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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 09:57:02 2007" /> 9 <meta name="created" content="Mon Nov 12 20:19:59 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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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_idle_code_when_you_ve_got_no"><code>ev_idle</code> - when you've got nothing better to do</a></li>
36<li><a href="#code_ev_prepare_code_and_code_ev_che"><code>ev_prepare</code> and <code>ev_check</code> - customise your event loop</a></li> 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>
37</ul> 37</ul>
38</li> 38</li>
39<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>
40<li><a href="#AUTHOR">AUTHOR</a> 42<li><a href="#AUTHOR">AUTHOR</a>
41</li> 43</li>
42</ul><hr /> 44</ul><hr />
43<!-- INDEX END --> 45<!-- INDEX END -->
44 46
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99to the double type in C.</p> 101to the double type in C.</p>
100 102
101</div> 103</div>
102<h1 id="GLOBAL_FUNCTIONS">GLOBAL FUNCTIONS</h1><p><a href="#TOP" class="toplink">Top</a></p> 104<h1 id="GLOBAL_FUNCTIONS">GLOBAL FUNCTIONS</h1><p><a href="#TOP" class="toplink">Top</a></p>
103<div id="GLOBAL_FUNCTIONS_CONTENT"> 105<div id="GLOBAL_FUNCTIONS_CONTENT">
106<p>These functions can be called anytime, even before initialising the
107library in any way.</p>
104<dl> 108<dl>
105 <dt>ev_tstamp ev_time ()</dt> 109 <dt>ev_tstamp ev_time ()</dt>
106 <dd> 110 <dd>
107 <p>Returns the current time as libev would use it.</p> 111 <p>Returns the current time as libev would use it.</p>
108 </dd> 112 </dd>
… …
438<p>I/O watchers check whether a file descriptor is readable or writable 442<p>I/O watchers check whether a file descriptor is readable or writable
439in each iteration of the event loop (This behaviour is called 443in each iteration of the event loop (This behaviour is called
440level-triggering because you keep receiving events as long as the 444level-triggering because you keep receiving events as long as the
441condition persists. Remember you can stop the watcher if you don't want to 445condition persists. Remember you can stop the watcher if you don't want to
442act on the event and neither want to receive future events).</p> 446act on the event and neither want to receive future events).</p>
443<p>In general you can register as many read and/or write event watchers oer 447<p>In general you can register as many read and/or write event watchers per
444fd as you want (as long as you don't confuse yourself). Setting all file 448fd as you want (as long as you don't confuse yourself). Setting all file
445descriptors to non-blocking mode is also usually a good idea (but not 449descriptors to non-blocking mode is also usually a good idea (but not
446required if you know what you are doing).</p> 450required if you know what you are doing).</p>
447<p>You have to be careful with dup'ed file descriptors, though. Some backends 451<p>You have to be careful with dup'ed file descriptors, though. Some backends
448(the linux epoll backend is a notable example) cannot handle dup'ed file 452(the linux epoll backend is a notable example) cannot handle dup'ed file
449descriptors correctly if you register interest in two or more fds pointing 453descriptors correctly if you register interest in two or more fds pointing
450to the same file/socket etc. description.</p> 454to the same underlying file/socket etc. description (that is, they share
455the same underlying &quot;file open&quot;).</p>
451<p>If you must do this, then force the use of a known-to-be-good backend 456<p>If you must do this, then force the use of a known-to-be-good backend
452(at the time of this writing, this includes only EVMETHOD_SELECT and 457(at the time of this writing, this includes only EVMETHOD_SELECT and
453EVMETHOD_POLL).</p> 458EVMETHOD_POLL).</p>
454<dl> 459<dl>
455 <dt>ev_io_init (ev_io *, callback, int fd, int events)</dt> 460 <dt>ev_io_init (ev_io *, callback, int fd, int events)</dt>
… …
465<h2 id="code_ev_timer_code_relative_and_opti"><code>ev_timer</code> - relative and optionally recurring timeouts</h2> 470<h2 id="code_ev_timer_code_relative_and_opti"><code>ev_timer</code> - relative and optionally recurring timeouts</h2>
466<div id="code_ev_timer_code_relative_and_opti-2"> 471<div id="code_ev_timer_code_relative_and_opti-2">
467<p>Timer watchers are simple relative timers that generate an event after a 472<p>Timer watchers are simple relative timers that generate an event after a
468given time, and optionally repeating in regular intervals after that.</p> 473given time, and optionally repeating in regular intervals after that.</p>
469<p>The timers are based on real time, that is, if you register an event that 474<p>The timers are based on real time, that is, if you register an event that
470times out after an hour and youreset your system clock to last years 475times out after an hour and you reset your system clock to last years
471time, it will still time out after (roughly) and hour. &quot;Roughly&quot; because 476time, it will still time out after (roughly) and hour. &quot;Roughly&quot; because
472detecting time jumps is hard, and soem inaccuracies are unavoidable (the 477detecting time jumps is hard, and soem inaccuracies are unavoidable (the
473monotonic clock option helps a lot here).</p> 478monotonic clock option helps a lot here).</p>
474<p>The relative timeouts are calculated relative to the <code>ev_now ()</code> 479<p>The relative timeouts are calculated relative to the <code>ev_now ()</code>
475time. This is usually the right thing as this timestamp refers to the time 480time. This is usually the right thing as this timestamp refers to the time
476of the event triggering whatever timeout you are modifying/starting. If 481of the event triggering whatever timeout you are modifying/starting. If
477you suspect event processing to be delayed and you *need* to base the timeout 482you suspect event processing to be delayed and you *need* to base the timeout
478ion the current time, use something like this to adjust for this:</p> 483on the current time, use something like this to adjust for this:</p>
479<pre> ev_timer_set (&amp;timer, after + ev_now () - ev_time (), 0.); 484<pre> ev_timer_set (&amp;timer, after + ev_now () - ev_time (), 0.);
480 485
481</pre> 486</pre>
482<dl> 487<dl>
483 <dt>ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)</dt> 488 <dt>ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)</dt>
… …
488timer will automatically be configured to trigger again <code>repeat</code> seconds 493timer will automatically be configured to trigger again <code>repeat</code> seconds
489later, again, and again, until stopped manually.</p> 494later, again, and again, until stopped manually.</p>
490 <p>The timer itself will do a best-effort at avoiding drift, that is, if you 495 <p>The timer itself will do a best-effort at avoiding drift, that is, if you
491configure a timer to trigger every 10 seconds, then it will trigger at 496configure a timer to trigger every 10 seconds, then it will trigger at
492exactly 10 second intervals. If, however, your program cannot keep up with 497exactly 10 second intervals. If, however, your program cannot keep up with
493the timer (ecause it takes longer than those 10 seconds to do stuff) the 498the timer (because it takes longer than those 10 seconds to do stuff) the
494timer will not fire more than once per event loop iteration.</p> 499timer will not fire more than once per event loop iteration.</p>
495 </dd> 500 </dd>
496 <dt>ev_timer_again (loop)</dt> 501 <dt>ev_timer_again (loop)</dt>
497 <dd> 502 <dd>
498 <p>This will act as if the timer timed out and restart it again if it is 503 <p>This will act as if the timer timed out and restart it again if it is
… …
567 <dd> 572 <dd>
568 <p>In this mode the values for <code>interval</code> and <code>at</code> are both being 573 <p>In this mode the values for <code>interval</code> and <code>at</code> are both being
569ignored. Instead, each time the periodic watcher gets scheduled, the 574ignored. Instead, each time the periodic watcher gets scheduled, the
570reschedule callback will be called with the watcher as first, and the 575reschedule callback will be called with the watcher as first, and the
571current time as second argument.</p> 576current time as second argument.</p>
572 <p>NOTE: <i>This callback MUST NOT stop or destroy the periodic or any other 577 <p>NOTE: <i>This callback MUST NOT stop or destroy any periodic watcher,
573periodic watcher, ever, or make any event loop modifications</i>. If you need 578ever, or make any event loop modifications</i>. If you need to stop it,
574to stop it, return <code>now + 1e30</code> (or so, fudge fudge) and stop it afterwards.</p> 579return <code>now + 1e30</code> (or so, fudge fudge) and stop it afterwards (e.g. by
575 <p>Also, <i>this callback must always return a time that is later than the 580starting a prepare watcher).</p>
576passed <code>now</code> value</i>. Not even <code>now</code> itself will be ok.</p>
577 <p>Its prototype is <code>ev_tstamp (*reschedule_cb)(struct ev_periodic *w, 581 <p>Its prototype is <code>ev_tstamp (*reschedule_cb)(struct ev_periodic *w,
578ev_tstamp now)</code>, e.g.:</p> 582ev_tstamp now)</code>, e.g.:</p>
579<pre> static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now) 583<pre> static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)
580 { 584 {
581 return now + 60.; 585 return now + 60.;
… …
584</pre> 588</pre>
585 <p>It must return the next time to trigger, based on the passed time value 589 <p>It must return the next time to trigger, based on the passed time value
586(that is, the lowest time value larger than to the second argument). It 590(that is, the lowest time value larger than to the second argument). It
587will usually be called just before the callback will be triggered, but 591will usually be called just before the callback will be triggered, but
588might be called at other times, too.</p> 592might be called at other times, too.</p>
593 <p>NOTE: <i>This callback must always return a time that is later than the
594passed <code>now</code> value</i>. Not even <code>now</code> itself will do, it <i>must</i> be larger.</p>
589 <p>This can be used to create very complex timers, such as a timer that 595 <p>This can be used to create very complex timers, such as a timer that
590triggers on each midnight, local time. To do this, you would calculate the 596triggers on each midnight, local time. To do this, you would calculate the
591next midnight after <code>now</code> and return the timestamp value for this. How you do this 597next midnight after <code>now</code> and return the timestamp value for this. How
592is, again, up to you (but it is not trivial).</p> 598you do this is, again, up to you (but it is not trivial, which is the main
599reason I omitted it as an example).</p>
593 </dd> 600 </dd>
594 </dl> 601 </dl>
595 </p> 602 </p>
596 </dd> 603 </dd>
597 <dt>ev_periodic_again (loop, ev_periodic *)</dt> 604 <dt>ev_periodic_again (loop, ev_periodic *)</dt>
… …
670 677
671</div> 678</div>
672<h2 id="code_ev_prepare_code_and_code_ev_che"><code>ev_prepare</code> and <code>ev_check</code> - customise your event loop</h2> 679<h2 id="code_ev_prepare_code_and_code_ev_che"><code>ev_prepare</code> and <code>ev_check</code> - customise your event loop</h2>
673<div id="code_ev_prepare_code_and_code_ev_che-2"> 680<div id="code_ev_prepare_code_and_code_ev_che-2">
674<p>Prepare and check watchers are usually (but not always) used in tandem: 681<p>Prepare and check watchers are usually (but not always) used in tandem:
675Prepare watchers get invoked before the process blocks and check watchers 682prepare watchers get invoked before the process blocks and check watchers
676afterwards.</p> 683afterwards.</p>
677<p>Their main purpose is to integrate other event mechanisms into libev. This 684<p>Their main purpose is to integrate other event mechanisms into libev. This
678could be used, for example, to track variable changes, implement your own 685could be used, for example, to track variable changes, implement your own
679watchers, integrate net-snmp or a coroutine library and lots more.</p> 686watchers, integrate net-snmp or a coroutine library and lots more.</p>
680<p>This is done by examining in each prepare call which file descriptors need 687<p>This is done by examining in each prepare call which file descriptors need
681to be watched by the other library, registering <code>ev_io</code> watchers for 688to be watched by the other library, registering <code>ev_io</code> watchers for
682them and starting an <code>ev_timer</code> watcher for any timeouts (many libraries 689them and starting an <code>ev_timer</code> watcher for any timeouts (many libraries
683provide just this functionality). Then, in the check watcher you check for 690provide just this functionality). Then, in the check watcher you check for
684any events that occured (by checking the pending status of all watchers 691any events that occured (by checking the pending status of all watchers
685and stopping them) and call back into the library. The I/O and timer 692and stopping them) and call back into the library. The I/O and timer
686callbacks will never actually be called (but must be valid neverthelles, 693callbacks will never actually be called (but must be valid nevertheless,
687because you never know, you know?).</p> 694because you never know, you know?).</p>
688<p>As another example, the Perl Coro module uses these hooks to integrate 695<p>As another example, the Perl Coro module uses these hooks to integrate
689coroutines into libev programs, by yielding to other active coroutines 696coroutines into libev programs, by yielding to other active coroutines
690during each prepare and only letting the process block if no coroutines 697during each prepare and only letting the process block if no coroutines
691are ready to run (its actually more complicated, it only runs coroutines 698are ready to run (it's actually more complicated: it only runs coroutines
692with priority higher than the event loop and one lower priority once, 699with priority higher than or equal to the event loop and one coroutine
693using idle watchers to keep the event loop from blocking if lower-priority 700of lower priority, but only once, using idle watchers to keep the event
694coroutines exist, thus mapping low-priority coroutines to idle/background 701loop from blocking if lower-priority coroutines are active, thus mapping
695tasks).</p> 702low-priority coroutines to idle/background tasks).</p>
696<dl> 703<dl>
697 <dt>ev_prepare_init (ev_prepare *, callback)</dt> 704 <dt>ev_prepare_init (ev_prepare *, callback)</dt>
698 <dt>ev_check_init (ev_check *, callback)</dt> 705 <dt>ev_check_init (ev_check *, callback)</dt>
699 <dd> 706 <dd>
700 <p>Initialises and configures the prepare or check watcher - they have no 707 <p>Initialises and configures the prepare or check watcher - they have no
… …
711 <dt>ev_once (loop, int fd, int events, ev_tstamp timeout, callback)</dt> 718 <dt>ev_once (loop, int fd, int events, ev_tstamp timeout, callback)</dt>
712 <dd> 719 <dd>
713 <p>This function combines a simple timer and an I/O watcher, calls your 720 <p>This function combines a simple timer and an I/O watcher, calls your
714callback on whichever event happens first and automatically stop both 721callback on whichever event happens first and automatically stop both
715watchers. This is useful if you want to wait for a single event on an fd 722watchers. This is useful if you want to wait for a single event on an fd
716or timeout without havign to allocate/configure/start/stop/free one or 723or timeout without having to allocate/configure/start/stop/free one or
717more watchers yourself.</p> 724more watchers yourself.</p>
718 <p>If <code>fd</code> is less than 0, then no I/O watcher will be started and events 725 <p>If <code>fd</code> is less than 0, then no I/O watcher will be started and events
719is being ignored. Otherwise, an <code>ev_io</code> watcher for the given <code>fd</code> and 726is being ignored. Otherwise, an <code>ev_io</code> watcher for the given <code>fd</code> and
720<code>events</code> set will be craeted and started.</p> 727<code>events</code> set will be craeted and started.</p>
721 <p>If <code>timeout</code> is less than 0, then no timeout watcher will be 728 <p>If <code>timeout</code> is less than 0, then no timeout watcher will be
722started. Otherwise an <code>ev_timer</code> watcher with after = <code>timeout</code> (and 729started. Otherwise an <code>ev_timer</code> watcher with after = <code>timeout</code> (and
723repeat = 0) will be started. While <code>0</code> is a valid timeout, it is of 730repeat = 0) will be started. While <code>0</code> is a valid timeout, it is of
724dubious value.</p> 731dubious value.</p>
725 <p>The callback has the type <code>void (*cb)(int revents, void *arg)</code> and gets 732 <p>The callback has the type <code>void (*cb)(int revents, void *arg)</code> and gets
726passed an events set like normal event callbacks (with a combination of 733passed an <code>revents</code> set like normal event callbacks (a combination of
727<code>EV_ERROR</code>, <code>EV_READ</code>, <code>EV_WRITE</code> or <code>EV_TIMEOUT</code>) and the <code>arg</code> 734<code>EV_ERROR</code>, <code>EV_READ</code>, <code>EV_WRITE</code> or <code>EV_TIMEOUT</code>) and the <code>arg</code>
728value passed to <code>ev_once</code>:</p> 735value passed to <code>ev_once</code>:</p>
729<pre> static void stdin_ready (int revents, void *arg) 736<pre> static void stdin_ready (int revents, void *arg)
730 { 737 {
731 if (revents &amp; EV_TIMEOUT) 738 if (revents &amp; EV_TIMEOUT)
… …
754 <p>Feed an event as if the given signal occured (loop must be the default loop!).</p> 761 <p>Feed an event as if the given signal occured (loop must be the default loop!).</p>
755 </dd> 762 </dd>
756</dl> 763</dl>
757 764
758</div> 765</div>
766<h1 id="LIBEVENT_EMULATION">LIBEVENT EMULATION</h1><p><a href="#TOP" class="toplink">Top</a></p>
767<div id="LIBEVENT_EMULATION_CONTENT">
768<p>Libev offers a compatibility emulation layer for libevent. It cannot
769emulate the internals of libevent, so here are some usage hints:</p>
770<dl>
771 <dt>* Use it by including &lt;event.h&gt;, as usual.</dt>
772 <dt>* The following members are fully supported: ev_base, ev_callback,
773ev_arg, ev_fd, ev_res, ev_events.</dt>
774 <dt>* Avoid using ev_flags and the EVLIST_*-macros, while it is
775maintained by libev, it does not work exactly the same way as in libevent (consider
776it a private API).</dt>
777 <dt>* Priorities are not currently supported. Initialising priorities
778will fail and all watchers will have the same priority, even though there
779is an ev_pri field.</dt>
780 <dt>* Other members are not supported.</dt>
781 <dt>* The libev emulation is <i>not</i> ABI compatible to libevent, you need
782to use the libev header file and library.</dt>
783</dl>
784
785</div>
786<h1 id="C_SUPPORT">C++ SUPPORT</h1><p><a href="#TOP" class="toplink">Top</a></p>
787<div id="C_SUPPORT_CONTENT">
788<p>TBD.</p>
789
790</div>
759<h1 id="AUTHOR">AUTHOR</h1><p><a href="#TOP" class="toplink">Top</a></p> 791<h1 id="AUTHOR">AUTHOR</h1><p><a href="#TOP" class="toplink">Top</a></p>
760<div id="AUTHOR_CONTENT"> 792<div id="AUTHOR_CONTENT">
761<p>Marc Lehmann &lt;libev@schmorp.de&gt;.</p> 793<p>Marc Lehmann &lt;libev@schmorp.de&gt;.</p>
762 794
763</div> 795</div>

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