events. It starts at <code>0</code> and
526 happily wraps around with enough iterations.</p>
527 <p>This value can sometimes be useful as a generation counter of sorts (it
528 &quot;ticks&quot; the number of loop iterations), as it roughly corresponds with
529 <code>ev_prepare</code> and <code>ev_check</code> calls.</p>
530 </dd>
531 <dt>unsigned int ev_backend (loop)</dt>
532 <dd>
533 <p>Returns one of the <code>EVBACKEND_*</code> flags indicating the event backend in
534 use.</p>
535 </dd>
536 <dt>ev_tstamp ev_now (loop)</dt>
537 <dd>
538 <p>Returns the current &quot;event loop time&quot;, which is the time the event loop
539 received events and started processing them. This timestamp does not
540 change as long as callbacks are being processed, and this is also the base
541 time used for relative timers. You can treat it as the timestamp of the
542 event occuring (or more correctly, libev finding out about it).</p>
543 </dd>
544 <dt>ev_loop (loop, int flags)</dt>
545 <dd>
546 <p>Finally, this is it, the event handler. This function usually is called
547 after you initialised all your watchers and you want to start handling
548 events.</p>
549 <p>If the flags argument is specified as <code>0</code>, it will not return until
550 either no event watchers are active anymore or <code>ev_unloop</code> was called.</p>
551 <p>Please note that an explicit <code>ev_unloop</code> is usually better than
552 relying on all watchers to be stopped when deciding when a program has
553 finished (especially in interactive programs), but having a program that
554 automatically loops as long as it has to and no longer by virtue of
555 relying on its watchers stopping correctly is a thing of beauty.</p>
556 <p>A flags value of <code>EVLOOP_NONBLOCK</code> will look for new events, will handle
557 those events and any outstanding ones, but will not block your process in
558 case there are no events and will return after one iteration of the loop.</p>
559 <p>A flags value of <code>EVLOOP_ONESHOT</code> will look for new events (waiting if
560 neccessary) and will handle those and any outstanding ones. It will block
561 your process until at least one new event arrives, and will return after
562 one iteration of the loop. This is useful if you are waiting for some
563 external event in conjunction with something not expressible using other
564 libev watchers. However, a pair of <code>ev_prepare</code>/<code>ev_check</code> watchers is
565 usually a better approach for this kind of thing.</p>
566 <p>Here are the gory details of what <code>ev_loop</code> does:</p>
567 <pre> - Before the first iteration, call any pending watchers.
568 * If there are no active watchers (reference count is zero), return.
569 - Queue all prepare watchers and then call all outstanding watchers.
570 - If we have been forked, recreate the kernel state.
571 - Update the kernel state with all outstanding changes.
572 - Update the &quot;event loop time&quot;.
573 - Calculate for how long to block.
574 - Block the process, waiting for any events.
575 - Queue all outstanding I/O (fd) events.
576 - Update the &quot;event loop time&quot; and do time jump handling.
577 - Queue all outstanding timers.
578 - Queue all outstanding periodics.
579 - If no events are pending now, queue all idle watchers.
580 - Queue all check watchers.
581 - Call all queued watchers in reverse order (i.e. check watchers first).
582 Signals and child watchers are implemented as I/O watchers, and will
583 be handled here by queueing them when their watcher gets executed.
584 - If ev_unloop has been called or EVLOOP_ONESHOT or EVLOOP_NONBLOCK
585 were used, return, otherwise continue with step *.
587 </pre>
588 <p>Example: Queue some jobs and then loop until no events are outsanding
589 anymore.</p>
590 <pre> ... queue jobs here, make sure they register event watchers as long
591 ... as they still have work to do (even an idle watcher will do..)
592 ev_loop (my_loop, 0);
593 ... jobs done. yeah!
595 </pre>
596 </dd>
597 <dt>ev_unloop (loop, how)</dt>
598 <dd>
599 <p>Can be used to make a call to <code>ev_loop</code> return early (but only after it
600 has processed all outstanding events). The <code>how</code> argument must be either
601 <code>EVUNLOOP_ONE</code>, which will make the innermost <code>ev_loop</code> call return, or
602 <code>EVUNLOOP_ALL</code>, which will make all nested <code>ev_loop</code> calls return.</p>
603 </dd>
604 <dt>ev_ref (loop)</dt>
605 <dt>ev_unref (loop)</dt>
606 <dd>
607 <p>Ref/unref can be used to add or remove a reference count on the event
608 loop: Every watcher keeps one reference, and as long as the reference
609 count is nonzero, <code>ev_loop</code> will not return on its own. If you have
610 a watcher you never unregister that should not keep <code>ev_loop</code> from
611 returning, ev_unref() after starting, and ev_ref() before stopping it. For
612 example, libev itself uses this for its internal signal pipe: It is not
613 visible to the libev user and should not keep <code>ev_loop</code> from exiting if
614 no event watchers registered by it are active. It is also an excellent
615 way to do this for generic recurring timers or from within third-party
616 libraries. Just remember to <i>unref after start</i> and <i>ref before stop</i>.</p>
617 <p>Example: Create a signal watcher, but keep it from keeping <code>ev_loop</code>
618 running when nothing else is active.</p>
619 <pre> struct ev_signal exitsig;
620 ev_signal_init (&amp;exitsig, sig_cb, SIGINT);
621 ev_signal_start (loop, &amp;exitsig);
622 evf_unref (loop);
624 </pre>
625 <p>Example: For some weird reason, unregister the above signal handler again.</p>
626 <pre> ev_ref (loop);
627 ev_signal_stop (loop, &amp;exitsig);
629 </pre>
630 </dd>
631 </dl>
637 </div>
640 <p>A watcher is a structure that you create and register to record your
641 interest in some event. For instance, if you want to wait for STDIN to
642 become readable, you would create an <code>ev_io</code> watcher for that:</p>
643 <pre> static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents)
644 {
645 ev_io_stop (w);
646 ev_unloop (loop, EVUNLOOP_ALL);
647 }
649 struct ev_loop *loop = ev_default_loop (0);
650 struct ev_io stdin_watcher;
651 ev_init (&amp;stdin_watcher, my_cb);
652 ev_io_set (&amp;stdin_watcher, STDIN_FILENO, EV_READ);
653 ev_io_start (loop, &amp;stdin_watcher);
654 ev_loop (loop, 0);
656 </pre>
657 <p>As you can see, you are responsible for allocating the memory for your
658 watcher structures (and it is usually a bad idea to do this on the stack,
659 although this can sometimes be quite valid).</p>
660 <p>Each watcher structure must be initialised by a call to <code>ev_init
661 (watcher *, callback)</code>, which expects a callback to be provided. This
662 callback gets invoked each time the event occurs (or, in the case of io
663 watchers, each time the event loop detects that the file descriptor given
664 is readable and/or writable).</p>
665 <p>Each watcher type has its own <code>ev_&lt;type&gt;_set (watcher *, ...)</code> macro
666 with arguments specific to this watcher type. There is also a macro
667 to combine initialisation and setting in one call: <code>ev_&lt;type&gt;_init
668 (watcher *, callback, ...)</code>.</p>
669 <p>To make the watcher actually watch out for events, you have to start it
670 with a watcher-specific start function (<code>ev_&lt;type&gt;_start (loop, watcher
671 *)</code>), and you can stop watching for events at any time by calling the
672 corresponding stop function (<code>ev_&lt;type&gt;_stop (loop, watcher *)</code>.</p>
673 <p>As long as your watcher is active (has been started but not stopped) you
674 must not touch the values stored in it. Most specifically you must never
675 reinitialise it or call its <code>set</code> macro.</p>
676 <p>Each and every callback receives the event loop pointer as first, the
677 registered watcher structure as second, and a bitset of received events as
678 third argument.</p>
679 <p>The received events usually include a single bit per event type received
680 (you can receive multiple events at the same time). The possible bit masks
681 are:</p>
682 <dl>
683 <dt><code>EV_READ</code></dt>
684 <dt><code>EV_WRITE</code></dt>
685 <dd>
686 <p>The file descriptor in the <code>ev_io</code> watcher has become readable and/or
687 writable.</p>
688 </dd>
689 <dt><code>EV_TIMEOUT</code></dt>
690 <dd>
691 <p>The <code>ev_timer</code> watcher has timed out.</p>
692 </dd>
693 <dt><code>EV_PERIODIC</code></dt>
694 <dd>
695 <p>The <code>ev_periodic</code> watcher has timed out.</p>
696 </dd>
697 <dt><code>EV_SIGNAL</code></dt>
698 <dd>
699 <p>The signal specified in the <code>ev_signal</code> watcher has been received by a thread.</p>
700 </dd>
701 <dt><code>EV_CHILD</code></dt>
702 <dd>
703 <p>The pid specified in the <code>ev_child</code> watcher has received a status change.</p>
704 </dd>
705 <dt><code>EV_STAT</code></dt>
706 <dd>
707 <p>The path specified in the <code>ev_stat</code> watcher changed its attributes somehow.</p>
708 </dd>
709 <dt><code>EV_IDLE</code></dt>
710 <dd>
711 <p>The <code>ev_idle</code> watcher has determined that you have nothing better to do.</p>
712 </dd>
713 <dt><code>EV_PREPARE</code></dt>
714 <dt><code>EV_CHECK</code></dt>
715 <dd>
716 <p>All <code>ev_prepare</code> watchers are invoked just <i>before</i> <code>ev_loop</code> starts
717 to gather new events, and all <code>ev_check</code> watchers are invoked just after
718 <code>ev_loop</code> has gathered them, but before it invokes any callbacks for any
719 received events. Callbacks of both watcher types can start and stop as
720 many watchers as they want, and all of them will be taken into account
721 (for example, a <code>ev_prepare</code> watcher might start an idle watcher to keep
722 <code>ev_loop</code> from blocking).</p>
723 </dd>
724 <dt><code>EV_EMBED</code></dt>
725 <dd>
726 <p>The embedded event loop specified in the <code>ev_embed</code> watcher needs attention.</p>
727 </dd>
728 <dt><code>EV_FORK</code></dt>
729 <dd>
730 <p>The event loop has been resumed in the child process after fork (see
731 <code>ev_fork</code>).</p>
732 </dd>
733 <dt><code>EV_ERROR</code></dt>
734 <dd>
735 <p>An unspecified error has occured, the watcher has been stopped. This might
736 happen because the watcher could not be properly started because libev
737 ran out of memory, a file descriptor was found to be closed or any other
738 problem. You best act on it by reporting the problem and somehow coping
739 with the watcher being stopped.</p>
740 <p>Libev will usually signal a few &quot;dummy&quot; events together with an error,
741 for example it might indicate that a fd is readable or writable, and if
742 your callbacks is well-written it can just attempt the operation and cope
743 with the error from read() or write(). This will not work in multithreaded
744 programs, though, so beware.</p>
745 </dd>
746 </dl>
748 </div>
751 <p>In the following description, <code>TYPE</code> stands for the watcher type,
752 e.g. <code>timer</code> for <code>ev_timer</code> watchers and <code>io</code> for <code>ev_io</code> watchers.</p>
753 <dl>
754 <dt><code>ev_init</code> (ev_TYPE *watcher, callback)</dt>
755 <dd>
756 <p>This macro initialises the generic portion of a watcher. The contents
757 of the watcher object can be arbitrary (so <code>malloc</code> will do). Only
758 the generic parts of the watcher are initialised, you <i>need</i> to call
759 the type-specific <code>ev_TYPE_set</code> macro afterwards to initialise the
760 type-specific parts. For each type there is also a <code>ev_TYPE_init</code> macro
761 which rolls both calls into one.</p>
762 <p>You can reinitialise a watcher at any time as long as it has been stopped
763 (or never started) and there are no pending events outstanding.</p>
764 <p>The callback is always of type <code>void (*)(ev_loop *loop, ev_TYPE *watcher,
765 int revents)</code>.</p>
766 </dd>
767 <dt><code>ev_TYPE_set</code> (ev_TYPE *, [args])</dt>
768 <dd>
769 <p>This macro initialises the type-specific parts of a watcher. You need to
770 call <code>ev_init</code> at least once before you call this macro, but you can
771 call <code>ev_TYPE_set</code> any number of times. You must not, however, call this
772 macro on a watcher that is active (it can be pending, however, which is a
773 difference to the <code>ev_init</code> macro).</p>
774 <p>Although some watcher types do not have type-specific arguments
775 (e.g. <code>ev_prepare</code>) you still need to call its <code>set</code> macro.</p>
776 </dd>
777 <dt><code>ev_TYPE_init</code> (ev_TYPE *watcher, callback, [args])</dt>
778 <dd>
779 <p>This convinience macro rolls both <code>ev_init</code> and <code>ev_TYPE_set</code> macro
780 calls into a single call. This is the most convinient method to initialise
781 a watcher. The same limitations apply, of course.</p>
782 </dd>
783 <dt><code>ev_TYPE_start</code> (loop *, ev_TYPE *watcher)</dt>
784 <dd>
785 <p>Starts (activates) the given watcher. Only active watchers will receive
786 events. If the watcher is already active nothing will happen.</p>
787 </dd>
788 <dt><code>ev_TYPE_stop</code> (loop *, ev_TYPE *watcher)</dt>
789 <dd>
790 <p>Stops the given watcher again (if active) and clears the pending
791 status. It is possible that stopped watchers are pending (for example,
792 non-repeating timers are being stopped when they become pending), but
793 <code>ev_TYPE_stop</code> ensures that the watcher is neither active nor pending. If
794 you want to free or reuse the memory used by the watcher it is therefore a
795 good idea to always call its <code>ev_TYPE_stop</code> function.</p>
796 </dd>
797 <dt>bool ev_is_active (ev_TYPE *watcher)</dt>
798 <dd>
799 <p>Returns a true value iff the watcher is active (i.e. it has been started
800 and not yet been stopped). As long as a watcher is active you must not modify
801 it.</p>
802 </dd>
803 <dt>bool ev_is_pending (ev_TYPE *watcher)</dt>
804 <dd>
805 <p>Returns a true value iff the watcher is pending, (i.e. it has outstanding
806 events but its callback has not yet been invoked). As long as a watcher
807 is pending (but not active) you must not call an init function on it (but
808 <code>ev_TYPE_set</code> is safe), you must not change its priority, and you must
809 make sure the watcher is available to libev (e.g. you cannot <code>free ()</code>
810 it).</p>
811 </dd>
812 <dt>callback ev_cb (ev_TYPE *watcher)</dt>
813 <dd>
814 <p>Returns the callback currently set on the watcher.</p>
815 </dd>
816 <dt>ev_cb_set (ev_TYPE *watcher, callback)</dt>
817 <dd>
818 <p>Change the callback. You can change the callback at virtually any time
819 (modulo threads).</p>
820 </dd>
821 <dt>ev_set_priority (ev_TYPE *watcher, priority)</dt>
822 <dt>int ev_priority (ev_TYPE *watcher)</dt>
823 <dd>
824 <p>Set and query the priority of the watcher. The priority is a small
825 integer between <code>EV_MAXPRI</code> (default: <code>2</code>) and <code>EV_MINPRI</code>
826 (default: <code>-2</code>). Pending watchers with higher priority will be invoked
827 before watchers with lower priority, but priority will not keep watchers
828 from being executed (except for <code>ev_idle</code> watchers).</p>
829 <p>This means that priorities are <i>only</i> used for ordering callback
830 invocation after new events have been received. This is useful, for
831 example, to reduce latency after idling, or more often, to bind two
832 watchers on the same event and make sure one is called first.</p>
833 <p>If you need to suppress invocation when higher priority events are pending
834 you need to look at <code>ev_idle</code> watchers, which provide this functionality.</p>
835 <p>You <i>must not</i> change the priority of a watcher as long as it is active or
836 pending.</p>
837 <p>The default priority used by watchers when no priority has been set is
838 always <code>0</code>, which is supposed to not be too high and not be too low :).</p>
839 <p>Setting a priority outside the range of <code>EV_MINPRI</code> to <code>EV_MAXPRI</code> is
840 fine, as long as you do not mind that the priority value you query might
841 or might not have been adjusted to be within valid range.</p>
842 </dd>
843 <dt>ev_invoke (loop, ev_TYPE *watcher, int revents)</dt>
844 <dd>
845 <p>Invoke the <code>watcher</code> with the given <code>loop</code> and <code>revents</code>. Neither
846 <code>loop</code> nor <code>revents</code> need to be valid as long as the watcher callback
847 can deal with that fact.</p>
848 </dd>
849 <dt>int ev_clear_pending (loop, ev_TYPE *watcher)</dt>
850 <dd>
851 <p>If the watcher is pending, this function returns clears its pending status
852 and returns its <code>revents</code> bitset (as if its callback was invoked). If the
853 watcher isn't pending it does nothing and returns <code>0</code>.</p>
854 </dd>
855 </dl>
861 </div>
864 <p>Each watcher has, by default, a member <code>void *data</code> that you can change
865 and read at any time, libev will completely ignore it. This can be used
866 to associate arbitrary data with your watcher. If you need more data and
867 don't want to allocate memory and store a pointer to it in that data
868 member, you can also &quot;subclass&quot; the watcher type and provide your own
869 data:</p>
870 <pre> struct my_io
871 {
872 struct ev_io io;
873 int otherfd;
874 void *somedata;
875 struct whatever *mostinteresting;
876 }
878 </pre>
879 <p>And since your callback will be called with a pointer to the watcher, you
880 can cast it back to your own type:</p>
881 <pre> static void my_cb (struct ev_loop *loop, struct ev_io *w_, int revents)
882 {
883 struct my_io *w = (struct my_io *)w_;
884 ...
885 }
887 </pre>
888 <p>More interesting and less C-conformant ways of casting your callback type
889 instead have been omitted.</p>
890 <p>Another common scenario is having some data structure with multiple
891 watchers:</p>
892 <pre> struct my_biggy
893 {
894 int some_data;
895 ev_timer t1;
896 ev_timer t2;
897 }
899 </pre>
900 <p>In this case getting the pointer to <code>my_biggy</code> is a bit more complicated,
901 you need to use <code>offsetof</code>:</p>
902 <pre> #include &lt;stddef.h&gt;
904 static void
905 t1_cb (EV_P_ struct ev_timer *w, int revents)
906 {
907 struct my_biggy big = (struct my_biggy *
908 (((char *)w) - offsetof (struct my_biggy, t1));
909 }
911 static void
912 t2_cb (EV_P_ struct ev_timer *w, int revents)
913 {
914 struct my_biggy big = (struct my_biggy *
915 (((char *)w) - offsetof (struct my_biggy, t2));
916 }
921 </pre>
923 </div>
926 <p>This section describes each watcher in detail, but will not repeat
927 information given in the last section. Any initialisation/set macros,
928 functions and members specific to the watcher type are explained.</p>
929 <p>Members are additionally marked with either <i>[read-only]</i>, meaning that,
930 while the watcher is active, you can look at the member and expect some
931 sensible content, but you must not modify it (you can modify it while the
932 watcher is stopped to your hearts content), or <i>[read-write]</i>, which
933 means you can expect it to have some sensible content while the watcher
934 is active, but you can also modify it. Modifying it may not do something
935 sensible or take immediate effect (or do anything at all), but libev will
936 not crash or malfunction in any way.</p>
942 </div>
943 <h2 id="code_ev_io_code_is_this_file_descrip"><code>ev_io</code> - is this file descriptor readable or writable?</h2>
944 <div id="code_ev_io_code_is_this_file_descrip-2">
945 <p>I/O watchers check whether a file descriptor is readable or writable
946 in each iteration of the event loop, or, more precisely, when reading
947 would not block the process and writing would at least be able to write
948 some data. This behaviour is called level-triggering because you keep
949 receiving events as long as the condition persists. Remember you can stop
950 the watcher if you don't want to act on the event and neither want to
951 receive future events.</p>
952 <p>In general you can register as many read and/or write event watchers per
953 fd as you want (as long as you don't confuse yourself). Setting all file
954 descriptors to non-blocking mode is also usually a good idea (but not
955 required if you know what you are doing).</p>
956 <p>You have to be careful with dup'ed file descriptors, though. Some backends
957 (the linux epoll backend is a notable example) cannot handle dup'ed file
958 descriptors correctly if you register interest in two or more fds pointing
959 to the same underlying file/socket/etc. description (that is, they share
960 the same underlying &quot;file open&quot;).</p>
961 <p>If you must do this, then force the use of a known-to-be-good backend
962 (at the time of this writing, this includes only <code>EVBACKEND_SELECT</code> and
963 <code>EVBACKEND_POLL</code>).</p>
964 <p>Another thing you have to watch out for is that it is quite easy to
965 receive &quot;spurious&quot; readyness notifications, that is your callback might
966 be called with <code>EV_READ</code> but a subsequent <code>read</code>(2) will actually block
967 because there is no data. Not only are some backends known to create a
968 lot of those (for example solaris ports), it is very easy to get into
969 this situation even with a relatively standard program structure. Thus
970 it is best to always use non-blocking I/O: An extra <code>read</code>(2) returning
971 <code>EAGAIN</code> is far preferable to a program hanging until some data arrives.</p>
972 <p>If you cannot run the fd in non-blocking mode (for example you should not
973 play around with an Xlib connection), then you have to seperately re-test
974 whether a file descriptor is really ready with a known-to-be good interface
975 such as poll (fortunately in our Xlib example, Xlib already does this on
976 its own, so its quite safe to use).</p>
978 </div>
979 <h3 id="The_special_problem_of_disappearing_">The special problem of disappearing file descriptors</h3>
980 <div id="The_special_problem_of_disappearing_-2">
981 <p>Some backends (e.g kqueue, epoll) need to be told about closing a file
982 descriptor (either by calling <code>close</code> explicitly or by any other means,
983 such as <code>dup</code>). The reason is that you register interest in some file
984 descriptor, but when it goes away, the operating system will silently drop
985 this interest. If another file descriptor with the same number then is
986 registered with libev, there is no efficient way to see that this is, in
987 fact, a different file descriptor.</p>
988 <p>To avoid having to explicitly tell libev about such cases, libev follows
989 the following policy: Each time <code>ev_io_set</code> is being called, libev
990 will assume that this is potentially a new file descriptor, otherwise
991 it is assumed that the file descriptor stays the same. That means that
992 you <i>have</i> to call <code>ev_io_set</code> (or <code>ev_io_init</code>) when you change the
993 descriptor even if the file descriptor number itself did not change.</p>
994 <p>This is how one would do it normally anyway, the important point is that
995 the libev application should not optimise around libev but should leave
996 optimisations to libev.</p>
1002 </div>
1003 <h3 id="Watcher_Specific_Functions">Watcher-Specific Functions</h3>
1004 <div id="Watcher_Specific_Functions_CONTENT">
1005 <dl>
1006 <dt>ev_io_init (ev_io *, callback, int fd, int events)</dt>
1007 <dt>ev_io_set (ev_io *, int fd, int events)</dt>
1008 <dd>
1009 <p>Configures an <code>ev_io</code> watcher. The <code>fd</code> is the file descriptor to
1010 rceeive events for and events is either <code>EV_READ</code>, <code>EV_WRITE</code> or
1011 <code>EV_READ | EV_WRITE</code> to receive the given events.</p>
1012 </dd>
1013 <dt>int fd [read-only]</dt>
1014 <dd>
1015 <p>The file descriptor being watched.</p>
1016 </dd>
1017 <dt>int events [read-only]</dt>
1018 <dd>
1019 <p>The events being watched.</p>
1020 </dd>
1021 </dl>
1022 <p>Example: Call <code>stdin_readable_cb</code> when STDIN_FILENO has become, well
1023 readable, but only once. Since it is likely line-buffered, you could
1024 attempt to read a whole line in the callback.</p>
1025 <pre> static void
1026 stdin_readable_cb (struct ev_loop *loop, struct ev_io *w, int revents)
1027 {
1028 ev_io_stop (loop, w);
1029 .. read from stdin here (or from w-&gt;fd) and haqndle any I/O errors
1030 }
1032 ...
1033 struct ev_loop *loop = ev_default_init (0);
1034 struct ev_io stdin_readable;
1035 ev_io_init (&amp;stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
1036 ev_io_start (loop, &amp;stdin_readable);
1037 ev_loop (loop, 0);
1042 </pre>
1044 </div>
1045 <h2 id="code_ev_timer_code_relative_and_opti"><code>ev_timer</code> - relative and optionally repeating timeouts</h2>
1046 <div id="code_ev_timer_code_relative_and_opti-2">
1047 <p>Timer watchers are simple relative timers that generate an event after a
1048 given time, and optionally repeating in regular intervals after that.</p>
1049 <p>The timers are based on real time, that is, if you register an event that
1050 times out after an hour and you reset your system clock to last years
1051 time, it will still time out after (roughly) and hour. &quot;Roughly&quot; because
1052 detecting time jumps is hard, and some inaccuracies are unavoidable (the
1053 monotonic clock option helps a lot here).</p>
1054 <p>The relative timeouts are calculated relative to the <code>ev_now ()</code>
1055 time. This is usually the right thing as this timestamp refers to the time
1056 of the event triggering whatever timeout you are modifying/starting. If
1057 you suspect event processing to be delayed and you <i>need</i> to base the timeout
1058 on the current time, use something like this to adjust for this:</p>
1059 <pre> ev_timer_set (&amp;timer, after + ev_now () - ev_time (), 0.);
1061 </pre>
1062 <p>The callback is guarenteed to be invoked only when its timeout has passed,
1063 but if multiple timers become ready during the same loop iteration then
1064 order of execution is undefined.</p>
1066 </div>
1067 <h3 id="Watcher_Specific_Functions_and_Data_">Watcher-Specific Functions and Data Members</h3>
1068 <div id="Watcher_Specific_Functions_and_Data_-2">
1069 <dl>
1070 <dt>ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)</dt>
1071 <dt>ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)</dt>
1072 <dd>
1073 <p>Configure the timer to trigger after <code>after</code> seconds. If <code>repeat</code> is
1074 <code>0.</code>, then it will automatically be stopped. If it is positive, then the
1075 timer will automatically be configured to trigger again <code>repeat</code> seconds
1076 later, again, and again, until stopped manually.</p>
1077 <p>The timer itself will do a best-effort at avoiding drift, that is, if you
1078 configure a timer to trigger every 10 seconds, then it will trigger at
1079 exactly 10 second intervals. If, however, your program cannot keep up with
1080 the timer (because it takes longer than those 10 seconds to do stuff) the
1081 timer will not fire more than once per event loop iteration.</p>
1082 </dd>
1083 <dt>ev_timer_again (loop)</dt>
1084 <dd>
1085 <p>This will act as if the timer timed out and restart it again if it is
1086 repeating. The exact semantics are:</p>
1087 <p>If the timer is pending, its pending status is cleared.</p>
1088 <p>If the timer is started but nonrepeating, stop it (as if it timed out).</p>
1089 <p>If the timer is repeating, either start it if necessary (with the
1090 <code>repeat</code> value), or reset the running timer to the <code>repeat</code> value.</p>
1091 <p>This sounds a bit complicated, but here is a useful and typical
1092 example: Imagine you have a tcp connection and you want a so-called idle
1093 timeout, that is, you want to be called when there have been, say, 60
1094 seconds of inactivity on the socket. The easiest way to do this is to
1095 configure an <code>ev_timer</code> with a <code>repeat</code> value of <code>60</code> and then call
1096 <code>ev_timer_again</code> each time you successfully read or write some data. If
1097 you go into an idle state where you do not expect data to travel on the
1098 socket, you can <code>ev_timer_stop</code> the timer, and <code>ev_timer_again</code> will
1099 automatically restart it if need be.</p>
1100 <p>That means you can ignore the <code>after</code> value and <code>ev_timer_start</code>
1101 altogether and only ever use the <code>repeat</code> value and <code>ev_timer_again</code>:</p>
1102 <pre> ev_timer_init (timer, callback, 0., 5.);
1103 ev_timer_again (loop, timer);
1104 ...
1105 timer-&gt;again = 17.;
1106 ev_timer_again (loop, timer);
1107 ...
1108 timer-&gt;again = 10.;
1109 ev_timer_again (loop, timer);
1111 </pre>
1112 <p>This is more slightly efficient then stopping/starting the timer each time
1113 you want to modify its timeout value.</p>
1114 </dd>
1115 <dt>ev_tstamp repeat [read-write]</dt>
1116 <dd>
1117 <p>The current <code>repeat</code> value. Will be used each time the watcher times out
1118 or <code>ev_timer_again</code> is called and determines the next timeout (if any),
1119 which is also when any modifications are taken into account.</p>
1120 </dd>
1121 </dl>
1122 <p>Example: Create a timer that fires after 60 seconds.</p>
1123 <pre> static void
1124 one_minute_cb (struct ev_loop *loop, struct ev_timer *w, int revents)
1125 {
1126 .. one minute over, w is actually stopped right here
1127 }
1129 struct ev_timer mytimer;
1130 ev_timer_init (&amp;mytimer, one_minute_cb, 60., 0.);
1131 ev_timer_start (loop, &amp;mytimer);
1133 </pre>
1134 <p>Example: Create a timeout timer that times out after 10 seconds of
1135 inactivity.</p>
1136 <pre> static void
1137 timeout_cb (struct ev_loop *loop, struct ev_timer *w, int revents)
1138 {
1139 .. ten seconds without any activity
1140 }
1142 struct ev_timer mytimer;
1143 ev_timer_init (&amp;mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
1144 ev_timer_again (&amp;mytimer); /* start timer */
1145 ev_loop (loop, 0);
1147 // and in some piece of code that gets executed on any &quot;activity&quot;:
1148 // reset the timeout to start ticking again at 10 seconds
1149 ev_timer_again (&amp;mytimer);
1154 </pre>
1156 </div>
1157 <h2 id="code_ev_periodic_code_to_cron_or_not"><code>ev_periodic</code> - to cron or not to cron?</h2>
1158 <div id="code_ev_periodic_code_to_cron_or_not-2">
1159 <p>Periodic watchers are also timers of a kind, but they are very versatile
1160 (and unfortunately a bit complex).</p>
1161 <p>Unlike <code>ev_timer</code>'s, they are not based on real time (or relative time)
1162 but on wallclock time (absolute time). You can tell a periodic watcher
1163 to trigger &quot;at&quot; some specific point in time. For example, if you tell a
1164 periodic watcher to trigger in 10 seconds (by specifiying e.g. <code>ev_now ()
1165 + 10.</code>) and then reset your system clock to the last year, then it will
1166 take a year to trigger the event (unlike an <code>ev_timer</code>, which would trigger
1167 roughly 10 seconds later).</p>
1168 <p>They can also be used to implement vastly more complex timers, such as
1169 triggering an event on each midnight, local time or other, complicated,
1170 rules.</p>
1171 <p>As with timers, the callback is guarenteed to be invoked only when the
1172 time (<code>at</code>) has been passed, but if multiple periodic timers become ready
1173 during the same loop iteration then order of execution is undefined.</p>
1175 </div>
1176 <h3 id="Watcher_Specific_Functions_and_Data_-3">Watcher-Specific Functions and Data Members</h3>
1177 <div id="Watcher_Specific_Functions_and_Data_-2">
1178 <dl>
1179 <dt>ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)</dt>
1180 <dt>ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)</dt>
1181 <dd>
1182 <p>Lots of arguments, lets sort it out... There are basically three modes of
1183 operation, and we will explain them from simplest to complex:</p>
1184 <p>
1185 <dl>
1186 <dt>* absolute timer (at = time, interval = reschedule_cb = 0)</dt>
1187 <dd>
1188 <p>In this configuration the watcher triggers an event at the wallclock time
1189 <code>at</code> and doesn't repeat. It will not adjust when a time jump occurs,
1190 that is, if it is to be run at January 1st 2011 then it will run when the
1191 system time reaches or surpasses this time.</p>
1192 </dd>
1193 <dt>* non-repeating interval timer (at = offset, interval &gt; 0, reschedule_cb = 0)</dt>
1194 <dd>
1195 <p>In this mode the watcher will always be scheduled to time out at the next
1196 <code>at + N * interval</code> time (for some integer N, which can also be negative)
1197 and then repeat, regardless of any time jumps.</p>
1198 <p>This can be used to create timers that do not drift with respect to system
1199 time:</p>
1200 <pre> ev_periodic_set (&amp;periodic, 0., 3600., 0);
1202 </pre>
1203 <p>This doesn't mean there will always be 3600 seconds in between triggers,
1204 but only that the the callback will be called when the system time shows a
1205 full hour (UTC), or more correctly, when the system time is evenly divisible
1206 by 3600.</p>
1207 <p>Another way to think about it (for the mathematically inclined) is that
1208 <code>ev_periodic</code> will try to run the callback in this mode at the next possible
1209 time where <code>time = at (mod interval)</code>, regardless of any time jumps.</p>
1210 <p>For numerical stability it is preferable that the <code>at</code> value is near
1211 <code>ev_now ()</code> (the current time), but there is no range requirement for
1212 this value.</p>
1213 </dd>
1214 <dt>* manual reschedule mode (at and interval ignored, reschedule_cb = callback)</dt>
1215 <dd>
1216 <p>In this mode the values for <code>interval</code> and <code>at</code> are both being
1217 ignored. Instead, each time the periodic watcher gets scheduled, the
1218 reschedule callback will be called with the watcher as first, and the
1219 current time as second argument.</p>
1220 <p>NOTE: <i>This callback MUST NOT stop or destroy any periodic watcher,
1221 ever, or make any event loop modifications</i>. If you need to stop it,
1222 return <code>now + 1e30</code> (or so, fudge fudge) and stop it afterwards (e.g. by
1223 starting an <code>ev_prepare</code> watcher, which is legal).</p>
1224 <p>Its prototype is <code>ev_tstamp (*reschedule_cb)(struct ev_periodic *w,
1225 ev_tstamp now)</code>, e.g.:</p>
1226 <pre> static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)
1227 {
1228 return now + 60.;
1229 }
1231 </pre>
1232 <p>It must return the next time to trigger, based on the passed time value
1233 (that is, the lowest time value larger than to the second argument). It
1234 will usually be called just before the callback will be triggered, but
1235 might be called at other times, too.</p>
1236 <p>NOTE: <i>This callback must always return a time that is later than the
1237 passed <code>now</code> value</i>. Not even <code>now</code> itself will do, it <i>must</i> be larger.</p>
1238 <p>This can be used to create very complex timers, such as a timer that
1239 triggers on each midnight, local time. To do this, you would calculate the
1240 next midnight after <code>now</code> and return the timestamp value for this. How
1241 you do this is, again, up to you (but it is not trivial, which is the main
1242 reason I omitted it as an example).</p>
1243 </dd>
1244 </dl>
1245 </p>
1246 </dd>
1247 <dt>ev_periodic_again (loop, ev_periodic *)</dt>
1248 <dd>
1249 <p>Simply stops and restarts the periodic watcher again. This is only useful
1250 when you changed some parameters or the reschedule callback would return
1251 a different time than the last time it was called (e.g. in a crond like
1252 program when the crontabs have changed).</p>
1253 </dd>
1254 <dt>ev_tstamp offset [read-write]</dt>
1255 <dd>
1256 <p>When repeating, this contains the offset value, otherwise this is the
1257 absolute point in time (the <code>at</code> value passed to <code>ev_periodic_set</code>).</p>
1258 <p>Can be modified any time, but changes only take effect when the periodic
1259 timer fires or <code>ev_periodic_again</code> is being called.</p>
1260 </dd>
1261 <dt>ev_tstamp interval [read-write]</dt>
1262 <dd>
1263 <p>The current interval value. Can be modified any time, but changes only
1264 take effect when the periodic timer fires or <code>ev_periodic_again</code> is being
1265 called.</p>
1266 </dd>
1267 <dt>ev_tstamp (*reschedule_cb)(struct ev_periodic *w, ev_tstamp now) [read-write]</dt>
1268 <dd>
1269 <p>The current reschedule callback, or <code>0</code>, if this functionality is
1270 switched off. Can be changed any time, but changes only take effect when
1271 the periodic timer fires or <code>ev_periodic_again</code> is being called.</p>
1272 </dd>
1273 </dl>
1274 <p>Example: Call a callback every hour, or, more precisely, whenever the
1275 system clock is divisible by 3600. The callback invocation times have
1276 potentially a lot of jittering, but good long-term stability.</p>
1277 <pre> static void
1278 clock_cb (struct ev_loop *loop, struct ev_io *w, int revents)
1279 {
1280 ... its now a full hour (UTC, or TAI or whatever your clock follows)
1281 }
1283 struct ev_periodic hourly_tick;
1284 ev_periodic_init (&amp;hourly_tick, clock_cb, 0., 3600., 0);
1285 ev_periodic_start (loop, &amp;hourly_tick);
1287 </pre>
1288 <p>Example: The same as above, but use a reschedule callback to do it:</p>
1289 <pre> #include &lt;math.h&gt;
1291 static ev_tstamp
1292 my_scheduler_cb (struct ev_periodic *w, ev_tstamp now)
1293 {
1294 return fmod (now, 3600.) + 3600.;
1295 }
1297 ev_periodic_init (&amp;hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
1299 </pre>
1300 <p>Example: Call a callback every hour, starting now:</p>
1301 <pre> struct ev_periodic hourly_tick;
1302 ev_periodic_init (&amp;hourly_tick, clock_cb,
1303 fmod (ev_now (loop), 3600.), 3600., 0);
1304 ev_periodic_start (loop, &amp;hourly_tick);
1309 </pre>
1311 </div>
1312 <h2 id="code_ev_signal_code_signal_me_when_a"><code>ev_signal</code> - signal me when a signal gets signalled!</h2>
1313 <div id="code_ev_signal_code_signal_me_when_a-2">
1314 <p>Signal watchers will trigger an event when the process receives a specific
1315 signal one or more times. Even though signals are very asynchronous, libev
1316 will try it's best to deliver signals synchronously, i.e. as part of the
1317 normal event processing, like any other event.</p>
1318 <p>You can configure as many watchers as you like per signal. Only when the
1319 first watcher gets started will libev actually register a signal watcher
1320 with the kernel (thus it coexists with your own signal handlers as long
1321 as you don't register any with libev). Similarly, when the last signal
1322 watcher for a signal is stopped libev will reset the signal handler to
1323 SIG_DFL (regardless of what it was set to before).</p>
1325 </div>
1326 <h3 id="Watcher_Specific_Functions_and_Data_-4">Watcher-Specific Functions and Data Members</h3>
1327 <div id="Watcher_Specific_Functions_and_Data_-2-2">
1328 <dl>
1329 <dt>ev_signal_init (ev_signal *, callback, int signum)</dt>
1330 <dt>ev_signal_set (ev_signal *, int signum)</dt>
1331 <dd>
1332 <p>Configures the watcher to trigger on the given signal number (usually one
1333 of the <code>SIGxxx</code> constants).</p>
1334 </dd>
1335 <dt>int signum [read-only]</dt>
1336 <dd>
1337 <p>The signal the watcher watches out for.</p>
1338 </dd>
1339 </dl>
1345 </div>
1346 <h2 id="code_ev_child_code_watch_out_for_pro"><code>ev_child</code> - watch out for process status changes</h2>
1347 <div id="code_ev_child_code_watch_out_for_pro-2">
1348 <p>Child watchers trigger when your process receives a SIGCHLD in response to
1349 some child status changes (most typically when a child of yours dies).</p>
1351 </div>
1352 <h3 id="Watcher_Specific_Functions_and_Data_-5">Watcher-Specific Functions and Data Members</h3>
1353 <div id="Watcher_Specific_Functions_and_Data_-2-3">
1354 <dl>
1355 <dt>ev_child_init (ev_child *, callback, int pid)</dt>
1356 <dt>ev_child_set (ev_child *, int pid)</dt>
1357 <dd>
1358 <p>Configures the watcher to wait for status changes of process <code>pid</code> (or
1359 <i>any</i> process if <code>pid</code> is specified as <code>0</code>). The callback can look
1360 at the <code>rstatus</code> member of the <code>ev_child</code> watcher structure to see
1361 the status word (use the macros from <code>sys/wait.h</code> and see your systems
1362 <code>waitpid</code> documentation). The <code>rpid</code> member contains the pid of the
1363 process causing the status change.</p>
1364 </dd>
1365 <dt>int pid [read-only]</dt>
1366 <dd>
1367 <p>The process id this watcher watches out for, or <code>0</code>, meaning any process id.</p>
1368 </dd>
1369 <dt>int rpid [read-write]</dt>
1370 <dd>
1371 <p>The process id that detected a status change.</p>
1372 </dd>
1373 <dt>int rstatus [read-write]</dt>
1374 <dd>
1375 <p>The process exit/trace status caused by <code>rpid</code> (see your systems
1376 <code>waitpid</code> and <code>sys/wait.h</code> documentation for details).</p>
1377 </dd>
1378 </dl>
1379 <p>Example: Try to exit cleanly on SIGINT and SIGTERM.</p>
1380 <pre> static void
1381 sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents)
1382 {
1383 ev_unloop (loop, EVUNLOOP_ALL);
1384 }
1386 struct ev_signal signal_watcher;
1387 ev_signal_init (&amp;signal_watcher, sigint_cb, SIGINT);
1388 ev_signal_start (loop, &amp;sigint_cb);
1393 </pre>
1395 </div>
1396 <h2 id="code_ev_stat_code_did_the_file_attri"><code>ev_stat</code> - did the file attributes just change?</h2>
1397 <div id="code_ev_stat_code_did_the_file_attri-2">
1398 <p>This watches a filesystem path for attribute changes. That is, it calls
1399 <code>stat</code> regularly (or when the OS says it changed) and sees if it changed
1400 compared to the last time, invoking the callback if it did.</p>
1401 <p>The path does not need to exist: changing from &quot;path exists&quot; to &quot;path does
1402 not exist&quot; is a status change like any other. The condition &quot;path does
1403 not exist&quot; is signified by the <code>st_nlink</code> field being zero (which is
1404 otherwise always forced to be at least one) and all the other fields of
1405 the stat buffer having unspecified contents.</p>
1406 <p>The path <i>should</i> be absolute and <i>must not</i> end in a slash. If it is
1407 relative and your working directory changes, the behaviour is undefined.</p>
1408 <p>Since there is no standard to do this, the portable implementation simply
1409 calls <code>stat (2)</code> regularly on the path to see if it changed somehow. You
1410 can specify a recommended polling interval for this case. If you specify
1411 a polling interval of <code>0</code> (highly recommended!) then a <i>suitable,
1412 unspecified default</i> value will be used (which you can expect to be around
1413 five seconds, although this might change dynamically). Libev will also
1414 impose a minimum interval which is currently around <code>0.1</code>, but thats
1415 usually overkill.</p>
1416 <p>This watcher type is not meant for massive numbers of stat watchers,
1417 as even with OS-supported change notifications, this can be
1418 resource-intensive.</p>
1419 <p>At the time of this writing, only the Linux inotify interface is
1420 implemented (implementing kqueue support is left as an exercise for the
1421 reader). Inotify will be used to give hints only and should not change the
1422 semantics of <code>ev_stat</code> watchers, which means that libev sometimes needs
1423 to fall back to regular polling again even with inotify, but changes are
1424 usually detected immediately, and if the file exists there will be no
1425 polling.</p>
1427 </div>
1428 <h3 id="Watcher_Specific_Functions_and_Data_-6">Watcher-Specific Functions and Data Members</h3>
1429 <div id="Watcher_Specific_Functions_and_Data_-2-4">
1430 <dl>
1431 <dt>ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)</dt>
1432 <dt>ev_stat_set (ev_stat *, const char *path, ev_tstamp interval)</dt>
1433 <dd>
1434 <p>Configures the watcher to wait for status changes of the given
1435 <code>path</code>. The <code>interval</code> is a hint on how quickly a change is expected to
1436 be detected and should normally be specified as <code>0</code> to let libev choose
1437 a suitable value. The memory pointed to by <code>path</code> must point to the same
1438 path for as long as the watcher is active.</p>
1439 <p>The callback will be receive <code>EV_STAT</code> when a change was detected,
1440 relative to the attributes at the time the watcher was started (or the
1441 last change was detected).</p>
1442 </dd>
1443 <dt>ev_stat_stat (ev_stat *)</dt>
1444 <dd>
1445 <p>Updates the stat buffer immediately with new values. If you change the
1446 watched path in your callback, you could call this fucntion to avoid
1447 detecting this change (while introducing a race condition). Can also be
1448 useful simply to find out the new values.</p>
1449 </dd>
1450 <dt>ev_statdata attr [read-only]</dt>
1451 <dd>
1452 <p>The most-recently detected attributes of the file. Although the type is of
1453 <code>ev_statdata</code>, this is usually the (or one of the) <code>struct stat</code> types
1454 suitable for your system. If the <code>st_nlink</code> member is <code>0</code>, then there
1455 was some error while <code>stat</code>ing the file.</p>
1456 </dd>
1457 <dt>ev_statdata prev [read-only]</dt>
1458 <dd>
1459 <p>The previous attributes of the file. The callback gets invoked whenever
1460 <code>prev</code> != <code>attr</code>.</p>
1461 </dd>
1462 <dt>ev_tstamp interval [read-only]</dt>
1463 <dd>
1464 <p>The specified interval.</p>
1465 </dd>
1466 <dt>const char *path [read-only]</dt>
1467 <dd>
1468 <p>The filesystem path that is being watched.</p>
1469 </dd>
1470 </dl>
1471 <p>Example: Watch <code>/etc/passwd</code> for attribute changes.</p>
1472 <pre> static void
1473 passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)
1474 {
1475 /* /etc/passwd changed in some way */
1476 if (w-&gt;attr.st_nlink)
1477 {
1478 printf (&quot;passwd current size %ld\n&quot;, (long)w-&gt;attr.st_size);
1479 printf (&quot;passwd current atime %ld\n&quot;, (long)w-&gt;attr.st_mtime);
1480 printf (&quot;passwd current mtime %ld\n&quot;, (long)w-&gt;attr.st_mtime);
1481 }
1482 else
1483 /* you shalt not abuse printf for puts */
1484 puts (&quot;wow, /etc/passwd is not there, expect problems. &quot;
1485 &quot;if this is windows, they already arrived\n&quot;);
1486 }
1488 ...
1489 ev_stat passwd;
1491 ev_stat_init (&amp;passwd, passwd_cb, &quot;/etc/passwd&quot;);
1492 ev_stat_start (loop, &amp;passwd);
1497 </pre>
1499 </div>
1500 <h2 id="code_ev_idle_code_when_you_ve_got_no"><code>ev_idle</code> - when you've got nothing better to do...</h2>
1501 <div id="code_ev_idle_code_when_you_ve_got_no-2">
1502 <p>Idle watchers trigger events when no other events of the same or higher
1503 priority are pending (prepare, check and other idle watchers do not
1504 count).</p>
1505 <p>That is, as long as your process is busy handling sockets or timeouts
1506 (or even signals, imagine) of the same or higher priority it will not be
1507 triggered. But when your process is idle (or only lower-priority watchers
1508 are pending), the idle watchers are being called once per event loop
1509 iteration - until stopped, that is, or your process receives more events
1510 and becomes busy again with higher priority stuff.</p>
1511 <p>The most noteworthy effect is that as long as any idle watchers are
1512 active, the process will not block when waiting for new events.</p>
1513 <p>Apart from keeping your process non-blocking (which is a useful
1514 effect on its own sometimes), idle watchers are a good place to do
1515 &quot;pseudo-background processing&quot;, or delay processing stuff to after the
1516 event loop has handled all outstanding events.</p>
1518 </div>
1519 <h3 id="Watcher_Specific_Functions_and_Data_-7">Watcher-Specific Functions and Data Members</h3>
1520 <div id="Watcher_Specific_Functions_and_Data_-2-5">
1521 <dl>
1522 <dt>ev_idle_init (ev_signal *, callback)</dt>
1523 <dd>
1524 <p>Initialises and configures the idle watcher - it has no parameters of any
1525 kind. There is a <code>ev_idle_set</code> macro, but using it is utterly pointless,
1526 believe me.</p>
1527 </dd>
1528 </dl>
1529 <p>Example: Dynamically allocate an <code>ev_idle</code> watcher, start it, and in the
1530 callback, free it. Also, use no error checking, as usual.</p>
1531 <pre> static void
1532 idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents)
1533 {
1534 free (w);
1535 // now do something you wanted to do when the program has
1536 // no longer asnything immediate to do.
1537 }
1539 struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle));
1540 ev_idle_init (idle_watcher, idle_cb);
1541 ev_idle_start (loop, idle_cb);
1546 </pre>
1548 </div>
1549 <h2 id="code_ev_prepare_code_and_code_ev_che"><code>ev_prepare</code> and <code>ev_check</code> - customise your event loop!</h2>
1550 <div id="code_ev_prepare_code_and_code_ev_che-2">
1551 <p>Prepare and check watchers are usually (but not always) used in tandem:
1552 prepare watchers get invoked before the process blocks and check watchers
1553 afterwards.</p>
1554 <p>You <i>must not</i> call <code>ev_loop</code> or similar functions that enter
1555 the current event loop from either <code>ev_prepare</code> or <code>ev_check</code>
1556 watchers. Other loops than the current one are fine, however. The
1557 rationale behind this is that you do not need to check for recursion in
1558 those watchers, i.e. the sequence will always be <code>ev_prepare</code>, blocking,
1559 <code>ev_check</code> so if you have one watcher of each kind they will always be
1560 called in pairs bracketing the blocking call.</p>
1561 <p>Their main purpose is to integrate other event mechanisms into libev and
1562 their use is somewhat advanced. This could be used, for example, to track
1563 variable changes, implement your own watchers, integrate net-snmp or a
1564 coroutine library and lots more. They are also occasionally useful if
1565 you cache some data and want to flush it before blocking (for example,
1566 in X programs you might want to do an <code>XFlush ()</code> in an <code>ev_prepare</code>
1567 watcher).</p>
1568 <p>This is done by examining in each prepare call which file descriptors need
1569 to be watched by the other library, registering <code>ev_io</code> watchers for
1570 them and starting an <code>ev_timer</code> watcher for any timeouts (many libraries
1571 provide just this functionality). Then, in the check watcher you check for
1572 any events that occured (by checking the pending status of all watchers
1573 and stopping them) and call back into the library. The I/O and timer
1574 callbacks will never actually be called (but must be valid nevertheless,
1575 because you never know, you know?).</p>
1576 <p>As another example, the Perl Coro module uses these hooks to integrate
1577 coroutines into libev programs, by yielding to other active coroutines
1578 during each prepare and only letting the process block if no coroutines
1579 are ready to run (it's actually more complicated: it only runs coroutines
1580 with priority higher than or equal to the event loop and one coroutine
1581 of lower priority, but only once, using idle watchers to keep the event
1582 loop from blocking if lower-priority coroutines are active, thus mapping
1583 low-priority coroutines to idle/background tasks).</p>
1584 <p>It is recommended to give <code>ev_check</code> watchers highest (<code>EV_MAXPRI</code>)
1585 priority, to ensure that they are being run before any other watchers
1586 after the poll. Also, <code>ev_check</code> watchers (and <code>ev_prepare</code> watchers,
1587 too) should not activate (&quot;feed&quot;) events into libev. While libev fully
1588 supports this, they will be called before other <code>ev_check</code> watchers did
1589 their job. As <code>ev_check</code> watchers are often used to embed other event
1590 loops those other event loops might be in an unusable state until their
1591 <code>ev_check</code> watcher ran (always remind yourself to coexist peacefully with
1592 others).</p>
1594 </div>
1595 <h3 id="Watcher_Specific_Functions_and_Data_-8">Watcher-Specific Functions and Data Members</h3>
1596 <div id="Watcher_Specific_Functions_and_Data_-2-6">
1597 <dl>
1598 <dt>ev_prepare_init (ev_prepare *, callback)</dt>
1599 <dt>ev_check_init (ev_check *, callback)</dt>
1600 <dd>
1601 <p>Initialises and configures the prepare or check watcher - they have no
1602 parameters of any kind. There are <code>ev_prepare_set</code> and <code>ev_check_set</code>
1603 macros, but using them is utterly, utterly and completely pointless.</p>
1604 </dd>
1605 </dl>
1606 <p>There are a number of principal ways to embed other event loops or modules
1607 into libev. Here are some ideas on how to include libadns into libev
1608 (there is a Perl module named <code>EV::ADNS</code> that does this, which you could
1609 use for an actually working example. Another Perl module named <code>EV::Glib</code>
1610 embeds a Glib main context into libev, and finally, <code>Glib::EV</code> embeds EV
1611 into the Glib event loop).</p>
1612 <p>Method 1: Add IO watchers and a timeout watcher in a prepare handler,
1613 and in a check watcher, destroy them and call into libadns. What follows
1614 is pseudo-code only of course. This requires you to either use a low
1615 priority for the check watcher or use <code>ev_clear_pending</code> explicitly, as
1616 the callbacks for the IO/timeout watchers might not have been called yet.</p>
1617 <pre> static ev_io iow [nfd];
1618 static ev_timer tw;
1620 static void
1621 io_cb (ev_loop *loop, ev_io *w, int revents)
1622 {
1623 }
1625 // create io watchers for each fd and a timer before blocking
1626 static void
1627 adns_prepare_cb (ev_loop *loop, ev_prepare *w, int revents)
1628 {
1629 int timeout = 3600000;
1630 struct pollfd fds [nfd];
1631 // actual code will need to loop here and realloc etc.
1632 adns_beforepoll (ads, fds, &amp;nfd, &amp;timeout, timeval_from (ev_time ()));
1634 /* the callback is illegal, but won't be called as we stop during check */
1635 ev_timer_init (&amp;tw, 0, timeout * 1e-3);
1636 ev_timer_start (loop, &amp;tw);
1638 // create one ev_io per pollfd
1639 for (int i = 0; i &lt; nfd; ++i)
1640 {
1641 ev_io_init (iow + i, io_cb, fds [i].fd,
1642 ((fds [i].events &amp; POLLIN ? EV_READ : 0)
1643 | (fds [i].events &amp; POLLOUT ? EV_WRITE : 0)));
1645 fds [i].revents = 0;
1646 ev_io_start (loop, iow + i);
1647 }
1648 }
1650 // stop all watchers after blocking
1651 static void
1652 adns_check_cb (ev_loop *loop, ev_check *w, int revents)
1653 {
1654 ev_timer_stop (loop, &amp;tw);
1656 for (int i = 0; i &lt; nfd; ++i)
1657 {
1658 // set the relevant poll flags
1659 // could also call adns_processreadable etc. here
1660 struct pollfd *fd = fds + i;
1661 int revents = ev_clear_pending (iow + i);
1662 if (revents &amp; EV_READ ) fd-&gt;revents |= fd-&gt;events &amp; POLLIN;
1663 if (revents &amp; EV_WRITE) fd-&gt;revents |= fd-&gt;events &amp; POLLOUT;
1665 // now stop the watcher
1666 ev_io_stop (loop, iow + i);
1667 }
1669 adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
1670 }
1672 </pre>
1673 <p>Method 2: This would be just like method 1, but you run <code>adns_afterpoll</code>
1674 in the prepare watcher and would dispose of the check watcher.</p>
1675 <p>Method 3: If the module to be embedded supports explicit event
1676 notification (adns does), you can also make use of the actual watcher
1677 callbacks, and only destroy/create the watchers in the prepare watcher.</p>
1678 <pre> static void
1679 timer_cb (EV_P_ ev_timer *w, int revents)
1680 {
1681 adns_state ads = (adns_state)w-&gt;data;
1682 update_now (EV_A);
1684 adns_processtimeouts (ads, &amp;tv_now);
1685 }
1687 static void
1688 io_cb (EV_P_ ev_io *w, int revents)
1689 {
1690 adns_state ads = (adns_state)w-&gt;data;
1691 update_now (EV_A);
1693 if (revents &amp; EV_READ ) adns_processreadable (ads, w-&gt;fd, &amp;tv_now);
1694 if (revents &amp; EV_WRITE) adns_processwriteable (ads, w-&gt;fd, &amp;tv_now);
1695 }
1697 // do not ever call adns_afterpoll
1699 </pre>
1700 <p>Method 4: Do not use a prepare or check watcher because the module you
1701 want to embed is too inflexible to support it. Instead, youc na override
1702 their poll function. The drawback with this solution is that the main
1703 loop is now no longer controllable by EV. The <code>Glib::EV</code> module does
1704 this.</p>
1705 <pre> static gint
1706 event_poll_func (GPollFD *fds, guint nfds, gint timeout)
1707 {
1708 int got_events = 0;
1710 for (n = 0; n &lt; nfds; ++n)
1711 // create/start io watcher that sets the relevant bits in fds[n] and increment got_events
1713 if (timeout &gt;= 0)
1714 // create/start timer
1716 // poll
1717 ev_loop (EV_A_ 0);
1719 // stop timer again
1720 if (timeout &gt;= 0)
1721 ev_timer_stop (EV_A_ &amp;to);
1723 // stop io watchers again - their callbacks should have set
1724 for (n = 0; n &lt; nfds; ++n)
1725 ev_io_stop (EV_A_ iow [n]);
1727 return got_events;
1728 }
1733 </pre>
1735 </div>
1736 <h2 id="code_ev_embed_code_when_one_backend_"><code>ev_embed</code> - when one backend isn't enough...</h2>
1737 <div id="code_ev_embed_code_when_one_backend_-2">
1738 <p>This is a rather advanced watcher type that lets you embed one event loop
1739 into another (currently only <code>ev_io</code> events are supported in the embedded
1740 loop, other types of watchers might be handled in a delayed or incorrect
1741 fashion and must not be used).</p>
1742 <p>There are primarily two reasons you would want that: work around bugs and
1743 prioritise I/O.</p>
1744 <p>As an example for a bug workaround, the kqueue backend might only support
1745 sockets on some platform, so it is unusable as generic backend, but you
1746 still want to make use of it because you have many sockets and it scales
1747 so nicely. In this case, you would create a kqueue-based loop and embed it
1748 into your default loop (which might use e.g. poll). Overall operation will
1749 be a bit slower because first libev has to poll and then call kevent, but
1750 at least you can use both at what they are best.</p>
1751 <p>As for prioritising I/O: rarely you have the case where some fds have
1752 to be watched and handled very quickly (with low latency), and even
1753 priorities and idle watchers might have too much overhead. In this case
1754 you would put all the high priority stuff in one loop and all the rest in
1755 a second one, and embed the second one in the first.</p>
1756 <p>As long as the watcher is active, the callback will be invoked every time
1757 there might be events pending in the embedded loop. The callback must then
1758 call <code>ev_embed_sweep (mainloop, watcher)</code> to make a single sweep and invoke
1759 their callbacks (you could also start an idle watcher to give the embedded
1760 loop strictly lower priority for example). You can also set the callback
1761 to <code>0</code>, in which case the embed watcher will automatically execute the
1762 embedded loop sweep.</p>
1763 <p>As long as the watcher is started it will automatically handle events. The
1764 callback will be invoked whenever some events have been handled. You can
1765 set the callback to <code>0</code> to avoid having to specify one if you are not
1766 interested in that.</p>
1767 <p>Also, there have not currently been made special provisions for forking:
1768 when you fork, you not only have to call <code>ev_loop_fork</code> on both loops,
1769 but you will also have to stop and restart any <code>ev_embed</code> watchers
1770 yourself.</p>
1771 <p>Unfortunately, not all backends are embeddable, only the ones returned by
1772 <code>ev_embeddable_backends</code> are, which, unfortunately, does not include any
1773 portable one.</p>
1774 <p>So when you want to use this feature you will always have to be prepared
1775 that you cannot get an embeddable loop. The recommended way to get around
1776 this is to have a separate variables for your embeddable loop, try to
1777 create it, and if that fails, use the normal loop for everything:</p>
1778 <pre> struct ev_loop *loop_hi = ev_default_init (0);
1779 struct ev_loop *loop_lo = 0;
1780 struct ev_embed embed;
1782 // see if there is a chance of getting one that works
1783 // (remember that a flags value of 0 means autodetection)
1784 loop_lo = ev_embeddable_backends () &amp; ev_recommended_backends ()
1785 ? ev_loop_new (ev_embeddable_backends () &amp; ev_recommended_backends ())
1786 : 0;
1788 // if we got one, then embed it, otherwise default to loop_hi
1789 if (loop_lo)
1790 {
1791 ev_embed_init (&amp;embed, 0, loop_lo);
1792 ev_embed_start (loop_hi, &amp;embed);
1793 }
1794 else
1795 loop_lo = loop_hi;
1797 </pre>
1799 </div>
1800 <h3 id="Watcher_Specific_Functions_and_Data_-9">Watcher-Specific Functions and Data Members</h3>
1801 <div id="Watcher_Specific_Functions_and_Data_-2-7">
1802 <dl>
1803 <dt>ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)</dt>
1804 <dt>ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)</dt>
1805 <dd>
1806 <p>Configures the watcher to embed the given loop, which must be
1807 embeddable. If the callback is <code>0</code>, then <code>ev_embed_sweep</code> will be
1808 invoked automatically, otherwise it is the responsibility of the callback
1809 to invoke it (it will continue to be called until the sweep has been done,
1810 if you do not want thta, you need to temporarily stop the embed watcher).</p>
1811 </dd>
1812 <dt>ev_embed_sweep (loop, ev_embed *)</dt>
1813 <dd>
1814 <p>Make a single, non-blocking sweep over the embedded loop. This works
1815 similarly to <code>ev_loop (embedded_loop, EVLOOP_NONBLOCK)</code>, but in the most
1816 apropriate way for embedded loops.</p>
1817 </dd>
1818 <dt>struct ev_loop *loop [read-only]</dt>
1819 <dd>
1820 <p>The embedded event loop.</p>
1821 </dd>
1822 </dl>
1828 </div>
1829 <h2 id="code_ev_fork_code_the_audacity_to_re"><code>ev_fork</code> - the audacity to resume the event loop after a fork</h2>
1830 <div id="code_ev_fork_code_the_audacity_to_re-2">
1831 <p>Fork watchers are called when a <code>fork ()</code> was detected (usually because
1832 whoever is a good citizen cared to tell libev about it by calling
1833 <code>ev_default_fork</code> or <code>ev_loop_fork</code>). The invocation is done before the
1834 event loop blocks next and before <code>ev_check</code> watchers are being called,
1835 and only in the child after the fork. If whoever good citizen calling
1836 <code>ev_default_fork</code> cheats and calls it in the wrong process, the fork
1837 handlers will be invoked, too, of course.</p>
1839 </div>
1840 <h3 id="Watcher_Specific_Functions_and_Data_-10">Watcher-Specific Functions and Data Members</h3>
1841 <div id="Watcher_Specific_Functions_and_Data_-2-8">
1842 <dl>
1843 <dt>ev_fork_init (ev_signal *, callback)</dt>
1844 <dd>
1845 <p>Initialises and configures the fork watcher - it has no parameters of any
1846 kind. There is a <code>ev_fork_set</code> macro, but using it is utterly pointless,
1847 believe me.</p>
1848 </dd>
1849 </dl>
1855 </div>
1858 <p>There are some other functions of possible interest. Described. Here. Now.</p>
1859 <dl>
1860 <dt>ev_once (loop, int fd, int events, ev_tstamp timeout, callback)</dt>
1861 <dd>
1862 <p>This function combines a simple timer and an I/O watcher, calls your
1863 callback on whichever event happens first and automatically stop both
1864 watchers. This is useful if you want to wait for a single event on an fd
1865 or timeout without having to allocate/configure/start/stop/free one or
1866 more watchers yourself.</p>
1867 <p>If <code>fd</code> is less than 0, then no I/O watcher will be started and events
1868 is being ignored. Otherwise, an <code>ev_io</code> watcher for the given <code>fd</code> and
1869 <code>events</code> set will be craeted and started.</p>
1870 <p>If <code>timeout</code> is less than 0, then no timeout watcher will be
1871 started. Otherwise an <code>ev_timer</code> watcher with after = <code>timeout</code> (and
1872 repeat = 0) will be started. While <code>0</code> is a valid timeout, it is of
1873 dubious value.</p>
1874 <p>The callback has the type <code>void (*cb)(int revents, void *arg)</code> and gets
1875 passed an <code>revents</code> set like normal event callbacks (a combination of
1876 <code>EV_ERROR</code>, <code>EV_READ</code>, <code>EV_WRITE</code> or <code>EV_TIMEOUT</code>) and the <code>arg</code>
1877 value passed to <code>ev_once</code>:</p>
1878 <pre> static void stdin_ready (int revents, void *arg)
1879 {
1880 if (revents &amp; EV_TIMEOUT)
1881 /* doh, nothing entered */;
1882 else if (revents &amp; EV_READ)
1883 /* stdin might have data for us, joy! */;
1884 }
1886 ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
1888 </pre>
1889 </dd>
1890 <dt>ev_feed_event (ev_loop *, watcher *, int revents)</dt>
1891 <dd>
1892 <p>Feeds the given event set into the event loop, as if the specified event
1893 had happened for the specified watcher (which must be a pointer to an
1894 initialised but not necessarily started event watcher).</p>
1895 </dd>
1896 <dt>ev_feed_fd_event (ev_loop *, int fd, int revents)</dt>
1897 <dd>
1898 <p>Feed an event on the given fd, as if a file descriptor backend detected
1899 the given events it.</p>
1900 </dd>
1901 <dt>ev_feed_signal_event (ev_loop *loop, int signum)</dt>
1902 <dd>
1903 <p>Feed an event as if the given signal occured (<code>loop</code> must be the default
1904 loop!).</p>
1905 </dd>
1906 </dl>
1912 </div>
1915 <p>Libev offers a compatibility emulation layer for libevent. It cannot
1916 emulate the internals of libevent, so here are some usage hints:</p>
1917 <dl>
1918 <dt>* Use it by including &lt;event.h&gt;, as usual.</dt>
1919 <dt>* The following members are fully supported: ev_base, ev_callback,
1920 ev_arg, ev_fd, ev_res, ev_events.</dt>
1921 <dt>* Avoid using ev_flags and the EVLIST_*-macros, while it is
1922 maintained by libev, it does not work exactly the same way as in libevent (consider
1923 it a private API).</dt>
1924 <dt>* Priorities are not currently supported. Initialising priorities
1925 will fail and all watchers will have the same priority, even though there
1926 is an ev_pri field.</dt>
1927 <dt>* Other members are not supported.</dt>
1928 <dt>* The libev emulation is <i>not</i> ABI compatible to libevent, you need
1929 to use the libev header file and library.</dt>
1930 </dl>
1932 </div>
1933 <h1 id="C_SUPPORT">C++ SUPPORT</h1>
1934 <div id="C_SUPPORT_CONTENT">
1935 <p>Libev comes with some simplistic wrapper classes for C++ that mainly allow
1936 you to use some convinience methods to start/stop watchers and also change
1937 the callback model to a model using method callbacks on objects.</p>
1938 <p>To use it,</p>
1939 <pre> #include &lt;ev++.h&gt;
1941 </pre>
1942 <p>This automatically includes <cite>ev.h</cite> and puts all of its definitions (many
1943 of them macros) into the global namespace. All C++ specific things are
1944 put into the <code>ev</code> namespace. It should support all the same embedding
1945 options as <cite>ev.h</cite>, most notably <code>EV_MULTIPLICITY</code>.</p>
1946 <p>Care has been taken to keep the overhead low. The only data member the C++
1947 classes add (compared to plain C-style watchers) is the event loop pointer
1948 that the watcher is associated with (or no additional members at all if
1949 you disable <code>EV_MULTIPLICITY</code> when embedding libev).</p>
1950 <p>Currently, functions, and static and non-static member functions can be
1951 used as callbacks. Other types should be easy to add as long as they only
1952 need one additional pointer for context. If you need support for other
1953 types of functors please contact the author (preferably after implementing
1954 it).</p>
1955 <p>Here is a list of things available in the <code>ev</code> namespace:</p>
1956 <dl>
1957 <dt><code>ev::READ</code>, <code>ev::WRITE</code> etc.</dt>
1958 <dd>
1959 <p>These are just enum values with the same values as the <code>EV_READ</code> etc.
1960 macros from <cite>ev.h</cite>.</p>
1961 </dd>
1962 <dt><code>ev::tstamp</code>, <code>ev::now</code></dt>
1963 <dd>
1964 <p>Aliases to the same types/functions as with the <code>ev_</code> prefix.</p>
1965 </dd>
1966 <dt><code>ev::io</code>, <code>ev::timer</code>, <code>ev::periodic</code>, <code>ev::idle</code>, <code>ev::sig</code> etc.</dt>
1967 <dd>
1968 <p>For each <code>ev_TYPE</code> watcher in <cite>ev.h</cite> there is a corresponding class of
1969 the same name in the <code>ev</code> namespace, with the exception of <code>ev_signal</code>
1970 which is called <code>ev::sig</code> to avoid clashes with the <code>signal</code> macro
1971 defines by many implementations.</p>
1972 <p>All of those classes have these methods:</p>
1973 <p>
1974 <dl>
1975 <dt>ev::TYPE::TYPE ()</dt>
1976 <dt>ev::TYPE::TYPE (struct ev_loop *)</dt>
1977 <dt>ev::TYPE::~TYPE</dt>
1978 <dd>
1979 <p>The constructor (optionally) takes an event loop to associate the watcher
1980 with. If it is omitted, it will use <code>EV_DEFAULT</code>.</p>
1981 <p>The constructor calls <code>ev_init</code> for you, which means you have to call the
1982 <code>set</code> method before starting it.</p>
1983 <p>It will not set a callback, however: You have to call the templated <code>set</code>
1984 method to set a callback before you can start the watcher.</p>
1985 <p>(The reason why you have to use a method is a limitation in C++ which does
1986 not allow explicit template arguments for constructors).</p>
1987 <p>The destructor automatically stops the watcher if it is active.</p>
1988 </dd>
1989 <dt>w-&gt;set&lt;class, &amp;class::method&gt; (object *)</dt>
1990 <dd>
1991 <p>This method sets the callback method to call. The method has to have a
1992 signature of <code>void (*)(ev_TYPE &amp;, int)</code>, it receives the watcher as
1993 first argument and the <code>revents</code> as second. The object must be given as
1994 parameter and is stored in the <code>data</code> member of the watcher.</p>
1995 <p>This method synthesizes efficient thunking code to call your method from
1996 the C callback that libev requires. If your compiler can inline your
1997 callback (i.e. it is visible to it at the place of the <code>set</code> call and
1998 your compiler is good :), then the method will be fully inlined into the
1999 thunking function, making it as fast as a direct C callback.</p>
2000 <p>Example: simple class declaration and watcher initialisation</p>
2001 <pre> struct myclass
2002 {
2003 void io_cb (ev::io &amp;w, int revents) { }
2004 }
2006 myclass obj;
2007 ev::io iow;
2008 iow.set &lt;myclass, &amp;myclass::io_cb&gt; (&amp;obj);
2010 </pre>
2011 </dd>
2012 <dt>w-&gt;set&lt;function&gt; (void *data = 0)</dt>
2013 <dd>
2014 <p>Also sets a callback, but uses a static method or plain function as
2015 callback. The optional <code>data</code> argument will be stored in the watcher's
2016 <code>data</code> member and is free for you to use.</p>
2017 <p>The prototype of the <code>function</code> must be <code>void (*)(ev::TYPE &amp;w, int)</code>.</p>
2018 <p>See the method-<code>set</code> above for more details.</p>
2019 <p>Example:</p>
2020 <pre> static void io_cb (ev::io &amp;w, int revents) { }
2021 iow.set &lt;io_cb&gt; ();
2023 </pre>
2024 </dd>
2025 <dt>w-&gt;set (struct ev_loop *)</dt>
2026 <dd>
2027 <p>Associates a different <code>struct ev_loop</code> with this watcher. You can only
2028 do this when the watcher is inactive (and not pending either).</p>
2029 </dd>
2030 <dt>w-&gt;set ([args])</dt>
2031 <dd>
2032 <p>Basically the same as <code>ev_TYPE_set</code>, with the same args. Must be
2033 called at least once. Unlike the C counterpart, an active watcher gets
2034 automatically stopped and restarted when reconfiguring it with this
2035 method.</p>
2036 </dd>
2037 <dt>w-&gt;start ()</dt>
2038 <dd>
2039 <p>Starts the watcher. Note that there is no <code>loop</code> argument, as the
2040 constructor already stores the event loop.</p>
2041 </dd>
2042 <dt>w-&gt;stop ()</dt>
2043 <dd>
2044 <p>Stops the watcher if it is active. Again, no <code>loop</code> argument.</p>
2045 </dd>
2046 <dt>w-&gt;again () <code>ev::timer</code>, <code>ev::periodic</code> only</dt>
2047 <dd>
2048 <p>For <code>ev::timer</code> and <code>ev::periodic</code>, this invokes the corresponding
2049 <code>ev_TYPE_again</code> function.</p>
2050 </dd>
2051 <dt>w-&gt;sweep () <code>ev::embed</code> only</dt>
2052 <dd>
2053 <p>Invokes <code>ev_embed_sweep</code>.</p>
2054 </dd>
2055 <dt>w-&gt;update () <code>ev::stat</code> only</dt>
2056 <dd>
2057 <p>Invokes <code>ev_stat_stat</code>.</p>
2058 </dd>
2059 </dl>
2060 </p>
2061 </dd>
2062 </dl>
2063 <p>Example: Define a class with an IO and idle watcher, start one of them in
2064 the constructor.</p>
2065 <pre> class myclass
2066 {
2067 ev_io io; void io_cb (ev::io &amp;w, int revents);
2068 ev_idle idle void idle_cb (ev::idle &amp;w, int revents);
2070 myclass ();
2071 }
2073 myclass::myclass (int fd)
2074 {
2075 io .set &lt;myclass, &amp;myclass::io_cb &gt; (this);
2076 idle.set &lt;myclass, &amp;myclass::idle_cb&gt; (this);
2078 io.start (fd, ev::READ);
2079 }
2084 </pre>
2086 </div>
2087 <h1 id="MACRO_MAGIC">MACRO MAGIC</h1>
2088 <div id="MACRO_MAGIC_CONTENT">
2089 <p>Libev can be compiled with a variety of options, the most fundemantal is
2090 <code>EV_MULTIPLICITY</code>. This option determines whether (most) functions and
2091 callbacks have an initial <code>struct ev_loop *</code> argument.</p>
2092 <p>To make it easier to write programs that cope with either variant, the
2093 following macros are defined:</p>
2094 <dl>
2095 <dt><code>EV_A</code>, <code>EV_A_</code></dt>
2096 <dd>
2097 <p>This provides the loop <i>argument</i> for functions, if one is required (&quot;ev
2098 loop argument&quot;). The <code>EV_A</code> form is used when this is the sole argument,
2099 <code>EV_A_</code> is used when other arguments are following. Example:</p>
2100 <pre> ev_unref (EV_A);
2101 ev_timer_add (EV_A_ watcher);
2102 ev_loop (EV_A_ 0);
2104 </pre>
2105 <p>It assumes the variable <code>loop</code> of type <code>struct ev_loop *</code> is in scope,
2106 which is often provided by the following macro.</p>
2107 </dd>
2108 <dt><code>EV_P</code>, <code>EV_P_</code></dt>
2109 <dd>
2110 <p>This provides the loop <i>parameter</i> for functions, if one is required (&quot;ev
2111 loop parameter&quot;). The <code>EV_P</code> form is used when this is the sole parameter,
2112 <code>EV_P_</code> is used when other parameters are following. Example:</p>
2113 <pre> // this is how ev_unref is being declared
2114 static void ev_unref (EV_P);
2116 // this is how you can declare your typical callback
2117 static void cb (EV_P_ ev_timer *w, int revents)
2119 </pre>
2120 <p>It declares a parameter <code>loop</code> of type <code>struct ev_loop *</code>, quite
2121 suitable for use with <code>EV_A</code>.</p>
2122 </dd>
2123 <dt><code>EV_DEFAULT</code>, <code>EV_DEFAULT_</code></dt>
2124 <dd>
2125 <p>Similar to the other two macros, this gives you the value of the default
2126 loop, if multiple loops are supported (&quot;ev loop default&quot;).</p>
2127 </dd>
2128 </dl>
2129 <p>Example: Declare and initialise a check watcher, utilising the above
2130 macros so it will work regardless of whether multiple loops are supported
2131 or not.</p>
2132 <pre> static void
2133 check_cb (EV_P_ ev_timer *w, int revents)
2134 {
2135 ev_check_stop (EV_A_ w);
2136 }
2138 ev_check check;
2139 ev_check_init (&amp;check, check_cb);
2140 ev_check_start (EV_DEFAULT_ &amp;check);
2141 ev_loop (EV_DEFAULT_ 0);
2143 </pre>
2145 </div>
2146 <h1 id="EMBEDDING">EMBEDDING</h1>
2147 <div id="EMBEDDING_CONTENT">
2148 <p>Libev can (and often is) directly embedded into host
2149 applications. Examples of applications that embed it include the Deliantra
2150 Game Server, the EV perl module, the GNU Virtual Private Ethernet (gvpe)
2151 and rxvt-unicode.</p>
2152 <p>The goal is to enable you to just copy the neecssary files into your
2153 source directory without having to change even a single line in them, so
2154 you can easily upgrade by simply copying (or having a checked-out copy of
2155 libev somewhere in your source tree).</p>
2157 </div>
2158 <h2 id="FILESETS">FILESETS</h2>
2159 <div id="FILESETS_CONTENT">
2160 <p>Depending on what features you need you need to include one or more sets of files
2161 in your app.</p>
2163 </div>
2166 <p>To include only the libev core (all the <code>ev_*</code> functions), with manual
2167 configuration (no autoconf):</p>
2168 <pre> #define EV_STANDALONE 1
2169 #include &quot;ev.c&quot;
2171 </pre>
2172 <p>This will automatically include <cite>ev.h</cite>, too, and should be done in a
2173 single C source file only to provide the function implementations. To use
2174 it, do the same for <cite>ev.h</cite> in all files wishing to use this API (best
2175 done by writing a wrapper around <cite>ev.h</cite> that you can include instead and
2176 where you can put other configuration options):</p>
2177 <pre> #define EV_STANDALONE 1
2178 #include &quot;ev.h&quot;
2180 </pre>
2181 <p>Both header files and implementation files can be compiled with a C++
2182 compiler (at least, thats a stated goal, and breakage will be treated
2183 as a bug).</p>
2184 <p>You need the following files in your source tree, or in a directory
2185 in your include path (e.g. in libev/ when using -Ilibev):</p>
2186 <pre> ev.h
2187 ev.c
2188 ev_vars.h
2189 ev_wrap.h
2191 ev_win32.c required on win32 platforms only
2193 ev_select.c only when select backend is enabled (which is enabled by default)
2194 ev_poll.c only when poll backend is enabled (disabled by default)
2195 ev_epoll.c only when the epoll backend is enabled (disabled by default)
2196 ev_kqueue.c only when the kqueue backend is enabled (disabled by default)
2197 ev_port.c only when the solaris port backend is enabled (disabled by default)
2199 </pre>
2200 <p><cite>ev.c</cite> includes the backend files directly when enabled, so you only need
2201 to compile this single file.</p>
2203 </div>
2206 <p>To include the libevent compatibility API, also include:</p>
2207 <pre> #include &quot;event.c&quot;
2209 </pre>
2210 <p>in the file including <cite>ev.c</cite>, and:</p>
2211 <pre> #include &quot;event.h&quot;
2213 </pre>
2214 <p>in the files that want to use the libevent API. This also includes <cite>ev.h</cite>.</p>
2215 <p>You need the following additional files for this:</p>
2216 <pre> event.h
2217 event.c
2219 </pre>
2221 </div>
2224 <p>Instead of using <code>EV_STANDALONE=1</code> and providing your config in
2225 whatever way you want, you can also <code>m4_include([libev.m4])</code> in your
2226 <cite></cite> and leave <code>EV_STANDALONE</code> undefined. <cite>ev.c</cite> will then
2227 include <cite>config.h</cite> and configure itself accordingly.</p>
2228 <p>For this of course you need the m4 file:</p>
2229 <pre> libev.m4
2231 </pre>
2233 </div>
2236 <p>Libev can be configured via a variety of preprocessor symbols you have to define
2237 before including any of its files. The default is not to build for multiplicity
2238 and only include the select backend.</p>
2239 <dl>
2240 <dt>EV_STANDALONE</dt>
2241 <dd>
2242 <p>Must always be <code>1</code> if you do not use autoconf configuration, which
2243 keeps libev from including <cite>config.h</cite>, and it also defines dummy
2244 implementations for some libevent functions (such as logging, which is not
2245 supported). It will also not define any of the structs usually found in
2246 <cite>event.h</cite> that are not directly supported by the libev core alone.</p>
2247 </dd>
2248 <dt>EV_USE_MONOTONIC</dt>
2249 <dd>
2250 <p>If defined to be <code>1</code>, libev will try to detect the availability of the
2251 monotonic clock option at both compiletime and runtime. Otherwise no use
2252 of the monotonic clock option will be attempted. If you enable this, you
2253 usually have to link against librt or something similar. Enabling it when
2254 the functionality isn't available is safe, though, althoguh you have
2255 to make sure you link against any libraries where the <code>clock_gettime</code>
2256 function is hiding in (often <cite>-lrt</cite>).</p>
2257 </dd>
2258 <dt>EV_USE_REALTIME</dt>
2259 <dd>
2260 <p>If defined to be <code>1</code>, libev will try to detect the availability of the
2261 realtime clock option at compiletime (and assume its availability at
2262 runtime if successful). Otherwise no use of the realtime clock option will
2263 be attempted. This effectively replaces <code>gettimeofday</code> by <code>clock_get
2264 (CLOCK_REALTIME, ...)</code> and will not normally affect correctness. See tzhe note about libraries
2265 in the description of <code>EV_USE_MONOTONIC</code>, though.</p>
2266 </dd>
2267 <dt>EV_USE_SELECT</dt>
2268 <dd>
2269 <p>If undefined or defined to be <code>1</code>, libev will compile in support for the
2270 <code>select</code>(2) backend. No attempt at autodetection will be done: if no
2271 other method takes over, select will be it. Otherwise the select backend
2272 will not be compiled in.</p>
2273 </dd>
2274 <dt>EV_SELECT_USE_FD_SET</dt>
2275 <dd>
2276 <p>If defined to <code>1</code>, then the select backend will use the system <code>fd_set</code>
2277 structure. This is useful if libev doesn't compile due to a missing
2278 <code>NFDBITS</code> or <code>fd_mask</code> definition or it misguesses the bitset layout on
2279 exotic systems. This usually limits the range of file descriptors to some
2280 low limit such as 1024 or might have other limitations (winsocket only
2281 allows 64 sockets). The <code>FD_SETSIZE</code> macro, set before compilation, might
2282 influence the size of the <code>fd_set</code> used.</p>
2283 </dd>
2285 <dd>
2286 <p>When defined to <code>1</code>, the select backend will assume that
2287 select/socket/connect etc. don't understand file descriptors but
2288 wants osf handles on win32 (this is the case when the select to
2289 be used is the winsock select). This means that it will call
2290 <code>_get_osfhandle</code> on the fd to convert it to an OS handle. Otherwise,
2291 it is assumed that all these functions actually work on fds, even
2292 on win32. Should not be defined on non-win32 platforms.</p>
2293 </dd>
2294 <dt>EV_USE_POLL</dt>
2295 <dd>
2296 <p>If defined to be <code>1</code>, libev will compile in support for the <code>poll</code>(2)
2297 backend. Otherwise it will be enabled on non-win32 platforms. It
2298 takes precedence over select.</p>
2299 </dd>
2300 <dt>EV_USE_EPOLL</dt>
2301 <dd>
2302 <p>If defined to be <code>1</code>, libev will compile in support for the Linux
2303 <code>epoll</code>(7) backend. Its availability will be detected at runtime,
2304 otherwise another method will be used as fallback. This is the
2305 preferred backend for GNU/Linux systems.</p>
2306 </dd>
2307 <dt>EV_USE_KQUEUE</dt>
2308 <dd>
2309 <p>If defined to be <code>1</code>, libev will compile in support for the BSD style
2310 <code>kqueue</code>(2) backend. Its actual availability will be detected at runtime,
2311 otherwise another method will be used as fallback. This is the preferred
2312 backend for BSD and BSD-like systems, although on most BSDs kqueue only
2313 supports some types of fds correctly (the only platform we found that
2314 supports ptys for example was NetBSD), so kqueue might be compiled in, but
2315 not be used unless explicitly requested. The best way to use it is to find
2316 out whether kqueue supports your type of fd properly and use an embedded
2317 kqueue loop.</p>
2318 </dd>
2319 <dt>EV_USE_PORT</dt>
2320 <dd>
2321 <p>If defined to be <code>1</code>, libev will compile in support for the Solaris
2322 10 port style backend. Its availability will be detected at runtime,
2323 otherwise another method will be used as fallback. This is the preferred
2324 backend for Solaris 10 systems.</p>
2325 </dd>
2326 <dt>EV_USE_DEVPOLL</dt>
2327 <dd>
2328 <p>reserved for future expansion, works like the USE symbols above.</p>
2329 </dd>
2330 <dt>EV_USE_INOTIFY</dt>
2331 <dd>
2332 <p>If defined to be <code>1</code>, libev will compile in support for the Linux inotify
2333 interface to speed up <code>ev_stat</code> watchers. Its actual availability will
2334 be detected at runtime.</p>
2335 </dd>
2336 <dt>EV_H</dt>
2337 <dd>
2338 <p>The name of the <cite>ev.h</cite> header file used to include it. The default if
2339 undefined is <code>&lt;ev.h&gt;</code> in <cite>event.h</cite> and <code>&quot;ev.h&quot;</code> in <cite>ev.c</cite>. This
2340 can be used to virtually rename the <cite>ev.h</cite> header file in case of conflicts.</p>
2341 </dd>
2342 <dt>EV_CONFIG_H</dt>
2343 <dd>
2344 <p>If <code>EV_STANDALONE</code> isn't <code>1</code>, this variable can be used to override
2345 <cite>ev.c</cite>'s idea of where to find the <cite>config.h</cite> file, similarly to
2346 <code>EV_H</code>, above.</p>
2347 </dd>
2348 <dt>EV_EVENT_H</dt>
2349 <dd>
2350 <p>Similarly to <code>EV_H</code>, this macro can be used to override <cite>event.c</cite>'s idea
2351 of how the <cite>event.h</cite> header can be found.</p>
2352 </dd>
2353 <dt>EV_PROTOTYPES</dt>
2354 <dd>
2355 <p>If defined to be <code>0</code>, then <cite>ev.h</cite> will not define any function
2356 prototypes, but still define all the structs and other symbols. This is
2357 occasionally useful if you want to provide your own wrapper functions
2358 around libev functions.</p>
2359 </dd>
2360 <dt>EV_MULTIPLICITY</dt>
2361 <dd>
2362 <p>If undefined or defined to <code>1</code>, then all event-loop-specific functions
2363 will have the <code>struct ev_loop *</code> as first argument, and you can create
2364 additional independent event loops. Otherwise there will be no support
2365 for multiple event loops and there is no first event loop pointer
2366 argument. Instead, all functions act on the single default loop.</p>
2367 </dd>
2368 <dt>EV_MINPRI</dt>
2369 <dt>EV_MAXPRI</dt>
2370 <dd>
2371 <p>The range of allowed priorities. <code>EV_MINPRI</code> must be smaller or equal to
2372 <code>EV_MAXPRI</code>, but otherwise there are no non-obvious limitations. You can
2373 provide for more priorities by overriding those symbols (usually defined
2374 to be <code>-2</code> and <code>2</code>, respectively).</p>
2375 <p>When doing priority-based operations, libev usually has to linearly search
2376 all the priorities, so having many of them (hundreds) uses a lot of space
2377 and time, so using the defaults of five priorities (-2 .. +2) is usually
2378 fine.</p>
2379 <p>If your embedding app does not need any priorities, defining these both to
2380 <code>0</code> will save some memory and cpu.</p>
2381 </dd>
2382 <dt>EV_PERIODIC_ENABLE</dt>
2383 <dd>
2384 <p>If undefined or defined to be <code>1</code>, then periodic timers are supported. If
2385 defined to be <code>0</code>, then they are not. Disabling them saves a few kB of
2386 code.</p>
2387 </dd>
2388 <dt>EV_IDLE_ENABLE</dt>
2389 <dd>
2390 <p>If undefined or defined to be <code>1</code>, then idle watchers are supported. If
2391 defined to be <code>0</code>, then they are not. Disabling them saves a few kB of
2392 code.</p>
2393 </dd>
2394 <dt>EV_EMBED_ENABLE</dt>
2395 <dd>
2396 <p>If undefined or defined to be <code>1</code>, then embed watchers are supported. If
2397 defined to be <code>0</code>, then they are not.</p>
2398 </dd>
2399 <dt>EV_STAT_ENABLE</dt>
2400 <dd>
2401 <p>If undefined or defined to be <code>1</code>, then stat watchers are supported. If
2402 defined to be <code>0</code>, then they are not.</p>
2403 </dd>
2404 <dt>EV_FORK_ENABLE</dt>
2405 <dd>
2406 <p>If undefined or defined to be <code>1</code>, then fork watchers are supported. If
2407 defined to be <code>0</code>, then they are not.</p>
2408 </dd>
2409 <dt>EV_MINIMAL</dt>
2410 <dd>
2411 <p>If you need to shave off some kilobytes of code at the expense of some
2412 speed, define this symbol to <code>1</code>. Currently only used for gcc to override
2413 some inlining decisions, saves roughly 30% codesize of amd64.</p>
2414 </dd>
2415 <dt>EV_PID_HASHSIZE</dt>
2416 <dd>
2417 <p><code>ev_child</code> watchers use a small hash table to distribute workload by
2418 pid. The default size is <code>16</code> (or <code>1</code> with <code>EV_MINIMAL</code>), usually more
2419 than enough. If you need to manage thousands of children you might want to
2420 increase this value (<i>must</i> be a power of two).</p>
2421 </dd>
2423 <dd>
2424 <p><code>ev_staz</code> watchers use a small hash table to distribute workload by
2425 inotify watch id. The default size is <code>16</code> (or <code>1</code> with <code>EV_MINIMAL</code>),
2426 usually more than enough. If you need to manage thousands of <code>ev_stat</code>
2427 watchers you might want to increase this value (<i>must</i> be a power of
2428 two).</p>
2429 </dd>
2430 <dt>EV_COMMON</dt>
2431 <dd>
2432 <p>By default, all watchers have a <code>void *data</code> member. By redefining
2433 this macro to a something else you can include more and other types of
2434 members. You have to define it each time you include one of the files,
2435 though, and it must be identical each time.</p>
2436 <p>For example, the perl EV module uses something like this:</p>
2437 <pre> #define EV_COMMON \
2438 SV *self; /* contains this struct */ \
2439 SV *cb_sv, *fh /* note no trailing &quot;;&quot; */
2441 </pre>
2442 </dd>
2443 <dt>EV_CB_DECLARE (type)</dt>
2444 <dt>EV_CB_INVOKE (watcher, revents)</dt>
2445 <dt>ev_set_cb (ev, cb)</dt>
2446 <dd>
2447 <p>Can be used to change the callback member declaration in each watcher,
2448 and the way callbacks are invoked and set. Must expand to a struct member
2449 definition and a statement, respectively. See the <cite>ev.v</cite> header file for
2450 their default definitions. One possible use for overriding these is to
2451 avoid the <code>struct ev_loop *</code> as first argument in all cases, or to use
2452 method calls instead of plain function calls in C++.</p>
2454 </div>
2455 <h2 id="EXAMPLES">EXAMPLES</h2>
2456 <div id="EXAMPLES_CONTENT">
2457 <p>For a real-world example of a program the includes libev
2458 verbatim, you can have a look at the EV perl module
2459 (<a href=""></a>). It has the libev files in
2460 the <cite>libev/</cite> subdirectory and includes them in the <cite>EV/EVAPI.h</cite> (public
2461 interface) and <cite>EV.xs</cite> (implementation) files. Only the <cite>EV.xs</cite> file
2462 will be compiled. It is pretty complex because it provides its own header
2463 file.</p>
2464 <p>The usage in rxvt-unicode is simpler. It has a <cite>ev_cpp.h</cite> header file
2465 that everybody includes and which overrides some configure choices:</p>
2466 <pre> #define EV_MINIMAL 1
2467 #define EV_USE_POLL 0
2468 #define EV_MULTIPLICITY 0
2469 #define EV_PERIODIC_ENABLE 0
2470 #define EV_STAT_ENABLE 0
2471 #define EV_FORK_ENABLE 0
2472 #define EV_CONFIG_H &lt;config.h&gt;
2473 #define EV_MINPRI 0
2474 #define EV_MAXPRI 0
2476 #include &quot;ev++.h&quot;
2478 </pre>
2479 <p>And a <cite>ev_cpp.C</cite> implementation file that contains libev proper and is compiled:</p>
2480 <pre> #include &quot;ev_cpp.h&quot;
2481 #include &quot;ev.c&quot;
2486 </pre>
2488 </div>
2491 <p>In this section the complexities of (many of) the algorithms used inside
2492 libev will be explained. For complexity discussions about backends see the
2493 documentation for <code>ev_default_init</code>.</p>
2494 <p>All of the following are about amortised time: If an array needs to be
2495 extended, libev needs to realloc and move the whole array, but this
2496 happens asymptotically never with higher number of elements, so O(1) might
2497 mean it might do a lengthy realloc operation in rare cases, but on average
2498 it is much faster and asymptotically approaches constant time.</p>
2499 <p>
2500 <dl>
2501 <dt>Starting and stopping timer/periodic watchers: O(log skipped_other_timers)</dt>
2502 <dd>
2503 <p>This means that, when you have a watcher that triggers in one hour and
2504 there are 100 watchers that would trigger before that then inserting will
2505 have to skip those 100 watchers.</p>
2506 </dd>
2507 <dt>Changing timer/periodic watchers (by autorepeat, again): O(log skipped_other_timers)</dt>
2508 <dd>
2509 <p>That means that for changing a timer costs less than removing/adding them
2510 as only the relative motion in the event queue has to be paid for.</p>
2511 </dd>
2512 <dt>Starting io/check/prepare/idle/signal/child watchers: O(1)</dt>
2513 <dd>
2514 <p>These just add the watcher into an array or at the head of a list.
2515 =item Stopping check/prepare/idle watchers: O(1)</p>
2516 </dd>
2517 <dt>Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))</dt>
2518 <dd>
2519 <p>These watchers are stored in lists then need to be walked to find the
2520 correct watcher to remove. The lists are usually short (you don't usually
2521 have many watchers waiting for the same fd or signal).</p>
2522 </dd>
2523 <dt>Finding the next timer per loop iteration: O(1)</dt>
2524 <dt>Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)</dt>
2525 <dd>
2526 <p>A change means an I/O watcher gets started or stopped, which requires
2527 libev to recalculate its status (and possibly tell the kernel).</p>
2528 </dd>
2529 <dt>Activating one watcher: O(1)</dt>
2530 <dt>Priority handling: O(number_of_priorities)</dt>
2531 <dd>
2532 <p>Priorities are implemented by allocating some space for each
2533 priority. When doing priority-based operations, libev usually has to
2534 linearly search all the priorities.</p>
2535 </dd>
2536 </dl>
2537 </p>
2543 </div>
2544 <h1 id="AUTHOR">AUTHOR</h1>
2545 <div id="AUTHOR_CONTENT">
2546 <p>Marc Lehmann &lt;;.</p>
2548 </div>
2549 </div></body>
2550 </html>