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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="Sat Nov 24 11:19:13 2007" /> 9 <meta name="created" content="Sat Nov 24 17:31:33 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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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_REPRESENTATION">TIME REPRESENTATION</a></li>
23<li><a href="#GLOBAL_FUNCTIONS">GLOBAL FUNCTIONS</a></li> 23<li><a href="#GLOBAL_FUNCTIONS">GLOBAL FUNCTIONS</a></li>
24<li><a href="#FUNCTIONS_CONTROLLING_THE_EVENT_LOOP">FUNCTIONS CONTROLLING THE EVENT LOOP</a></li> 24<li><a href="#FUNCTIONS_CONTROLLING_THE_EVENT_LOOP">FUNCTIONS CONTROLLING THE EVENT LOOP</a></li>
25<li><a href="#ANATOMY_OF_A_WATCHER">ANATOMY OF A WATCHER</a> 25<li><a href="#ANATOMY_OF_A_WATCHER">ANATOMY OF A WATCHER</a>
26<ul><li><a href="#SUMMARY_OF_GENERIC_WATCHER_FUNCTIONS">SUMMARY OF GENERIC WATCHER FUNCTIONS</a></li> 26<ul><li><a href="#GENERIC_WATCHER_FUNCTIONS">GENERIC WATCHER FUNCTIONS</a></li>
27<li><a href="#ASSOCIATING_CUSTOM_DATA_WITH_A_WATCH">ASSOCIATING CUSTOM DATA WITH A WATCHER</a></li> 27<li><a href="#ASSOCIATING_CUSTOM_DATA_WITH_A_WATCH">ASSOCIATING CUSTOM DATA WITH A WATCHER</a></li>
28</ul> 28</ul>
29</li> 29</li>
30<li><a href="#WATCHER_TYPES">WATCHER TYPES</a> 30<li><a href="#WATCHER_TYPES">WATCHER TYPES</a>
31<ul><li><a href="#code_ev_io_code_is_this_file_descrip"><code>ev_io</code> - is this file descriptor readable or writable</a></li> 31<ul><li><a href="#code_ev_io_code_is_this_file_descrip"><code>ev_io</code> - is this file descriptor readable or writable?</a></li>
32<li><a href="#code_ev_timer_code_relative_and_opti"><code>ev_timer</code> - relative and optionally recurring timeouts</a></li> 32<li><a href="#code_ev_timer_code_relative_and_opti"><code>ev_timer</code> - relative and optionally repeating timeouts</a></li>
33<li><a href="#code_ev_periodic_code_to_cron_or_not"><code>ev_periodic</code> - to cron or not to cron</a></li> 33<li><a href="#code_ev_periodic_code_to_cron_or_not"><code>ev_periodic</code> - to cron or not to cron?</a></li>
34<li><a href="#code_ev_signal_code_signal_me_when_a"><code>ev_signal</code> - signal me when a signal gets signalled</a></li> 34<li><a href="#code_ev_signal_code_signal_me_when_a"><code>ev_signal</code> - signal me when a signal gets signalled!</a></li>
35<li><a href="#code_ev_child_code_wait_for_pid_stat"><code>ev_child</code> - wait for pid status changes</a></li> 35<li><a href="#code_ev_child_code_watch_out_for_pro"><code>ev_child</code> - watch out for process status changes</a></li>
36<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_idle_code_when_you_ve_got_no"><code>ev_idle</code> - when you've got nothing better to do...</a></li>
37<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<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>
38<li><a href="#code_ev_embed_code_when_one_backend_"><code>ev_embed</code> - when one backend isn't enough</a></li> 38<li><a href="#code_ev_embed_code_when_one_backend_"><code>ev_embed</code> - when one backend isn't enough...</a></li>
39</ul> 39</ul>
40</li> 40</li>
41<li><a href="#OTHER_FUNCTIONS">OTHER FUNCTIONS</a></li> 41<li><a href="#OTHER_FUNCTIONS">OTHER FUNCTIONS</a></li>
42<li><a href="#LIBEVENT_EMULATION">LIBEVENT EMULATION</a></li> 42<li><a href="#LIBEVENT_EMULATION">LIBEVENT EMULATION</a></li>
43<li><a href="#C_SUPPORT">C++ SUPPORT</a></li> 43<li><a href="#C_SUPPORT">C++ SUPPORT</a></li>
… …
513 513
514</pre> 514</pre>
515 </dd> 515 </dd>
516</dl> 516</dl>
517 517
518
519
520
521
518</div> 522</div>
519<h1 id="ANATOMY_OF_A_WATCHER">ANATOMY OF A WATCHER</h1><p><a href="#TOP" class="toplink">Top</a></p> 523<h1 id="ANATOMY_OF_A_WATCHER">ANATOMY OF A WATCHER</h1><p><a href="#TOP" class="toplink">Top</a></p>
520<div id="ANATOMY_OF_A_WATCHER_CONTENT"> 524<div id="ANATOMY_OF_A_WATCHER_CONTENT">
521<p>A watcher is a structure that you create and register to record your 525<p>A watcher is a structure that you create and register to record your
522interest in some event. For instance, if you want to wait for STDIN to 526interest in some event. For instance, if you want to wait for STDIN to
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612programs, though, so beware.</p> 616programs, though, so beware.</p>
613 </dd> 617 </dd>
614</dl> 618</dl>
615 619
616</div> 620</div>
617<h2 id="SUMMARY_OF_GENERIC_WATCHER_FUNCTIONS">SUMMARY OF GENERIC WATCHER FUNCTIONS</h2> 621<h2 id="GENERIC_WATCHER_FUNCTIONS">GENERIC WATCHER FUNCTIONS</h2>
618<div id="SUMMARY_OF_GENERIC_WATCHER_FUNCTIONS-2"> 622<div id="GENERIC_WATCHER_FUNCTIONS_CONTENT">
619<p>In the following description, <code>TYPE</code> stands for the watcher type, 623<p>In the following description, <code>TYPE</code> stands for the watcher type,
620e.g. <code>timer</code> for <code>ev_timer</code> watchers and <code>io</code> for <code>ev_io</code> watchers.</p> 624e.g. <code>timer</code> for <code>ev_timer</code> watchers and <code>io</code> for <code>ev_io</code> watchers.</p>
621<dl> 625<dl>
622 <dt><code>ev_init</code> (ev_TYPE *watcher, callback)</dt> 626 <dt><code>ev_init</code> (ev_TYPE *watcher, callback)</dt>
623 <dd> 627 <dd>
… …
627the type-specific <code>ev_TYPE_set</code> macro afterwards to initialise the 631the type-specific <code>ev_TYPE_set</code> macro afterwards to initialise the
628type-specific parts. For each type there is also a <code>ev_TYPE_init</code> macro 632type-specific parts. For each type there is also a <code>ev_TYPE_init</code> macro
629which rolls both calls into one.</p> 633which rolls both calls into one.</p>
630 <p>You can reinitialise a watcher at any time as long as it has been stopped 634 <p>You can reinitialise a watcher at any time as long as it has been stopped
631(or never started) and there are no pending events outstanding.</p> 635(or never started) and there are no pending events outstanding.</p>
632 <p>The callbakc is always of type <code>void (*)(ev_loop *loop, ev_TYPE *watcher, 636 <p>The callback is always of type <code>void (*)(ev_loop *loop, ev_TYPE *watcher,
633int revents)</code>.</p> 637int revents)</code>.</p>
634 </dd> 638 </dd>
635 <dt><code>ev_TYPE_set</code> (ev_TYPE *, [args])</dt> 639 <dt><code>ev_TYPE_set</code> (ev_TYPE *, [args])</dt>
636 <dd> 640 <dd>
637 <p>This macro initialises the type-specific parts of a watcher. You need to 641 <p>This macro initialises the type-specific parts of a watcher. You need to
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734 738
735 739
736 740
737 741
738</div> 742</div>
739<h2 id="code_ev_io_code_is_this_file_descrip"><code>ev_io</code> - is this file descriptor readable or writable</h2> 743<h2 id="code_ev_io_code_is_this_file_descrip"><code>ev_io</code> - is this file descriptor readable or writable?</h2>
740<div id="code_ev_io_code_is_this_file_descrip-2"> 744<div id="code_ev_io_code_is_this_file_descrip-2">
741<p>I/O watchers check whether a file descriptor is readable or writable 745<p>I/O watchers check whether a file descriptor is readable or writable
742in each iteration of the event loop (This behaviour is called 746in each iteration of the event loop, or, more precisely, when reading
743level-triggering because you keep receiving events as long as the 747would not block the process and writing would at least be able to write
744condition persists. Remember you can stop the watcher if you don't want to 748some data. This behaviour is called level-triggering because you keep
745act on the event and neither want to receive future events).</p> 749receiving events as long as the condition persists. Remember you can stop
750the watcher if you don't want to act on the event and neither want to
751receive future events.</p>
746<p>In general you can register as many read and/or write event watchers per 752<p>In general you can register as many read and/or write event watchers per
747fd as you want (as long as you don't confuse yourself). Setting all file 753fd as you want (as long as you don't confuse yourself). Setting all file
748descriptors to non-blocking mode is also usually a good idea (but not 754descriptors to non-blocking mode is also usually a good idea (but not
749required if you know what you are doing).</p> 755required if you know what you are doing).</p>
750<p>You have to be careful with dup'ed file descriptors, though. Some backends 756<p>You have to be careful with dup'ed file descriptors, though. Some backends
751(the linux epoll backend is a notable example) cannot handle dup'ed file 757(the linux epoll backend is a notable example) cannot handle dup'ed file
752descriptors correctly if you register interest in two or more fds pointing 758descriptors correctly if you register interest in two or more fds pointing
753to the same underlying file/socket etc. description (that is, they share 759to the same underlying file/socket/etc. description (that is, they share
754the same underlying &quot;file open&quot;).</p> 760the same underlying &quot;file open&quot;).</p>
755<p>If you must do this, then force the use of a known-to-be-good backend 761<p>If you must do this, then force the use of a known-to-be-good backend
756(at the time of this writing, this includes only <code>EVBACKEND_SELECT</code> and 762(at the time of this writing, this includes only <code>EVBACKEND_SELECT</code> and
757<code>EVBACKEND_POLL</code>).</p> 763<code>EVBACKEND_POLL</code>).</p>
764<p>Another thing you have to watch out for is that it is quite easy to
765receive &quot;spurious&quot; readyness notifications, that is your callback might
766be called with <code>EV_READ</code> but a subsequent <code>read</code>(2) will actually block
767because there is no data. Not only are some backends known to create a
768lot of those (for example solaris ports), it is very easy to get into
769this situation even with a relatively standard program structure. Thus
770it is best to always use non-blocking I/O: An extra <code>read</code>(2) returning
771<code>EAGAIN</code> is far preferable to a program hanging until some data arrives.</p>
772<p>If you cannot run the fd in non-blocking mode (for example you should not
773play around with an Xlib connection), then you have to seperately re-test
774wether a file descriptor is really ready with a known-to-be good interface
775such as poll (fortunately in our Xlib example, Xlib already does this on
776its own, so its quite safe to use).</p>
758<dl> 777<dl>
759 <dt>ev_io_init (ev_io *, callback, int fd, int events)</dt> 778 <dt>ev_io_init (ev_io *, callback, int fd, int events)</dt>
760 <dt>ev_io_set (ev_io *, int fd, int events)</dt> 779 <dt>ev_io_set (ev_io *, int fd, int events)</dt>
761 <dd> 780 <dd>
762 <p>Configures an <code>ev_io</code> watcher. The fd is the file descriptor to rceeive 781 <p>Configures an <code>ev_io</code> watcher. The <code>fd</code> is the file descriptor to
763events for and events is either <code>EV_READ</code>, <code>EV_WRITE</code> or <code>EV_READ | 782rceeive events for and events is either <code>EV_READ</code>, <code>EV_WRITE</code> or
764EV_WRITE</code> to receive the given events.</p> 783<code>EV_READ | EV_WRITE</code> to receive the given events.</p>
765 <p>Please note that most of the more scalable backend mechanisms (for example
766epoll and solaris ports) can result in spurious readyness notifications
767for file descriptors, so you practically need to use non-blocking I/O (and
768treat callback invocation as hint only), or retest separately with a safe
769interface before doing I/O (XLib can do this), or force the use of either
770<code>EVBACKEND_SELECT</code> or <code>EVBACKEND_POLL</code>, which don't suffer from this
771problem. Also note that it is quite easy to have your callback invoked
772when the readyness condition is no longer valid even when employing
773typical ways of handling events, so its a good idea to use non-blocking
774I/O unconditionally.</p>
775 </dd> 784 </dd>
776</dl> 785</dl>
777<p>Example: call <code>stdin_readable_cb</code> when STDIN_FILENO has become, well 786<p>Example: call <code>stdin_readable_cb</code> when STDIN_FILENO has become, well
778readable, but only once. Since it is likely line-buffered, you could 787readable, but only once. Since it is likely line-buffered, you could
779attempt to read a whole line in the callback:</p> 788attempt to read a whole line in the callback:</p>
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795 804
796 805
797</pre> 806</pre>
798 807
799</div> 808</div>
800<h2 id="code_ev_timer_code_relative_and_opti"><code>ev_timer</code> - relative and optionally recurring timeouts</h2> 809<h2 id="code_ev_timer_code_relative_and_opti"><code>ev_timer</code> - relative and optionally repeating timeouts</h2>
801<div id="code_ev_timer_code_relative_and_opti-2"> 810<div id="code_ev_timer_code_relative_and_opti-2">
802<p>Timer watchers are simple relative timers that generate an event after a 811<p>Timer watchers are simple relative timers that generate an event after a
803given time, and optionally repeating in regular intervals after that.</p> 812given time, and optionally repeating in regular intervals after that.</p>
804<p>The timers are based on real time, that is, if you register an event that 813<p>The timers are based on real time, that is, if you register an event that
805times out after an hour and you reset your system clock to last years 814times out after an hour and you reset your system clock to last years
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881 890
882 891
883</pre> 892</pre>
884 893
885</div> 894</div>
886<h2 id="code_ev_periodic_code_to_cron_or_not"><code>ev_periodic</code> - to cron or not to cron</h2> 895<h2 id="code_ev_periodic_code_to_cron_or_not"><code>ev_periodic</code> - to cron or not to cron?</h2>
887<div id="code_ev_periodic_code_to_cron_or_not-2"> 896<div id="code_ev_periodic_code_to_cron_or_not-2">
888<p>Periodic watchers are also timers of a kind, but they are very versatile 897<p>Periodic watchers are also timers of a kind, but they are very versatile
889(and unfortunately a bit complex).</p> 898(and unfortunately a bit complex).</p>
890<p>Unlike <code>ev_timer</code>'s, they are not based on real time (or relative time) 899<p>Unlike <code>ev_timer</code>'s, they are not based on real time (or relative time)
891but on wallclock time (absolute time). You can tell a periodic watcher 900but on wallclock time (absolute time). You can tell a periodic watcher
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1010 1019
1011 1020
1012</pre> 1021</pre>
1013 1022
1014</div> 1023</div>
1015<h2 id="code_ev_signal_code_signal_me_when_a"><code>ev_signal</code> - signal me when a signal gets signalled</h2> 1024<h2 id="code_ev_signal_code_signal_me_when_a"><code>ev_signal</code> - signal me when a signal gets signalled!</h2>
1016<div id="code_ev_signal_code_signal_me_when_a-2"> 1025<div id="code_ev_signal_code_signal_me_when_a-2">
1017<p>Signal watchers will trigger an event when the process receives a specific 1026<p>Signal watchers will trigger an event when the process receives a specific
1018signal one or more times. Even though signals are very asynchronous, libev 1027signal one or more times. Even though signals are very asynchronous, libev
1019will try it's best to deliver signals synchronously, i.e. as part of the 1028will try it's best to deliver signals synchronously, i.e. as part of the
1020normal event processing, like any other event.</p> 1029normal event processing, like any other event.</p>
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1036 1045
1037 1046
1038 1047
1039 1048
1040</div> 1049</div>
1041<h2 id="code_ev_child_code_wait_for_pid_stat"><code>ev_child</code> - wait for pid status changes</h2> 1050<h2 id="code_ev_child_code_watch_out_for_pro"><code>ev_child</code> - watch out for process status changes</h2>
1042<div id="code_ev_child_code_wait_for_pid_stat-2"> 1051<div id="code_ev_child_code_watch_out_for_pro-2">
1043<p>Child watchers trigger when your process receives a SIGCHLD in response to 1052<p>Child watchers trigger when your process receives a SIGCHLD in response to
1044some child status changes (most typically when a child of yours dies).</p> 1053some child status changes (most typically when a child of yours dies).</p>
1045<dl> 1054<dl>
1046 <dt>ev_child_init (ev_child *, callback, int pid)</dt> 1055 <dt>ev_child_init (ev_child *, callback, int pid)</dt>
1047 <dt>ev_child_set (ev_child *, int pid)</dt> 1056 <dt>ev_child_set (ev_child *, int pid)</dt>
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1069 1078
1070 1079
1071</pre> 1080</pre>
1072 1081
1073</div> 1082</div>
1074<h2 id="code_ev_idle_code_when_you_ve_got_no"><code>ev_idle</code> - when you've got nothing better to do</h2> 1083<h2 id="code_ev_idle_code_when_you_ve_got_no"><code>ev_idle</code> - when you've got nothing better to do...</h2>
1075<div id="code_ev_idle_code_when_you_ve_got_no-2"> 1084<div id="code_ev_idle_code_when_you_ve_got_no-2">
1076<p>Idle watchers trigger events when there are no other events are pending 1085<p>Idle watchers trigger events when there are no other events are pending
1077(prepare, check and other idle watchers do not count). That is, as long 1086(prepare, check and other idle watchers do not count). That is, as long
1078as your process is busy handling sockets or timeouts (or even signals, 1087as your process is busy handling sockets or timeouts (or even signals,
1079imagine) it will not be triggered. But when your process is idle all idle 1088imagine) it will not be triggered. But when your process is idle all idle
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1112 1121
1113 1122
1114</pre> 1123</pre>
1115 1124
1116</div> 1125</div>
1117<h2 id="code_ev_prepare_code_and_code_ev_che"><code>ev_prepare</code> and <code>ev_check</code> - customise your event loop</h2> 1126<h2 id="code_ev_prepare_code_and_code_ev_che"><code>ev_prepare</code> and <code>ev_check</code> - customise your event loop!</h2>
1118<div id="code_ev_prepare_code_and_code_ev_che-2"> 1127<div id="code_ev_prepare_code_and_code_ev_che-2">
1119<p>Prepare and check watchers are usually (but not always) used in tandem: 1128<p>Prepare and check watchers are usually (but not always) used in tandem:
1120prepare watchers get invoked before the process blocks and check watchers 1129prepare watchers get invoked before the process blocks and check watchers
1121afterwards.</p> 1130afterwards.</p>
1122<p>Their main purpose is to integrate other event mechanisms into libev and 1131<p>Their main purpose is to integrate other event mechanisms into libev and
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1153 1162
1154 1163
1155 1164
1156 1165
1157</div> 1166</div>
1158<h2 id="code_ev_embed_code_when_one_backend_"><code>ev_embed</code> - when one backend isn't enough</h2> 1167<h2 id="code_ev_embed_code_when_one_backend_"><code>ev_embed</code> - when one backend isn't enough...</h2>
1159<div id="code_ev_embed_code_when_one_backend_-2"> 1168<div id="code_ev_embed_code_when_one_backend_-2">
1160<p>This is a rather advanced watcher type that lets you embed one event loop 1169<p>This is a rather advanced watcher type that lets you embed one event loop
1161into another (currently only <code>ev_io</code> events are supported in the embedded 1170into another (currently only <code>ev_io</code> events are supported in the embedded
1162loop, other types of watchers might be handled in a delayed or incorrect 1171loop, other types of watchers might be handled in a delayed or incorrect
1163fashion and must not be used).</p> 1172fashion and must not be used).</p>

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