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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 Dec 8 16:30:24 2007" /> 9 <meta name="created" content="Sun Dec 9 20:30:11 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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529one iteration of the loop. This is useful if you are waiting for some 529one iteration of the loop. This is useful if you are waiting for some
530external event in conjunction with something not expressible using other 530external event in conjunction with something not expressible using other
531libev watchers. However, a pair of <code>ev_prepare</code>/<code>ev_check</code> watchers is 531libev watchers. However, a pair of <code>ev_prepare</code>/<code>ev_check</code> watchers is
532usually a better approach for this kind of thing.</p> 532usually a better approach for this kind of thing.</p>
533 <p>Here are the gory details of what <code>ev_loop</code> does:</p> 533 <p>Here are the gory details of what <code>ev_loop</code> does:</p>
534<pre> - Before the first iteration, call any pending watchers.
534<pre> * If there are no active watchers (reference count is zero), return. 535 * If there are no active watchers (reference count is zero), return.
535 - Queue prepare watchers and then call all outstanding watchers. 536 - Queue all prepare watchers and then call all outstanding watchers.
536 - If we have been forked, recreate the kernel state. 537 - If we have been forked, recreate the kernel state.
537 - Update the kernel state with all outstanding changes. 538 - Update the kernel state with all outstanding changes.
538 - Update the &quot;event loop time&quot;. 539 - Update the &quot;event loop time&quot;.
539 - Calculate for how long to block. 540 - Calculate for how long to block.
540 - Block the process, waiting for any events. 541 - Block the process, waiting for any events.
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1096but on wallclock time (absolute time). You can tell a periodic watcher 1097but on wallclock time (absolute time). You can tell a periodic watcher
1097to trigger &quot;at&quot; some specific point in time. For example, if you tell a 1098to trigger &quot;at&quot; some specific point in time. For example, if you tell a
1098periodic watcher to trigger in 10 seconds (by specifiying e.g. <code>ev_now () 1099periodic watcher to trigger in 10 seconds (by specifiying e.g. <code>ev_now ()
1099+ 10.</code>) and then reset your system clock to the last year, then it will 1100+ 10.</code>) and then reset your system clock to the last year, then it will
1100take a year to trigger the event (unlike an <code>ev_timer</code>, which would trigger 1101take a year to trigger the event (unlike an <code>ev_timer</code>, which would trigger
1101roughly 10 seconds later and of course not if you reset your system time 1102roughly 10 seconds later).</p>
1102again).</p>
1103<p>They can also be used to implement vastly more complex timers, such as 1103<p>They can also be used to implement vastly more complex timers, such as
1104triggering an event on eahc midnight, local time.</p> 1104triggering an event on each midnight, local time or other, complicated,
1105rules.</p>
1105<p>As with timers, the callback is guarenteed to be invoked only when the 1106<p>As with timers, the callback is guarenteed to be invoked only when the
1106time (<code>at</code>) has been passed, but if multiple periodic timers become ready 1107time (<code>at</code>) has been passed, but if multiple periodic timers become ready
1107during the same loop iteration then order of execution is undefined.</p> 1108during the same loop iteration then order of execution is undefined.</p>
1108<dl> 1109<dl>
1109 <dt>ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)</dt> 1110 <dt>ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)</dt>
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1111 <dd> 1112 <dd>
1112 <p>Lots of arguments, lets sort it out... There are basically three modes of 1113 <p>Lots of arguments, lets sort it out... There are basically three modes of
1113operation, and we will explain them from simplest to complex:</p> 1114operation, and we will explain them from simplest to complex:</p>
1114 <p> 1115 <p>
1115 <dl> 1116 <dl>
1116 <dt>* absolute timer (interval = reschedule_cb = 0)</dt> 1117 <dt>* absolute timer (at = time, interval = reschedule_cb = 0)</dt>
1117 <dd> 1118 <dd>
1118 <p>In this configuration the watcher triggers an event at the wallclock time 1119 <p>In this configuration the watcher triggers an event at the wallclock time
1119<code>at</code> and doesn't repeat. It will not adjust when a time jump occurs, 1120<code>at</code> and doesn't repeat. It will not adjust when a time jump occurs,
1120that is, if it is to be run at January 1st 2011 then it will run when the 1121that is, if it is to be run at January 1st 2011 then it will run when the
1121system time reaches or surpasses this time.</p> 1122system time reaches or surpasses this time.</p>
1122 </dd> 1123 </dd>
1123 <dt>* non-repeating interval timer (interval &gt; 0, reschedule_cb = 0)</dt> 1124 <dt>* non-repeating interval timer (at = offset, interval &gt; 0, reschedule_cb = 0)</dt>
1124 <dd> 1125 <dd>
1125 <p>In this mode the watcher will always be scheduled to time out at the next 1126 <p>In this mode the watcher will always be scheduled to time out at the next
1126<code>at + N * interval</code> time (for some integer N) and then repeat, regardless 1127<code>at + N * interval</code> time (for some integer N, which can also be negative)
1127of any time jumps.</p> 1128and then repeat, regardless of any time jumps.</p>
1128 <p>This can be used to create timers that do not drift with respect to system 1129 <p>This can be used to create timers that do not drift with respect to system
1129time:</p> 1130time:</p>
1130<pre> ev_periodic_set (&amp;periodic, 0., 3600., 0); 1131<pre> ev_periodic_set (&amp;periodic, 0., 3600., 0);
1131 1132
1132</pre> 1133</pre>
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1135full hour (UTC), or more correctly, when the system time is evenly divisible 1136full hour (UTC), or more correctly, when the system time is evenly divisible
1136by 3600.</p> 1137by 3600.</p>
1137 <p>Another way to think about it (for the mathematically inclined) is that 1138 <p>Another way to think about it (for the mathematically inclined) is that
1138<code>ev_periodic</code> will try to run the callback in this mode at the next possible 1139<code>ev_periodic</code> will try to run the callback in this mode at the next possible
1139time where <code>time = at (mod interval)</code>, regardless of any time jumps.</p> 1140time where <code>time = at (mod interval)</code>, regardless of any time jumps.</p>
1141 <p>For numerical stability it is preferable that the <code>at</code> value is near
1142<code>ev_now ()</code> (the current time), but there is no range requirement for
1143this value.</p>
1140 </dd> 1144 </dd>
1141 <dt>* manual reschedule mode (reschedule_cb = callback)</dt> 1145 <dt>* manual reschedule mode (at and interval ignored, reschedule_cb = callback)</dt>
1142 <dd> 1146 <dd>
1143 <p>In this mode the values for <code>interval</code> and <code>at</code> are both being 1147 <p>In this mode the values for <code>interval</code> and <code>at</code> are both being
1144ignored. Instead, each time the periodic watcher gets scheduled, the 1148ignored. Instead, each time the periodic watcher gets scheduled, the
1145reschedule callback will be called with the watcher as first, and the 1149reschedule callback will be called with the watcher as first, and the
1146current time as second argument.</p> 1150current time as second argument.</p>
1147 <p>NOTE: <i>This callback MUST NOT stop or destroy any periodic watcher, 1151 <p>NOTE: <i>This callback MUST NOT stop or destroy any periodic watcher,
1148ever, or make any event loop modifications</i>. If you need to stop it, 1152ever, or make any event loop modifications</i>. If you need to stop it,
1149return <code>now + 1e30</code> (or so, fudge fudge) and stop it afterwards (e.g. by 1153return <code>now + 1e30</code> (or so, fudge fudge) and stop it afterwards (e.g. by
1150starting a prepare watcher).</p> 1154starting an <code>ev_prepare</code> watcher, which is legal).</p>
1151 <p>Its prototype is <code>ev_tstamp (*reschedule_cb)(struct ev_periodic *w, 1155 <p>Its prototype is <code>ev_tstamp (*reschedule_cb)(struct ev_periodic *w,
1152ev_tstamp now)</code>, e.g.:</p> 1156ev_tstamp now)</code>, e.g.:</p>
1153<pre> static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now) 1157<pre> static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)
1154 { 1158 {
1155 return now + 60.; 1159 return now + 60.;
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1175 <dd> 1179 <dd>
1176 <p>Simply stops and restarts the periodic watcher again. This is only useful 1180 <p>Simply stops and restarts the periodic watcher again. This is only useful
1177when you changed some parameters or the reschedule callback would return 1181when you changed some parameters or the reschedule callback would return
1178a different time than the last time it was called (e.g. in a crond like 1182a different time than the last time it was called (e.g. in a crond like
1179program when the crontabs have changed).</p> 1183program when the crontabs have changed).</p>
1184 </dd>
1185 <dt>ev_tstamp offset [read-write]</dt>
1186 <dd>
1187 <p>When repeating, this contains the offset value, otherwise this is the
1188absolute point in time (the <code>at</code> value passed to <code>ev_periodic_set</code>).</p>
1189 <p>Can be modified any time, but changes only take effect when the periodic
1190timer fires or <code>ev_periodic_again</code> is being called.</p>
1180 </dd> 1191 </dd>
1181 <dt>ev_tstamp interval [read-write]</dt> 1192 <dt>ev_tstamp interval [read-write]</dt>
1182 <dd> 1193 <dd>
1183 <p>The current interval value. Can be modified any time, but changes only 1194 <p>The current interval value. Can be modified any time, but changes only
1184take effect when the periodic timer fires or <code>ev_periodic_again</code> is being 1195take effect when the periodic timer fires or <code>ev_periodic_again</code> is being
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1483are ready to run (it's actually more complicated: it only runs coroutines 1494are ready to run (it's actually more complicated: it only runs coroutines
1484with priority higher than or equal to the event loop and one coroutine 1495with priority higher than or equal to the event loop and one coroutine
1485of lower priority, but only once, using idle watchers to keep the event 1496of lower priority, but only once, using idle watchers to keep the event
1486loop from blocking if lower-priority coroutines are active, thus mapping 1497loop from blocking if lower-priority coroutines are active, thus mapping
1487low-priority coroutines to idle/background tasks).</p> 1498low-priority coroutines to idle/background tasks).</p>
1499<p>It is recommended to give <code>ev_check</code> watchers highest (<code>EV_MAXPRI</code>)
1500priority, to ensure that they are being run before any other watchers
1501after the poll. Also, <code>ev_check</code> watchers (and <code>ev_prepare</code> watchers,
1502too) should not activate (&quot;feed&quot;) events into libev. While libev fully
1503supports this, they will be called before other <code>ev_check</code> watchers did
1504their job. As <code>ev_check</code> watchers are often used to embed other event
1505loops those other event loops might be in an unusable state until their
1506<code>ev_check</code> watcher ran (always remind yourself to coexist peacefully with
1507others).</p>
1488<dl> 1508<dl>
1489 <dt>ev_prepare_init (ev_prepare *, callback)</dt> 1509 <dt>ev_prepare_init (ev_prepare *, callback)</dt>
1490 <dt>ev_check_init (ev_check *, callback)</dt> 1510 <dt>ev_check_init (ev_check *, callback)</dt>
1491 <dd> 1511 <dd>
1492 <p>Initialises and configures the prepare or check watcher - they have no 1512 <p>Initialises and configures the prepare or check watcher - they have no

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