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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="Fri Nov 23 17:17:04 2007" /> 9 <meta name="created" content="Sat Nov 24 08:13:46 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 -->
… …
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="#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>
27</ul> 28</ul>
28</li> 29</li>
29<li><a href="#WATCHER_TYPES">WATCHER TYPES</a> 30<li><a href="#WATCHER_TYPES">WATCHER TYPES</a>
30<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>
31<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 recurring timeouts</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> 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_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>
34<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_wait_for_pid_stat"><code>ev_child</code> - wait for pid status changes</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_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> 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>
37</ul> 39</ul>
38</li> 40</li>
39<li><a href="#OTHER_FUNCTIONS">OTHER FUNCTIONS</a></li> 41<li><a href="#OTHER_FUNCTIONS">OTHER FUNCTIONS</a></li>
40<li><a href="#LIBEVENT_EMULATION">LIBEVENT EMULATION</a></li> 42<li><a href="#LIBEVENT_EMULATION">LIBEVENT EMULATION</a></li>
41<li><a href="#C_SUPPORT">C++ SUPPORT</a></li> 43<li><a href="#C_SUPPORT">C++ SUPPORT</a></li>
… …
156recommended for this platform. This set is often smaller than the one 158recommended for this platform. This set is often smaller than the one
157returned by <code>ev_supported_backends</code>, as for example kqueue is broken on 159returned by <code>ev_supported_backends</code>, as for example kqueue is broken on
158most BSDs and will not be autodetected unless you explicitly request it 160most BSDs and will not be autodetected unless you explicitly request it
159(assuming you know what you are doing). This is the set of backends that 161(assuming you know what you are doing). This is the set of backends that
160libev will probe for if you specify no backends explicitly.</p> 162libev will probe for if you specify no backends explicitly.</p>
163 </dd>
164 <dt>unsigned int ev_embeddable_backends ()</dt>
165 <dd>
166 <p>Returns the set of backends that are embeddable in other event loops. This
167is the theoretical, all-platform, value. To find which backends
168might be supported on the current system, you would need to look at
169<code>ev_embeddable_backends () &amp; ev_supported_backends ()</code>, likewise for
170recommended ones.</p>
171 <p>See the description of <code>ev_embed</code> watchers for more info.</p>
161 </dd> 172 </dd>
162 <dt>ev_set_allocator (void *(*cb)(void *ptr, long size))</dt> 173 <dt>ev_set_allocator (void *(*cb)(void *ptr, long size))</dt>
163 <dd> 174 <dd>
164 <p>Sets the allocation function to use (the prototype is similar to the 175 <p>Sets the allocation function to use (the prototype is similar to the
165realloc C function, the semantics are identical). It is used to allocate 176realloc C function, the semantics are identical). It is used to allocate
… …
525with a watcher-specific start function (<code>ev_&lt;type&gt;_start (loop, watcher 536with a watcher-specific start function (<code>ev_&lt;type&gt;_start (loop, watcher
526*)</code>), and you can stop watching for events at any time by calling the 537*)</code>), and you can stop watching for events at any time by calling the
527corresponding stop function (<code>ev_&lt;type&gt;_stop (loop, watcher *)</code>.</p> 538corresponding stop function (<code>ev_&lt;type&gt;_stop (loop, watcher *)</code>.</p>
528<p>As long as your watcher is active (has been started but not stopped) you 539<p>As long as your watcher is active (has been started but not stopped) you
529must not touch the values stored in it. Most specifically you must never 540must not touch the values stored in it. Most specifically you must never
530reinitialise it or call its set macro.</p> 541reinitialise it or call its <code>set</code> macro.</p>
531<p>You can check whether an event is active by calling the <code>ev_is_active
532(watcher *)</code> macro. To see whether an event is outstanding (but the
533callback for it has not been called yet) you can use the <code>ev_is_pending
534(watcher *)</code> macro.</p>
535<p>Each and every callback receives the event loop pointer as first, the 542<p>Each and every callback receives the event loop pointer as first, the
536registered watcher structure as second, and a bitset of received events as 543registered watcher structure as second, and a bitset of received events as
537third argument.</p> 544third argument.</p>
538<p>The received events usually include a single bit per event type received 545<p>The received events usually include a single bit per event type received
539(you can receive multiple events at the same time). The possible bit masks 546(you can receive multiple events at the same time). The possible bit masks
… …
588your callbacks is well-written it can just attempt the operation and cope 595your callbacks is well-written it can just attempt the operation and cope
589with the error from read() or write(). This will not work in multithreaded 596with the error from read() or write(). This will not work in multithreaded
590programs, though, so beware.</p> 597programs, though, so beware.</p>
591 </dd> 598 </dd>
592</dl> 599</dl>
600
601</div>
602<h2 id="SUMMARY_OF_GENERIC_WATCHER_FUNCTIONS">SUMMARY OF GENERIC WATCHER FUNCTIONS</h2>
603<div id="SUMMARY_OF_GENERIC_WATCHER_FUNCTIONS-2">
604<p>In the following description, <code>TYPE</code> stands for the watcher type,
605e.g. <code>timer</code> for <code>ev_timer</code> watchers and <code>io</code> for <code>ev_io</code> watchers.</p>
606<dl>
607 <dt><code>ev_init</code> (ev_TYPE *watcher, callback)</dt>
608 <dd>
609 <p>This macro initialises the generic portion of a watcher. The contents
610of the watcher object can be arbitrary (so <code>malloc</code> will do). Only
611the generic parts of the watcher are initialised, you <i>need</i> to call
612the type-specific <code>ev_TYPE_set</code> macro afterwards to initialise the
613type-specific parts. For each type there is also a <code>ev_TYPE_init</code> macro
614which rolls both calls into one.</p>
615 <p>You can reinitialise a watcher at any time as long as it has been stopped
616(or never started) and there are no pending events outstanding.</p>
617 <p>The callbakc is always of type <code>void (*)(ev_loop *loop, ev_TYPE *watcher,
618int revents)</code>.</p>
619 </dd>
620 <dt><code>ev_TYPE_set</code> (ev_TYPE *, [args])</dt>
621 <dd>
622 <p>This macro initialises the type-specific parts of a watcher. You need to
623call <code>ev_init</code> at least once before you call this macro, but you can
624call <code>ev_TYPE_set</code> any number of times. You must not, however, call this
625macro on a watcher that is active (it can be pending, however, which is a
626difference to the <code>ev_init</code> macro).</p>
627 <p>Although some watcher types do not have type-specific arguments
628(e.g. <code>ev_prepare</code>) you still need to call its <code>set</code> macro.</p>
629 </dd>
630 <dt><code>ev_TYPE_init</code> (ev_TYPE *watcher, callback, [args])</dt>
631 <dd>
632 <p>This convinience macro rolls both <code>ev_init</code> and <code>ev_TYPE_set</code> macro
633calls into a single call. This is the most convinient method to initialise
634a watcher. The same limitations apply, of course.</p>
635 </dd>
636 <dt><code>ev_TYPE_start</code> (loop *, ev_TYPE *watcher)</dt>
637 <dd>
638 <p>Starts (activates) the given watcher. Only active watchers will receive
639events. If the watcher is already active nothing will happen.</p>
640 </dd>
641 <dt><code>ev_TYPE_stop</code> (loop *, ev_TYPE *watcher)</dt>
642 <dd>
643 <p>Stops the given watcher again (if active) and clears the pending
644status. It is possible that stopped watchers are pending (for example,
645non-repeating timers are being stopped when they become pending), but
646<code>ev_TYPE_stop</code> ensures that the watcher is neither active nor pending. If
647you want to free or reuse the memory used by the watcher it is therefore a
648good idea to always call its <code>ev_TYPE_stop</code> function.</p>
649 </dd>
650 <dt>bool ev_is_active (ev_TYPE *watcher)</dt>
651 <dd>
652 <p>Returns a true value iff the watcher is active (i.e. it has been started
653and not yet been stopped). As long as a watcher is active you must not modify
654it.</p>
655 </dd>
656 <dt>bool ev_is_pending (ev_TYPE *watcher)</dt>
657 <dd>
658 <p>Returns a true value iff the watcher is pending, (i.e. it has outstanding
659events but its callback has not yet been invoked). As long as a watcher
660is pending (but not active) you must not call an init function on it (but
661<code>ev_TYPE_set</code> is safe) and you must make sure the watcher is available to
662libev (e.g. you cnanot <code>free ()</code> it).</p>
663 </dd>
664 <dt>callback = ev_cb (ev_TYPE *watcher)</dt>
665 <dd>
666 <p>Returns the callback currently set on the watcher.</p>
667 </dd>
668 <dt>ev_cb_set (ev_TYPE *watcher, callback)</dt>
669 <dd>
670 <p>Change the callback. You can change the callback at virtually any time
671(modulo threads).</p>
672 </dd>
673</dl>
674
675
676
677
593 678
594</div> 679</div>
595<h2 id="ASSOCIATING_CUSTOM_DATA_WITH_A_WATCH">ASSOCIATING CUSTOM DATA WITH A WATCHER</h2> 680<h2 id="ASSOCIATING_CUSTOM_DATA_WITH_A_WATCH">ASSOCIATING CUSTOM DATA WITH A WATCHER</h2>
596<div id="ASSOCIATING_CUSTOM_DATA_WITH_A_WATCH-2"> 681<div id="ASSOCIATING_CUSTOM_DATA_WITH_A_WATCH-2">
597<p>Each watcher has, by default, a member <code>void *data</code> that you can change 682<p>Each watcher has, by default, a member <code>void *data</code> that you can change
… …
931 <p>Configures the watcher to trigger on the given signal number (usually one 1016 <p>Configures the watcher to trigger on the given signal number (usually one
932of the <code>SIGxxx</code> constants).</p> 1017of the <code>SIGxxx</code> constants).</p>
933 </dd> 1018 </dd>
934</dl> 1019</dl>
935 1020
1021
1022
1023
1024
936</div> 1025</div>
937<h2 id="code_ev_child_code_wait_for_pid_stat"><code>ev_child</code> - wait for pid status changes</h2> 1026<h2 id="code_ev_child_code_wait_for_pid_stat"><code>ev_child</code> - wait for pid status changes</h2>
938<div id="code_ev_child_code_wait_for_pid_stat-2"> 1027<div id="code_ev_child_code_wait_for_pid_stat-2">
939<p>Child watchers trigger when your process receives a SIGCHLD in response to 1028<p>Child watchers trigger when your process receives a SIGCHLD in response to
940some child status changes (most typically when a child of yours dies).</p> 1029some child status changes (most typically when a child of yours dies).</p>
… …
1013<h2 id="code_ev_prepare_code_and_code_ev_che"><code>ev_prepare</code> and <code>ev_check</code> - customise your event loop</h2> 1102<h2 id="code_ev_prepare_code_and_code_ev_che"><code>ev_prepare</code> and <code>ev_check</code> - customise your event loop</h2>
1014<div id="code_ev_prepare_code_and_code_ev_che-2"> 1103<div id="code_ev_prepare_code_and_code_ev_che-2">
1015<p>Prepare and check watchers are usually (but not always) used in tandem: 1104<p>Prepare and check watchers are usually (but not always) used in tandem:
1016prepare watchers get invoked before the process blocks and check watchers 1105prepare watchers get invoked before the process blocks and check watchers
1017afterwards.</p> 1106afterwards.</p>
1018<p>Their main purpose is to integrate other event mechanisms into libev. This 1107<p>Their main purpose is to integrate other event mechanisms into libev and
1019could be used, for example, to track variable changes, implement your own 1108their use is somewhat advanced. This could be used, for example, to track
1020watchers, integrate net-snmp or a coroutine library and lots more.</p> 1109variable changes, implement your own watchers, integrate net-snmp or a
1110coroutine library and lots more.</p>
1021<p>This is done by examining in each prepare call which file descriptors need 1111<p>This is done by examining in each prepare call which file descriptors need
1022to be watched by the other library, registering <code>ev_io</code> watchers for 1112to be watched by the other library, registering <code>ev_io</code> watchers for
1023them and starting an <code>ev_timer</code> watcher for any timeouts (many libraries 1113them and starting an <code>ev_timer</code> watcher for any timeouts (many libraries
1024provide just this functionality). Then, in the check watcher you check for 1114provide just this functionality). Then, in the check watcher you check for
1025any events that occured (by checking the pending status of all watchers 1115any events that occured (by checking the pending status of all watchers
… …
1042parameters of any kind. There are <code>ev_prepare_set</code> and <code>ev_check_set</code> 1132parameters of any kind. There are <code>ev_prepare_set</code> and <code>ev_check_set</code>
1043macros, but using them is utterly, utterly and completely pointless.</p> 1133macros, but using them is utterly, utterly and completely pointless.</p>
1044 </dd> 1134 </dd>
1045</dl> 1135</dl>
1046<p>Example: *TODO*.</p> 1136<p>Example: *TODO*.</p>
1137
1138
1139
1140
1141
1142</div>
1143<h2 id="code_ev_embed_code_when_one_backend_"><code>ev_embed</code> - when one backend isn't enough</h2>
1144<div id="code_ev_embed_code_when_one_backend_-2">
1145<p>This is a rather advanced watcher type that lets you embed one event loop
1146into another (currently only <code>ev_io</code> events are supported in the embedded
1147loop, other types of watchers might be handled in a delayed or incorrect
1148fashion and must not be used).</p>
1149<p>There are primarily two reasons you would want that: work around bugs and
1150prioritise I/O.</p>
1151<p>As an example for a bug workaround, the kqueue backend might only support
1152sockets on some platform, so it is unusable as generic backend, but you
1153still want to make use of it because you have many sockets and it scales
1154so nicely. In this case, you would create a kqueue-based loop and embed it
1155into your default loop (which might use e.g. poll). Overall operation will
1156be a bit slower because first libev has to poll and then call kevent, but
1157at least you can use both at what they are best.</p>
1158<p>As for prioritising I/O: rarely you have the case where some fds have
1159to be watched and handled very quickly (with low latency), and even
1160priorities and idle watchers might have too much overhead. In this case
1161you would put all the high priority stuff in one loop and all the rest in
1162a second one, and embed the second one in the first.</p>
1163<p>As long as the watcher is active, the callback will be invoked every time
1164there might be events pending in the embedded loop. The callback must then
1165call <code>ev_embed_sweep (mainloop, watcher)</code> to make a single sweep and invoke
1166their callbacks (you could also start an idle watcher to give the embedded
1167loop strictly lower priority for example). You can also set the callback
1168to <code>0</code>, in which case the embed watcher will automatically execute the
1169embedded loop sweep.</p>
1170<p>As long as the watcher is started it will automatically handle events. The
1171callback will be invoked whenever some events have been handled. You can
1172set the callback to <code>0</code> to avoid having to specify one if you are not
1173interested in that.</p>
1174<p>Also, there have not currently been made special provisions for forking:
1175when you fork, you not only have to call <code>ev_loop_fork</code> on both loops,
1176but you will also have to stop and restart any <code>ev_embed</code> watchers
1177yourself.</p>
1178<p>Unfortunately, not all backends are embeddable, only the ones returned by
1179<code>ev_embeddable_backends</code> are, which, unfortunately, does not include any
1180portable one.</p>
1181<p>So when you want to use this feature you will always have to be prepared
1182that you cannot get an embeddable loop. The recommended way to get around
1183this is to have a separate variables for your embeddable loop, try to
1184create it, and if that fails, use the normal loop for everything:</p>
1185<pre> struct ev_loop *loop_hi = ev_default_init (0);
1186 struct ev_loop *loop_lo = 0;
1187 struct ev_embed embed;
1188
1189 // see if there is a chance of getting one that works
1190 // (remember that a flags value of 0 means autodetection)
1191 loop_lo = ev_embeddable_backends () &amp; ev_recommended_backends ()
1192 ? ev_loop_new (ev_embeddable_backends () &amp; ev_recommended_backends ())
1193 : 0;
1194
1195 // if we got one, then embed it, otherwise default to loop_hi
1196 if (loop_lo)
1197 {
1198 ev_embed_init (&amp;embed, 0, loop_lo);
1199 ev_embed_start (loop_hi, &amp;embed);
1200 }
1201 else
1202 loop_lo = loop_hi;
1203
1204</pre>
1205<dl>
1206 <dt>ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)</dt>
1207 <dt>ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)</dt>
1208 <dd>
1209 <p>Configures the watcher to embed the given loop, which must be
1210embeddable. If the callback is <code>0</code>, then <code>ev_embed_sweep</code> will be
1211invoked automatically, otherwise it is the responsibility of the callback
1212to invoke it (it will continue to be called until the sweep has been done,
1213if you do not want thta, you need to temporarily stop the embed watcher).</p>
1214 </dd>
1215 <dt>ev_embed_sweep (loop, ev_embed *)</dt>
1216 <dd>
1217 <p>Make a single, non-blocking sweep over the embedded loop. This works
1218similarly to <code>ev_loop (embedded_loop, EVLOOP_NONBLOCK)</code>, but in the most
1219apropriate way for embedded loops.</p>
1220 </dd>
1221</dl>
1047 1222
1048 1223
1049 1224
1050 1225
1051 1226
… …
1082 1257
1083 ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0); 1258 ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
1084 1259
1085</pre> 1260</pre>
1086 </dd> 1261 </dd>
1087 <dt>ev_feed_event (loop, watcher, int events)</dt> 1262 <dt>ev_feed_event (ev_loop *, watcher *, int revents)</dt>
1088 <dd> 1263 <dd>
1089 <p>Feeds the given event set into the event loop, as if the specified event 1264 <p>Feeds the given event set into the event loop, as if the specified event
1090had happened for the specified watcher (which must be a pointer to an 1265had happened for the specified watcher (which must be a pointer to an
1091initialised but not necessarily started event watcher).</p> 1266initialised but not necessarily started event watcher).</p>
1092 </dd> 1267 </dd>
1093 <dt>ev_feed_fd_event (loop, int fd, int revents)</dt> 1268 <dt>ev_feed_fd_event (ev_loop *, int fd, int revents)</dt>
1094 <dd> 1269 <dd>
1095 <p>Feed an event on the given fd, as if a file descriptor backend detected 1270 <p>Feed an event on the given fd, as if a file descriptor backend detected
1096the given events it.</p> 1271the given events it.</p>
1097 </dd> 1272 </dd>
1098 <dt>ev_feed_signal_event (loop, int signum)</dt> 1273 <dt>ev_feed_signal_event (ev_loop *loop, int signum)</dt>
1099 <dd> 1274 <dd>
1100 <p>Feed an event as if the given signal occured (loop must be the default loop!).</p> 1275 <p>Feed an event as if the given signal occured (<code>loop</code> must be the default
1276loop!).</p>
1101 </dd> 1277 </dd>
1102</dl> 1278</dl>
1103 1279
1104 1280
1105 1281

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