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4<head> 4<head>
5 <title>libev</title> 5 <title>libev</title>
6 <meta name="description" content="Pod documentation for libev" /> 6 <meta name="description" content="Pod documentation for libev" />
7 <meta name="inputfile" content="&lt;standard input&gt;" /> 7 <meta name="inputfile" content="&lt;standard input&gt;" />
8 <meta name="outputfile" content="&lt;standard output&gt;" /> 8 <meta name="outputfile" content="&lt;standard output&gt;" />
9 <meta name="created" content="Mon Nov 12 09:46:59 2007" /> 9 <meta name="created" content="Thu Nov 22 13:28:34 2007" />
10 <meta name="generator" content="Pod::Xhtml 1.57" /> 10 <meta name="generator" content="Pod::Xhtml 1.57" />
11<link rel="stylesheet" href="http://res.tst.eu/pod.css"/></head> 11<link rel="stylesheet" href="http://res.tst.eu/pod.css"/></head>
12<body> 12<body>
13<div class="pod"> 13<div class="pod">
14<!-- INDEX START --> 14<!-- INDEX START -->
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17<ul><li><a href="#NAME">NAME</a></li> 17<ul><li><a href="#NAME">NAME</a></li>
18<li><a href="#SYNOPSIS">SYNOPSIS</a></li> 18<li><a href="#SYNOPSIS">SYNOPSIS</a></li>
19<li><a href="#DESCRIPTION">DESCRIPTION</a></li> 19<li><a href="#DESCRIPTION">DESCRIPTION</a></li>
20<li><a href="#FEATURES">FEATURES</a></li> 20<li><a href="#FEATURES">FEATURES</a></li>
21<li><a href="#CONVENTIONS">CONVENTIONS</a></li> 21<li><a href="#CONVENTIONS">CONVENTIONS</a></li>
22<li><a href="#TIME_REPRESENTATION">TIME REPRESENTATION</a></li>
22<li><a href="#TIME_AND_OTHER_GLOBAL_FUNCTIONS">TIME AND OTHER GLOBAL FUNCTIONS</a></li> 23<li><a href="#GLOBAL_FUNCTIONS">GLOBAL FUNCTIONS</a></li>
23<li><a href="#FUNCTIONS_CONTROLLING_THE_EVENT_LOOP">FUNCTIONS CONTROLLING THE EVENT LOOP</a></li> 24<li><a href="#FUNCTIONS_CONTROLLING_THE_EVENT_LOOP">FUNCTIONS CONTROLLING THE EVENT LOOP</a></li>
24<li><a href="#ANATOMY_OF_A_WATCHER">ANATOMY OF A WATCHER</a> 25<li><a href="#ANATOMY_OF_A_WATCHER">ANATOMY OF A WATCHER</a>
25<ul><li><a href="#ASSOCIATING_CUSTOM_DATA_WITH_A_WATCH">ASSOCIATING CUSTOM DATA WITH A WATCHER</a></li> 26<ul><li><a href="#ASSOCIATING_CUSTOM_DATA_WITH_A_WATCH">ASSOCIATING CUSTOM DATA WITH A WATCHER</a></li>
26</ul> 27</ul>
27</li> 28</li>
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30<li><a href="#code_ev_timer_code_relative_and_opti"><code>ev_timer</code> - relative and optionally recurring timeouts</a></li> 31<li><a href="#code_ev_timer_code_relative_and_opti"><code>ev_timer</code> - relative and optionally recurring timeouts</a></li>
31<li><a href="#code_ev_periodic_code_to_cron_or_not"><code>ev_periodic</code> - to cron or not to cron</a></li> 32<li><a href="#code_ev_periodic_code_to_cron_or_not"><code>ev_periodic</code> - to cron or not to cron</a></li>
32<li><a href="#code_ev_signal_code_signal_me_when_a"><code>ev_signal</code> - signal me when a signal gets signalled</a></li> 33<li><a href="#code_ev_signal_code_signal_me_when_a"><code>ev_signal</code> - signal me when a signal gets signalled</a></li>
33<li><a href="#code_ev_child_code_wait_for_pid_stat"><code>ev_child</code> - wait for pid status changes</a></li> 34<li><a href="#code_ev_child_code_wait_for_pid_stat"><code>ev_child</code> - wait for pid status changes</a></li>
34<li><a href="#code_ev_idle_code_when_you_ve_got_no"><code>ev_idle</code> - when you've got nothing better to do</a></li> 35<li><a href="#code_ev_idle_code_when_you_ve_got_no"><code>ev_idle</code> - when you've got nothing better to do</a></li>
35<li><a href="#code_ev_prepare_code_and_code_ev_che"><code>ev_prepare</code> and <code>ev_check</code> - your hooks into the event loop</a></li> 36<li><a href="#code_ev_prepare_code_and_code_ev_che"><code>ev_prepare</code> and <code>ev_check</code> - customise your event loop</a></li>
36</ul> 37</ul>
37</li> 38</li>
38<li><a href="#OTHER_FUNCTIONS">OTHER FUNCTIONS</a></li> 39<li><a href="#OTHER_FUNCTIONS">OTHER FUNCTIONS</a></li>
40<li><a href="#LIBEVENT_EMULATION">LIBEVENT EMULATION</a></li>
41<li><a href="#C_SUPPORT">C++ SUPPORT</a></li>
39<li><a href="#AUTHOR">AUTHOR</a> 42<li><a href="#AUTHOR">AUTHOR</a>
40</li> 43</li>
41</ul><hr /> 44</ul><hr />
42<!-- INDEX END --> 45<!-- INDEX END -->
43 46
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87support for multiple event loops, then all functions taking an initial 90support for multiple event loops, then all functions taking an initial
88argument of name <code>loop</code> (which is always of type <code>struct ev_loop *</code>) 91argument of name <code>loop</code> (which is always of type <code>struct ev_loop *</code>)
89will not have this argument.</p> 92will not have this argument.</p>
90 93
91</div> 94</div>
92<h1 id="TIME_AND_OTHER_GLOBAL_FUNCTIONS">TIME AND OTHER GLOBAL FUNCTIONS</h1><p><a href="#TOP" class="toplink">Top</a></p> 95<h1 id="TIME_REPRESENTATION">TIME REPRESENTATION</h1><p><a href="#TOP" class="toplink">Top</a></p>
93<div id="TIME_AND_OTHER_GLOBAL_FUNCTIONS_CONT"> 96<div id="TIME_REPRESENTATION_CONTENT">
94<p>Libev represents time as a single floating point number, representing the 97<p>Libev represents time as a single floating point number, representing the
95(fractional) number of seconds since the (POSIX) epoch (somewhere near 98(fractional) number of seconds since the (POSIX) epoch (somewhere near
96the beginning of 1970, details are complicated, don't ask). This type is 99the beginning of 1970, details are complicated, don't ask). This type is
97called <code>ev_tstamp</code>, which is what you should use too. It usually aliases 100called <code>ev_tstamp</code>, which is what you should use too. It usually aliases
98to the double type in C.</p> 101to the double type in C.</p>
102
103</div>
104<h1 id="GLOBAL_FUNCTIONS">GLOBAL FUNCTIONS</h1><p><a href="#TOP" class="toplink">Top</a></p>
105<div id="GLOBAL_FUNCTIONS_CONTENT">
106<p>These functions can be called anytime, even before initialising the
107library in any way.</p>
99<dl> 108<dl>
100 <dt>ev_tstamp ev_time ()</dt> 109 <dt>ev_tstamp ev_time ()</dt>
101 <dd> 110 <dd>
102 <p>Returns the current time as libev would use it.</p> 111 <p>Returns the current time as libev would use it. Please note that the
112<code>ev_now</code> function is usually faster and also often returns the timestamp
113you actually want to know.</p>
103 </dd> 114 </dd>
104 <dt>int ev_version_major ()</dt> 115 <dt>int ev_version_major ()</dt>
105 <dt>int ev_version_minor ()</dt> 116 <dt>int ev_version_minor ()</dt>
106 <dd> 117 <dd>
107 <p>You can find out the major and minor version numbers of the library 118 <p>You can find out the major and minor version numbers of the library
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142<div id="FUNCTIONS_CONTROLLING_THE_EVENT_LOOP-2"> 153<div id="FUNCTIONS_CONTROLLING_THE_EVENT_LOOP-2">
143<p>An event loop is described by a <code>struct ev_loop *</code>. The library knows two 154<p>An event loop is described by a <code>struct ev_loop *</code>. The library knows two
144types of such loops, the <i>default</i> loop, which supports signals and child 155types of such loops, the <i>default</i> loop, which supports signals and child
145events, and dynamically created loops which do not.</p> 156events, and dynamically created loops which do not.</p>
146<p>If you use threads, a common model is to run the default event loop 157<p>If you use threads, a common model is to run the default event loop
147in your main thread (or in a separate thrad) and for each thread you 158in your main thread (or in a separate thread) and for each thread you
148create, you also create another event loop. Libev itself does no locking 159create, you also create another event loop. Libev itself does no locking
149whatsoever, so if you mix calls to the same event loop in different 160whatsoever, so if you mix calls to the same event loop in different
150threads, make sure you lock (this is usually a bad idea, though, even if 161threads, make sure you lock (this is usually a bad idea, though, even if
151done correctly, because it's hideous and inefficient).</p> 162done correctly, because it's hideous and inefficient).</p>
152<dl> 163<dl>
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175<code>LIBEV_FLAGS</code>. Otherwise (the default), this environment variable will 186<code>LIBEV_FLAGS</code>. Otherwise (the default), this environment variable will
176override the flags completely if it is found in the environment. This is 187override the flags completely if it is found in the environment. This is
177useful to try out specific backends to test their performance, or to work 188useful to try out specific backends to test their performance, or to work
178around bugs.</p> 189around bugs.</p>
179 </dd> 190 </dd>
180 <dt><code>EVMETHOD_SELECT</code> (portable select backend)</dt> 191 <dt><code>EVMETHOD_SELECT</code> (value 1, portable select backend)</dt>
192 <dd>
193 <p>This is your standard select(2) backend. Not <i>completely</i> standard, as
194libev tries to roll its own fd_set with no limits on the number of fds,
195but if that fails, expect a fairly low limit on the number of fds when
196using this backend. It doesn't scale too well (O(highest_fd)), but its usually
197the fastest backend for a low number of fds.</p>
198 </dd>
181 <dt><code>EVMETHOD_POLL</code> (poll backend, available everywhere except on windows)</dt> 199 <dt><code>EVMETHOD_POLL</code> (value 2, poll backend, available everywhere except on windows)</dt>
182 <dt><code>EVMETHOD_EPOLL</code> (linux only)</dt> 200 <dd>
183 <dt><code>EVMETHOD_KQUEUE</code> (some bsds only)</dt> 201 <p>And this is your standard poll(2) backend. It's more complicated than
184 <dt><code>EVMETHOD_DEVPOLL</code> (solaris 8 only)</dt> 202select, but handles sparse fds better and has no artificial limit on the
185 <dt><code>EVMETHOD_PORT</code> (solaris 10 only)</dt> 203number of fds you can use (except it will slow down considerably with a
204lot of inactive fds). It scales similarly to select, i.e. O(total_fds).</p>
186 <dd> 205 </dd>
187 <p>If one or more of these are ored into the flags value, then only these 206 <dt><code>EVMETHOD_EPOLL</code> (value 4, Linux)</dt>
188backends will be tried (in the reverse order as given here). If one are 207 <dd>
189specified, any backend will do.</p> 208 <p>For few fds, this backend is a bit little slower than poll and select,
209but it scales phenomenally better. While poll and select usually scale like
210O(total_fds) where n is the total number of fds (or the highest fd), epoll scales
211either O(1) or O(active_fds).</p>
212 <p>While stopping and starting an I/O watcher in the same iteration will
213result in some caching, there is still a syscall per such incident
214(because the fd could point to a different file description now), so its
215best to avoid that. Also, dup()ed file descriptors might not work very
216well if you register events for both fds.</p>
217 </dd>
218 <dt><code>EVMETHOD_KQUEUE</code> (value 8, most BSD clones)</dt>
219 <dd>
220 <p>Kqueue deserves special mention, as at the time of this writing, it
221was broken on all BSDs except NetBSD (usually it doesn't work with
222anything but sockets and pipes, except on Darwin, where of course its
223completely useless). For this reason its not being &quot;autodetected&quot; unless
224you explicitly specify the flags (i.e. you don't use EVFLAG_AUTO).</p>
225 <p>It scales in the same way as the epoll backend, but the interface to the
226kernel is more efficient (which says nothing about its actual speed, of
227course). While starting and stopping an I/O watcher does not cause an
228extra syscall as with epoll, it still adds up to four event changes per
229incident, so its best to avoid that.</p>
230 </dd>
231 <dt><code>EVMETHOD_DEVPOLL</code> (value 16, Solaris 8)</dt>
232 <dd>
233 <p>This is not implemented yet (and might never be).</p>
234 </dd>
235 <dt><code>EVMETHOD_PORT</code> (value 32, Solaris 10)</dt>
236 <dd>
237 <p>This uses the Solaris 10 port mechanism. As with everything on Solaris,
238it's really slow, but it still scales very well (O(active_fds)).</p>
239 </dd>
240 <dt><code>EVMETHOD_ALL</code></dt>
241 <dd>
242 <p>Try all backends (even potentially broken ones that wouldn't be tried
243with <code>EVFLAG_AUTO</code>). Since this is a mask, you can do stuff such as
244<code>EVMETHOD_ALL &amp; ~EVMETHOD_KQUEUE</code>.</p>
190 </dd> 245 </dd>
191 </dl> 246 </dl>
192 </p> 247 </p>
248 <p>If one or more of these are ored into the flags value, then only these
249backends will be tried (in the reverse order as given here). If none are
250specified, most compiled-in backend will be tried, usually in reverse
251order of their flag values :)</p>
193 </dd> 252 </dd>
194 <dt>struct ev_loop *ev_loop_new (unsigned int flags)</dt> 253 <dt>struct ev_loop *ev_loop_new (unsigned int flags)</dt>
195 <dd> 254 <dd>
196 <p>Similar to <code>ev_default_loop</code>, but always creates a new event loop that is 255 <p>Similar to <code>ev_default_loop</code>, but always creates a new event loop that is
197always distinct from the default loop. Unlike the default loop, it cannot 256always distinct from the default loop. Unlike the default loop, it cannot
… …
259your process until at least one new event arrives, and will return after 318your process until at least one new event arrives, and will return after
260one iteration of the loop.</p> 319one iteration of the loop.</p>
261 <p>This flags value could be used to implement alternative looping 320 <p>This flags value could be used to implement alternative looping
262constructs, but the <code>prepare</code> and <code>check</code> watchers provide a better and 321constructs, but the <code>prepare</code> and <code>check</code> watchers provide a better and
263more generic mechanism.</p> 322more generic mechanism.</p>
323 <p>Here are the gory details of what ev_loop does:</p>
324<pre> 1. If there are no active watchers (reference count is zero), return.
325 2. Queue and immediately call all prepare watchers.
326 3. If we have been forked, recreate the kernel state.
327 4. Update the kernel state with all outstanding changes.
328 5. Update the &quot;event loop time&quot;.
329 6. Calculate for how long to block.
330 7. Block the process, waiting for events.
331 8. Update the &quot;event loop time&quot; and do time jump handling.
332 9. Queue all outstanding timers.
333 10. Queue all outstanding periodics.
334 11. If no events are pending now, queue all idle watchers.
335 12. Queue all check watchers.
336 13. Call all queued watchers in reverse order (i.e. check watchers first).
337 14. If ev_unloop has been called or EVLOOP_ONESHOT or EVLOOP_NONBLOCK
338 was used, return, otherwise continue with step #1.
339
340</pre>
264 </dd> 341 </dd>
265 <dt>ev_unloop (loop, how)</dt> 342 <dt>ev_unloop (loop, how)</dt>
266 <dd> 343 <dd>
267 <p>Can be used to make a call to <code>ev_loop</code> return early (but only after it 344 <p>Can be used to make a call to <code>ev_loop</code> return early (but only after it
268has processed all outstanding events). The <code>how</code> argument must be either 345has processed all outstanding events). The <code>how</code> argument must be either
269<code>EVUNLOOP_ONCE</code>, which will make the innermost <code>ev_loop</code> call return, or 346<code>EVUNLOOP_ONE</code>, which will make the innermost <code>ev_loop</code> call return, or
270<code>EVUNLOOP_ALL</code>, which will make all nested <code>ev_loop</code> calls return.</p> 347<code>EVUNLOOP_ALL</code>, which will make all nested <code>ev_loop</code> calls return.</p>
271 </dd> 348 </dd>
272 <dt>ev_ref (loop)</dt> 349 <dt>ev_ref (loop)</dt>
273 <dt>ev_unref (loop)</dt> 350 <dt>ev_unref (loop)</dt>
274 <dd> 351 <dd>
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433<p>I/O watchers check whether a file descriptor is readable or writable 510<p>I/O watchers check whether a file descriptor is readable or writable
434in each iteration of the event loop (This behaviour is called 511in each iteration of the event loop (This behaviour is called
435level-triggering because you keep receiving events as long as the 512level-triggering because you keep receiving events as long as the
436condition persists. Remember you can stop the watcher if you don't want to 513condition persists. Remember you can stop the watcher if you don't want to
437act on the event and neither want to receive future events).</p> 514act on the event and neither want to receive future events).</p>
438<p>In general you can register as many read and/or write event watchers oer 515<p>In general you can register as many read and/or write event watchers per
439fd as you want (as long as you don't confuse yourself). Setting all file 516fd as you want (as long as you don't confuse yourself). Setting all file
440descriptors to non-blocking mode is also usually a good idea (but not 517descriptors to non-blocking mode is also usually a good idea (but not
441required if you know what you are doing).</p> 518required if you know what you are doing).</p>
442<p>You have to be careful with dup'ed file descriptors, though. Some backends 519<p>You have to be careful with dup'ed file descriptors, though. Some backends
443(the linux epoll backend is a notable example) cannot handle dup'ed file 520(the linux epoll backend is a notable example) cannot handle dup'ed file
444descriptors correctly if you register interest in two or more fds pointing 521descriptors correctly if you register interest in two or more fds pointing
445to the same file/socket etc. description.</p> 522to the same underlying file/socket etc. description (that is, they share
523the same underlying &quot;file open&quot;).</p>
446<p>If you must do this, then force the use of a known-to-be-good backend 524<p>If you must do this, then force the use of a known-to-be-good backend
447(at the time of this writing, this includes only EVMETHOD_SELECT and 525(at the time of this writing, this includes only EVMETHOD_SELECT and
448EVMETHOD_POLL).</p> 526EVMETHOD_POLL).</p>
449<dl> 527<dl>
450 <dt>ev_io_init (ev_io *, callback, int fd, int events)</dt> 528 <dt>ev_io_init (ev_io *, callback, int fd, int events)</dt>
… …
460<h2 id="code_ev_timer_code_relative_and_opti"><code>ev_timer</code> - relative and optionally recurring timeouts</h2> 538<h2 id="code_ev_timer_code_relative_and_opti"><code>ev_timer</code> - relative and optionally recurring timeouts</h2>
461<div id="code_ev_timer_code_relative_and_opti-2"> 539<div id="code_ev_timer_code_relative_and_opti-2">
462<p>Timer watchers are simple relative timers that generate an event after a 540<p>Timer watchers are simple relative timers that generate an event after a
463given time, and optionally repeating in regular intervals after that.</p> 541given time, and optionally repeating in regular intervals after that.</p>
464<p>The timers are based on real time, that is, if you register an event that 542<p>The timers are based on real time, that is, if you register an event that
465times out after an hour and youreset your system clock to last years 543times out after an hour and you reset your system clock to last years
466time, it will still time out after (roughly) and hour. &quot;Roughly&quot; because 544time, it will still time out after (roughly) and hour. &quot;Roughly&quot; because
467detecting time jumps is hard, and soem inaccuracies are unavoidable (the 545detecting time jumps is hard, and some inaccuracies are unavoidable (the
468monotonic clock option helps a lot here).</p> 546monotonic clock option helps a lot here).</p>
469<p>The relative timeouts are calculated relative to the <code>ev_now ()</code> 547<p>The relative timeouts are calculated relative to the <code>ev_now ()</code>
470time. This is usually the right thing as this timestamp refers to the time 548time. This is usually the right thing as this timestamp refers to the time
471of the event triggering whatever timeout you are modifying/starting. If 549of the event triggering whatever timeout you are modifying/starting. If
472you suspect event processing to be delayed and you *need* to base the timeout 550you suspect event processing to be delayed and you <i>need</i> to base the timeout
473ion the current time, use something like this to adjust for this:</p> 551on the current time, use something like this to adjust for this:</p>
474<pre> ev_timer_set (&amp;timer, after + ev_now () - ev_time (), 0.); 552<pre> ev_timer_set (&amp;timer, after + ev_now () - ev_time (), 0.);
475 553
476</pre> 554</pre>
555<p>The callback is guarenteed to be invoked only when its timeout has passed,
556but if multiple timers become ready during the same loop iteration then
557order of execution is undefined.</p>
477<dl> 558<dl>
478 <dt>ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)</dt> 559 <dt>ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)</dt>
479 <dt>ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)</dt> 560 <dt>ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)</dt>
480 <dd> 561 <dd>
481 <p>Configure the timer to trigger after <code>after</code> seconds. If <code>repeat</code> is 562 <p>Configure the timer to trigger after <code>after</code> seconds. If <code>repeat</code> is
… …
483timer will automatically be configured to trigger again <code>repeat</code> seconds 564timer will automatically be configured to trigger again <code>repeat</code> seconds
484later, again, and again, until stopped manually.</p> 565later, again, and again, until stopped manually.</p>
485 <p>The timer itself will do a best-effort at avoiding drift, that is, if you 566 <p>The timer itself will do a best-effort at avoiding drift, that is, if you
486configure a timer to trigger every 10 seconds, then it will trigger at 567configure a timer to trigger every 10 seconds, then it will trigger at
487exactly 10 second intervals. If, however, your program cannot keep up with 568exactly 10 second intervals. If, however, your program cannot keep up with
488the timer (ecause it takes longer than those 10 seconds to do stuff) the 569the timer (because it takes longer than those 10 seconds to do stuff) the
489timer will not fire more than once per event loop iteration.</p> 570timer will not fire more than once per event loop iteration.</p>
490 </dd> 571 </dd>
491 <dt>ev_timer_again (loop)</dt> 572 <dt>ev_timer_again (loop)</dt>
492 <dd> 573 <dd>
493 <p>This will act as if the timer timed out and restart it again if it is 574 <p>This will act as if the timer timed out and restart it again if it is
… …
519take a year to trigger the event (unlike an <code>ev_timer</code>, which would trigger 600take a year to trigger the event (unlike an <code>ev_timer</code>, which would trigger
520roughly 10 seconds later and of course not if you reset your system time 601roughly 10 seconds later and of course not if you reset your system time
521again).</p> 602again).</p>
522<p>They can also be used to implement vastly more complex timers, such as 603<p>They can also be used to implement vastly more complex timers, such as
523triggering an event on eahc midnight, local time.</p> 604triggering an event on eahc midnight, local time.</p>
605<p>As with timers, the callback is guarenteed to be invoked only when the
606time (<code>at</code>) has been passed, but if multiple periodic timers become ready
607during the same loop iteration then order of execution is undefined.</p>
524<dl> 608<dl>
525 <dt>ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)</dt> 609 <dt>ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)</dt>
526 <dt>ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)</dt> 610 <dt>ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)</dt>
527 <dd> 611 <dd>
528 <p>Lots of arguments, lets sort it out... There are basically three modes of 612 <p>Lots of arguments, lets sort it out... There are basically three modes of
529operation, and we will explain them from simplest to complex:</p> 613operation, and we will explain them from simplest to complex:</p>
530
531
532
533
534 <p> 614 <p>
535 <dl> 615 <dl>
536 <dt>* absolute timer (interval = reschedule_cb = 0)</dt> 616 <dt>* absolute timer (interval = reschedule_cb = 0)</dt>
537 <dd> 617 <dd>
538 <p>In this configuration the watcher triggers an event at the wallclock time 618 <p>In this configuration the watcher triggers an event at the wallclock time
… …
562 <dd> 642 <dd>
563 <p>In this mode the values for <code>interval</code> and <code>at</code> are both being 643 <p>In this mode the values for <code>interval</code> and <code>at</code> are both being
564ignored. Instead, each time the periodic watcher gets scheduled, the 644ignored. Instead, each time the periodic watcher gets scheduled, the
565reschedule callback will be called with the watcher as first, and the 645reschedule callback will be called with the watcher as first, and the
566current time as second argument.</p> 646current time as second argument.</p>
567 <p>NOTE: <i>This callback MUST NOT stop or destroy the periodic or any other 647 <p>NOTE: <i>This callback MUST NOT stop or destroy any periodic watcher,
568periodic watcher, ever, or make any event loop modifications</i>. If you need 648ever, or make any event loop modifications</i>. If you need to stop it,
569to stop it, return <code>now + 1e30</code> (or so, fudge fudge) and stop it afterwards.</p> 649return <code>now + 1e30</code> (or so, fudge fudge) and stop it afterwards (e.g. by
570 <p>Also, <i>this callback must always return a time that is later than the 650starting a prepare watcher).</p>
571passed <code>now</code> value</i>. Not even <code>now</code> itself will be ok.</p>
572 <p>Its prototype is <code>ev_tstamp (*reschedule_cb)(struct ev_periodic *w, 651 <p>Its prototype is <code>ev_tstamp (*reschedule_cb)(struct ev_periodic *w,
573ev_tstamp now)</code>, e.g.:</p> 652ev_tstamp now)</code>, e.g.:</p>
574<pre> static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now) 653<pre> static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)
575 { 654 {
576 return now + 60.; 655 return now + 60.;
… …
579</pre> 658</pre>
580 <p>It must return the next time to trigger, based on the passed time value 659 <p>It must return the next time to trigger, based on the passed time value
581(that is, the lowest time value larger than to the second argument). It 660(that is, the lowest time value larger than to the second argument). It
582will usually be called just before the callback will be triggered, but 661will usually be called just before the callback will be triggered, but
583might be called at other times, too.</p> 662might be called at other times, too.</p>
663 <p>NOTE: <i>This callback must always return a time that is later than the
664passed <code>now</code> value</i>. Not even <code>now</code> itself will do, it <i>must</i> be larger.</p>
584 <p>This can be used to create very complex timers, such as a timer that 665 <p>This can be used to create very complex timers, such as a timer that
585triggers on each midnight, local time. To do this, you would calculate the 666triggers on each midnight, local time. To do this, you would calculate the
586next midnight after <code>now</code> and return the timestamp value for this. How you do this 667next midnight after <code>now</code> and return the timestamp value for this. How
587is, again, up to you (but it is not trivial).</p> 668you do this is, again, up to you (but it is not trivial, which is the main
669reason I omitted it as an example).</p>
588 </dd> 670 </dd>
589 </dl> 671 </dl>
590 </p> 672 </p>
591 </dd> 673 </dd>
592 <dt>ev_periodic_again (loop, ev_periodic *)</dt> 674 <dt>ev_periodic_again (loop, ev_periodic *)</dt>
… …
662believe me.</p> 744believe me.</p>
663 </dd> 745 </dd>
664</dl> 746</dl>
665 747
666</div> 748</div>
667<h2 id="code_ev_prepare_code_and_code_ev_che"><code>ev_prepare</code> and <code>ev_check</code> - your hooks into the event loop</h2> 749<h2 id="code_ev_prepare_code_and_code_ev_che"><code>ev_prepare</code> and <code>ev_check</code> - customise your event loop</h2>
668<div id="code_ev_prepare_code_and_code_ev_che-2"> 750<div id="code_ev_prepare_code_and_code_ev_che-2">
669<p>Prepare and check watchers are usually (but not always) used in tandem: 751<p>Prepare and check watchers are usually (but not always) used in tandem:
670Prepare watchers get invoked before the process blocks and check watchers 752prepare watchers get invoked before the process blocks and check watchers
671afterwards.</p> 753afterwards.</p>
672<p>Their main purpose is to integrate other event mechanisms into libev. This 754<p>Their main purpose is to integrate other event mechanisms into libev. This
673could be used, for example, to track variable changes, implement your own 755could be used, for example, to track variable changes, implement your own
674watchers, integrate net-snmp or a coroutine library and lots more.</p> 756watchers, integrate net-snmp or a coroutine library and lots more.</p>
675<p>This is done by examining in each prepare call which file descriptors need 757<p>This is done by examining in each prepare call which file descriptors need
676to be watched by the other library, registering <code>ev_io</code> watchers for 758to be watched by the other library, registering <code>ev_io</code> watchers for
677them and starting an <code>ev_timer</code> watcher for any timeouts (many libraries 759them and starting an <code>ev_timer</code> watcher for any timeouts (many libraries
678provide just this functionality). Then, in the check watcher you check for 760provide just this functionality). Then, in the check watcher you check for
679any events that occured (by checking the pending status of all watchers 761any events that occured (by checking the pending status of all watchers
680and stopping them) and call back into the library. The I/O and timer 762and stopping them) and call back into the library. The I/O and timer
681callbacks will never actually be called (but must be valid neverthelles, 763callbacks will never actually be called (but must be valid nevertheless,
682because you never know, you know?).</p> 764because you never know, you know?).</p>
683<p>As another example, the Perl Coro module uses these hooks to integrate 765<p>As another example, the Perl Coro module uses these hooks to integrate
684coroutines into libev programs, by yielding to other active coroutines 766coroutines into libev programs, by yielding to other active coroutines
685during each prepare and only letting the process block if no coroutines 767during each prepare and only letting the process block if no coroutines
686are ready to run (its actually more complicated, it only runs coroutines 768are ready to run (it's actually more complicated: it only runs coroutines
687with priority higher than the event loop and one lower priority once, 769with priority higher than or equal to the event loop and one coroutine
688using idle watchers to keep the event loop from blocking if lower-priority 770of lower priority, but only once, using idle watchers to keep the event
689coroutines exist, thus mapping low-priority coroutines to idle/background 771loop from blocking if lower-priority coroutines are active, thus mapping
690tasks).</p> 772low-priority coroutines to idle/background tasks).</p>
691<dl> 773<dl>
692 <dt>ev_prepare_init (ev_prepare *, callback)</dt> 774 <dt>ev_prepare_init (ev_prepare *, callback)</dt>
693 <dt>ev_check_init (ev_check *, callback)</dt> 775 <dt>ev_check_init (ev_check *, callback)</dt>
694 <dd> 776 <dd>
695 <p>Initialises and configures the prepare or check watcher - they have no 777 <p>Initialises and configures the prepare or check watcher - they have no
… …
706 <dt>ev_once (loop, int fd, int events, ev_tstamp timeout, callback)</dt> 788 <dt>ev_once (loop, int fd, int events, ev_tstamp timeout, callback)</dt>
707 <dd> 789 <dd>
708 <p>This function combines a simple timer and an I/O watcher, calls your 790 <p>This function combines a simple timer and an I/O watcher, calls your
709callback on whichever event happens first and automatically stop both 791callback on whichever event happens first and automatically stop both
710watchers. This is useful if you want to wait for a single event on an fd 792watchers. This is useful if you want to wait for a single event on an fd
711or timeout without havign to allocate/configure/start/stop/free one or 793or timeout without having to allocate/configure/start/stop/free one or
712more watchers yourself.</p> 794more watchers yourself.</p>
713 <p>If <code>fd</code> is less than 0, then no I/O watcher will be started and events 795 <p>If <code>fd</code> is less than 0, then no I/O watcher will be started and events
714is being ignored. Otherwise, an <code>ev_io</code> watcher for the given <code>fd</code> and 796is being ignored. Otherwise, an <code>ev_io</code> watcher for the given <code>fd</code> and
715<code>events</code> set will be craeted and started.</p> 797<code>events</code> set will be craeted and started.</p>
716 <p>If <code>timeout</code> is less than 0, then no timeout watcher will be 798 <p>If <code>timeout</code> is less than 0, then no timeout watcher will be
717started. Otherwise an <code>ev_timer</code> watcher with after = <code>timeout</code> (and 799started. Otherwise an <code>ev_timer</code> watcher with after = <code>timeout</code> (and
718repeat = 0) will be started. While <code>0</code> is a valid timeout, it is of 800repeat = 0) will be started. While <code>0</code> is a valid timeout, it is of
719dubious value.</p> 801dubious value.</p>
720 <p>The callback has the type <code>void (*cb)(int revents, void *arg)</code> and gets 802 <p>The callback has the type <code>void (*cb)(int revents, void *arg)</code> and gets
721passed an events set like normal event callbacks (with a combination of 803passed an <code>revents</code> set like normal event callbacks (a combination of
722<code>EV_ERROR</code>, <code>EV_READ</code>, <code>EV_WRITE</code> or <code>EV_TIMEOUT</code>) and the <code>arg</code> 804<code>EV_ERROR</code>, <code>EV_READ</code>, <code>EV_WRITE</code> or <code>EV_TIMEOUT</code>) and the <code>arg</code>
723value passed to <code>ev_once</code>:</p> 805value passed to <code>ev_once</code>:</p>
724<pre> static void stdin_ready (int revents, void *arg) 806<pre> static void stdin_ready (int revents, void *arg)
725 { 807 {
726 if (revents &amp; EV_TIMEOUT) 808 if (revents &amp; EV_TIMEOUT)
… …
749 <p>Feed an event as if the given signal occured (loop must be the default loop!).</p> 831 <p>Feed an event as if the given signal occured (loop must be the default loop!).</p>
750 </dd> 832 </dd>
751</dl> 833</dl>
752 834
753</div> 835</div>
836<h1 id="LIBEVENT_EMULATION">LIBEVENT EMULATION</h1><p><a href="#TOP" class="toplink">Top</a></p>
837<div id="LIBEVENT_EMULATION_CONTENT">
838<p>Libev offers a compatibility emulation layer for libevent. It cannot
839emulate the internals of libevent, so here are some usage hints:</p>
840<dl>
841 <dt>* Use it by including &lt;event.h&gt;, as usual.</dt>
842 <dt>* The following members are fully supported: ev_base, ev_callback,
843ev_arg, ev_fd, ev_res, ev_events.</dt>
844 <dt>* Avoid using ev_flags and the EVLIST_*-macros, while it is
845maintained by libev, it does not work exactly the same way as in libevent (consider
846it a private API).</dt>
847 <dt>* Priorities are not currently supported. Initialising priorities
848will fail and all watchers will have the same priority, even though there
849is an ev_pri field.</dt>
850 <dt>* Other members are not supported.</dt>
851 <dt>* The libev emulation is <i>not</i> ABI compatible to libevent, you need
852to use the libev header file and library.</dt>
853</dl>
854
855</div>
856<h1 id="C_SUPPORT">C++ SUPPORT</h1><p><a href="#TOP" class="toplink">Top</a></p>
857<div id="C_SUPPORT_CONTENT">
858<p>TBD.</p>
859
860</div>
754<h1 id="AUTHOR">AUTHOR</h1><p><a href="#TOP" class="toplink">Top</a></p> 861<h1 id="AUTHOR">AUTHOR</h1><p><a href="#TOP" class="toplink">Top</a></p>
755<div id="AUTHOR_CONTENT"> 862<div id="AUTHOR_CONTENT">
756<p>Marc Lehmann &lt;libev@schmorp.de&gt;.</p> 863<p>Marc Lehmann &lt;libev@schmorp.de&gt;.</p>
757 864
758</div> 865</div>

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