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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="Tue Nov 27 21:29:04 2007" /> 9 <meta name="created" content="Thu Nov 29 18:28:02 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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133watcher.</p> 133watcher.</p>
134 134
135</div> 135</div>
136<h1 id="FEATURES">FEATURES</h1> 136<h1 id="FEATURES">FEATURES</h1>
137<div id="FEATURES_CONTENT"> 137<div id="FEATURES_CONTENT">
138<p>Libev supports <code>select</code>, <code>poll</code>, the linux-specific <code>epoll</code>, the 138<p>Libev supports <code>select</code>, <code>poll</code>, the Linux-specific <code>epoll</code>, the
139bsd-specific <code>kqueue</code> and the solaris-specific event port mechanisms 139BSD-specific <code>kqueue</code> and the Solaris-specific event port mechanisms
140for file descriptor events (<code>ev_io</code>), relative timers (<code>ev_timer</code>), 140for file descriptor events (<code>ev_io</code>), the Linux <code>inotify</code> interface
141(for <code>ev_stat</code>), relative timers (<code>ev_timer</code>), absolute timers
141absolute timers with customised rescheduling (<code>ev_periodic</code>), synchronous 142with customised rescheduling (<code>ev_periodic</code>), synchronous signals
142signals (<code>ev_signal</code>), process status change events (<code>ev_child</code>), and 143(<code>ev_signal</code>), process status change events (<code>ev_child</code>), and event
143event watchers dealing with the event loop mechanism itself (<code>ev_idle</code>, 144watchers dealing with the event loop mechanism itself (<code>ev_idle</code>,
144<code>ev_embed</code>, <code>ev_prepare</code> and <code>ev_check</code> watchers) as well as 145<code>ev_embed</code>, <code>ev_prepare</code> and <code>ev_check</code> watchers) as well as
145file watchers (<code>ev_stat</code>) and even limited support for fork events 146file watchers (<code>ev_stat</code>) and even limited support for fork events
146(<code>ev_fork</code>).</p> 147(<code>ev_fork</code>).</p>
147<p>It also is quite fast (see this 148<p>It also is quite fast (see this
148<a href="http://libev.schmorp.de/bench.html">benchmark</a> comparing it to libevent 149<a href="http://libev.schmorp.de/bench.html">benchmark</a> comparing it to libevent
… …
229might be supported on the current system, you would need to look at 230might be supported on the current system, you would need to look at
230<code>ev_embeddable_backends () &amp; ev_supported_backends ()</code>, likewise for 231<code>ev_embeddable_backends () &amp; ev_supported_backends ()</code>, likewise for
231recommended ones.</p> 232recommended ones.</p>
232 <p>See the description of <code>ev_embed</code> watchers for more info.</p> 233 <p>See the description of <code>ev_embed</code> watchers for more info.</p>
233 </dd> 234 </dd>
234 <dt>ev_set_allocator (void *(*cb)(void *ptr, size_t size))</dt> 235 <dt>ev_set_allocator (void *(*cb)(void *ptr, long size))</dt>
235 <dd> 236 <dd>
236 <p>Sets the allocation function to use (the prototype and semantics are 237 <p>Sets the allocation function to use (the prototype is similar - the
237identical to the realloc C function). It is used to allocate and free 238semantics is identical - to the realloc C function). It is used to
238memory (no surprises here). If it returns zero when memory needs to be 239allocate and free memory (no surprises here). If it returns zero when
239allocated, the library might abort or take some potentially destructive 240memory needs to be allocated, the library might abort or take some
240action. The default is your system realloc function.</p> 241potentially destructive action. The default is your system realloc
242function.</p>
241 <p>You could override this function in high-availability programs to, say, 243 <p>You could override this function in high-availability programs to, say,
242free some memory if it cannot allocate memory, to use a special allocator, 244free some memory if it cannot allocate memory, to use a special allocator,
243or even to sleep a while and retry until some memory is available.</p> 245or even to sleep a while and retry until some memory is available.</p>
244 <p>Example: Replace the libev allocator with one that waits a bit and then 246 <p>Example: Replace the libev allocator with one that waits a bit and then
245retries).</p> 247retries).</p>
… …
323or setgid) then libev will <i>not</i> look at the environment variable 325or setgid) then libev will <i>not</i> look at the environment variable
324<code>LIBEV_FLAGS</code>. Otherwise (the default), this environment variable will 326<code>LIBEV_FLAGS</code>. Otherwise (the default), this environment variable will
325override the flags completely if it is found in the environment. This is 327override the flags completely if it is found in the environment. This is
326useful to try out specific backends to test their performance, or to work 328useful to try out specific backends to test their performance, or to work
327around bugs.</p> 329around bugs.</p>
330 </dd>
331 <dt><code>EVFLAG_FORKCHECK</code></dt>
332 <dd>
333 <p>Instead of calling <code>ev_default_fork</code> or <code>ev_loop_fork</code> manually after
334a fork, you can also make libev check for a fork in each iteration by
335enabling this flag.</p>
336 <p>This works by calling <code>getpid ()</code> on every iteration of the loop,
337and thus this might slow down your event loop if you do a lot of loop
338iterations and little real work, but is usually not noticable (on my
339Linux system for example, <code>getpid</code> is actually a simple 5-insn sequence
340without a syscall and thus <i>very</i> fast, but my Linux system also has
341<code>pthread_atfork</code> which is even faster).</p>
342 <p>The big advantage of this flag is that you can forget about fork (and
343forget about forgetting to tell libev about forking) when you use this
344flag.</p>
345 <p>This flag setting cannot be overriden or specified in the <code>LIBEV_FLAGS</code>
346environment variable.</p>
328 </dd> 347 </dd>
329 <dt><code>EVBACKEND_SELECT</code> (value 1, portable select backend)</dt> 348 <dt><code>EVBACKEND_SELECT</code> (value 1, portable select backend)</dt>
330 <dd> 349 <dd>
331 <p>This is your standard select(2) backend. Not <i>completely</i> standard, as 350 <p>This is your standard select(2) backend. Not <i>completely</i> standard, as
332libev tries to roll its own fd_set with no limits on the number of fds, 351libev tries to roll its own fd_set with no limits on the number of fds,
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741events but its callback has not yet been invoked). As long as a watcher 760events but its callback has not yet been invoked). As long as a watcher
742is pending (but not active) you must not call an init function on it (but 761is pending (but not active) you must not call an init function on it (but
743<code>ev_TYPE_set</code> is safe) and you must make sure the watcher is available to 762<code>ev_TYPE_set</code> is safe) and you must make sure the watcher is available to
744libev (e.g. you cnanot <code>free ()</code> it).</p> 763libev (e.g. you cnanot <code>free ()</code> it).</p>
745 </dd> 764 </dd>
746 <dt>callback = ev_cb (ev_TYPE *watcher)</dt> 765 <dt>callback ev_cb (ev_TYPE *watcher)</dt>
747 <dd> 766 <dd>
748 <p>Returns the callback currently set on the watcher.</p> 767 <p>Returns the callback currently set on the watcher.</p>
749 </dd> 768 </dd>
750 <dt>ev_cb_set (ev_TYPE *watcher, callback)</dt> 769 <dt>ev_cb_set (ev_TYPE *watcher, callback)</dt>
751 <dd> 770 <dd>
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783 struct my_io *w = (struct my_io *)w_; 802 struct my_io *w = (struct my_io *)w_;
784 ... 803 ...
785 } 804 }
786 805
787</pre> 806</pre>
788<p>More interesting and less C-conformant ways of catsing your callback type 807<p>More interesting and less C-conformant ways of casting your callback type
789have been omitted....</p> 808instead have been omitted.</p>
809<p>Another common scenario is having some data structure with multiple
810watchers:</p>
811<pre> struct my_biggy
812 {
813 int some_data;
814 ev_timer t1;
815 ev_timer t2;
816 }
790 817
818</pre>
819<p>In this case getting the pointer to <code>my_biggy</code> is a bit more complicated,
820you need to use <code>offsetof</code>:</p>
821<pre> #include &lt;stddef.h&gt;
791 822
823 static void
824 t1_cb (EV_P_ struct ev_timer *w, int revents)
825 {
826 struct my_biggy big = (struct my_biggy *
827 (((char *)w) - offsetof (struct my_biggy, t1));
828 }
792 829
830 static void
831 t2_cb (EV_P_ struct ev_timer *w, int revents)
832 {
833 struct my_biggy big = (struct my_biggy *
834 (((char *)w) - offsetof (struct my_biggy, t2));
835 }
793 836
837
838
839
840</pre>
794 841
795</div> 842</div>
796<h1 id="WATCHER_TYPES">WATCHER TYPES</h1> 843<h1 id="WATCHER_TYPES">WATCHER TYPES</h1>
797<div id="WATCHER_TYPES_CONTENT"> 844<div id="WATCHER_TYPES_CONTENT">
798<p>This section describes each watcher in detail, but will not repeat 845<p>This section describes each watcher in detail, but will not repeat
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922 </dd> 969 </dd>
923 <dt>ev_timer_again (loop)</dt> 970 <dt>ev_timer_again (loop)</dt>
924 <dd> 971 <dd>
925 <p>This will act as if the timer timed out and restart it again if it is 972 <p>This will act as if the timer timed out and restart it again if it is
926repeating. The exact semantics are:</p> 973repeating. The exact semantics are:</p>
974 <p>If the timer is pending, its pending status is cleared.</p>
927 <p>If the timer is started but nonrepeating, stop it.</p> 975 <p>If the timer is started but nonrepeating, stop it (as if it timed out).</p>
928 <p>If the timer is repeating, either start it if necessary (with the repeat 976 <p>If the timer is repeating, either start it if necessary (with the
929value), or reset the running timer to the repeat value.</p> 977<code>repeat</code> value), or reset the running timer to the <code>repeat</code> value.</p>
930 <p>This sounds a bit complicated, but here is a useful and typical 978 <p>This sounds a bit complicated, but here is a useful and typical
931example: Imagine you have a tcp connection and you want a so-called 979example: Imagine you have a tcp connection and you want a so-called idle
932idle timeout, that is, you want to be called when there have been, 980timeout, that is, you want to be called when there have been, say, 60
933say, 60 seconds of inactivity on the socket. The easiest way to do 981seconds of inactivity on the socket. The easiest way to do this is to
934this is to configure an <code>ev_timer</code> with <code>after</code>=<code>repeat</code>=<code>60</code> and calling 982configure an <code>ev_timer</code> with a <code>repeat</code> value of <code>60</code> and then call
935<code>ev_timer_again</code> each time you successfully read or write some data. If 983<code>ev_timer_again</code> each time you successfully read or write some data. If
936you go into an idle state where you do not expect data to travel on the 984you go into an idle state where you do not expect data to travel on the
937socket, you can stop the timer, and again will automatically restart it if 985socket, you can <code>ev_timer_stop</code> the timer, and <code>ev_timer_again</code> will
938need be.</p> 986automatically restart it if need be.</p>
939 <p>You can also ignore the <code>after</code> value and <code>ev_timer_start</code> altogether 987 <p>That means you can ignore the <code>after</code> value and <code>ev_timer_start</code>
940and only ever use the <code>repeat</code> value:</p> 988altogether and only ever use the <code>repeat</code> value and <code>ev_timer_again</code>:</p>
941<pre> ev_timer_init (timer, callback, 0., 5.); 989<pre> ev_timer_init (timer, callback, 0., 5.);
942 ev_timer_again (loop, timer); 990 ev_timer_again (loop, timer);
943 ... 991 ...
944 timer-&gt;again = 17.; 992 timer-&gt;again = 17.;
945 ev_timer_again (loop, timer); 993 ev_timer_again (loop, timer);
946 ... 994 ...
947 timer-&gt;again = 10.; 995 timer-&gt;again = 10.;
948 ev_timer_again (loop, timer); 996 ev_timer_again (loop, timer);
949 997
950</pre> 998</pre>
951 <p>This is more efficient then stopping/starting the timer eahc time you want 999 <p>This is more slightly efficient then stopping/starting the timer each time
952to modify its timeout value.</p> 1000you want to modify its timeout value.</p>
953 </dd> 1001 </dd>
954 <dt>ev_tstamp repeat [read-write]</dt> 1002 <dt>ev_tstamp repeat [read-write]</dt>
955 <dd> 1003 <dd>
956 <p>The current <code>repeat</code> value. Will be used each time the watcher times out 1004 <p>The current <code>repeat</code> value. Will be used each time the watcher times out
957or <code>ev_timer_again</code> is called and determines the next timeout (if any), 1005or <code>ev_timer_again</code> is called and determines the next timeout (if any),
… …
1218<p>The path does not need to exist: changing from &quot;path exists&quot; to &quot;path does 1266<p>The path does not need to exist: changing from &quot;path exists&quot; to &quot;path does
1219not exist&quot; is a status change like any other. The condition &quot;path does 1267not exist&quot; is a status change like any other. The condition &quot;path does
1220not exist&quot; is signified by the <code>st_nlink</code> field being zero (which is 1268not exist&quot; is signified by the <code>st_nlink</code> field being zero (which is
1221otherwise always forced to be at least one) and all the other fields of 1269otherwise always forced to be at least one) and all the other fields of
1222the stat buffer having unspecified contents.</p> 1270the stat buffer having unspecified contents.</p>
1271<p>The path <i>should</i> be absolute and <i>must not</i> end in a slash. If it is
1272relative and your working directory changes, the behaviour is undefined.</p>
1223<p>Since there is no standard to do this, the portable implementation simply 1273<p>Since there is no standard to do this, the portable implementation simply
1224calls <code>stat (2)</code> regulalry on the path to see if it changed somehow. You 1274calls <code>stat (2)</code> regularly on the path to see if it changed somehow. You
1225can specify a recommended polling interval for this case. If you specify 1275can specify a recommended polling interval for this case. If you specify
1226a polling interval of <code>0</code> (highly recommended!) then a <i>suitable, 1276a polling interval of <code>0</code> (highly recommended!) then a <i>suitable,
1227unspecified default</i> value will be used (which you can expect to be around 1277unspecified default</i> value will be used (which you can expect to be around
1228five seconds, although this might change dynamically). Libev will also 1278five seconds, although this might change dynamically). Libev will also
1229impose a minimum interval which is currently around <code>0.1</code>, but thats 1279impose a minimum interval which is currently around <code>0.1</code>, but thats
1230usually overkill.</p> 1280usually overkill.</p>
1231<p>This watcher type is not meant for massive numbers of stat watchers, 1281<p>This watcher type is not meant for massive numbers of stat watchers,
1232as even with OS-supported change notifications, this can be 1282as even with OS-supported change notifications, this can be
1233resource-intensive.</p> 1283resource-intensive.</p>
1234<p>At the time of this writing, no specific OS backends are implemented, but 1284<p>At the time of this writing, only the Linux inotify interface is
1235if demand increases, at least a kqueue and inotify backend will be added.</p> 1285implemented (implementing kqueue support is left as an exercise for the
1286reader). Inotify will be used to give hints only and should not change the
1287semantics of <code>ev_stat</code> watchers, which means that libev sometimes needs
1288to fall back to regular polling again even with inotify, but changes are
1289usually detected immediately, and if the file exists there will be no
1290polling.</p>
1236<dl> 1291<dl>
1237 <dt>ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)</dt> 1292 <dt>ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)</dt>
1238 <dt>ev_stat_set (ev_stat *, const char *path, ev_tstamp interval)</dt> 1293 <dt>ev_stat_set (ev_stat *, const char *path, ev_tstamp interval)</dt>
1239 <dd> 1294 <dd>
1240 <p>Configures the watcher to wait for status changes of the given 1295 <p>Configures the watcher to wait for status changes of the given
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1987 </dd> 2042 </dd>
1988 <dt>EV_USE_DEVPOLL</dt> 2043 <dt>EV_USE_DEVPOLL</dt>
1989 <dd> 2044 <dd>
1990 <p>reserved for future expansion, works like the USE symbols above.</p> 2045 <p>reserved for future expansion, works like the USE symbols above.</p>
1991 </dd> 2046 </dd>
2047 <dt>EV_USE_INOTIFY</dt>
2048 <dd>
2049 <p>If defined to be <code>1</code>, libev will compile in support for the Linux inotify
2050interface to speed up <code>ev_stat</code> watchers. Its actual availability will
2051be detected at runtime.</p>
2052 </dd>
1992 <dt>EV_H</dt> 2053 <dt>EV_H</dt>
1993 <dd> 2054 <dd>
1994 <p>The name of the <cite>ev.h</cite> header file used to include it. The default if 2055 <p>The name of the <cite>ev.h</cite> header file used to include it. The default if
1995undefined is <code>&lt;ev.h&gt;</code> in <cite>event.h</cite> and <code>&quot;ev.h&quot;</code> in <cite>ev.c</cite>. This 2056undefined is <code>&lt;ev.h&gt;</code> in <cite>event.h</cite> and <code>&quot;ev.h&quot;</code> in <cite>ev.c</cite>. This
1996can be used to virtually rename the <cite>ev.h</cite> header file in case of conflicts.</p> 2057can be used to virtually rename the <cite>ev.h</cite> header file in case of conflicts.</p>
… …
2051 <dt>EV_PID_HASHSIZE</dt> 2112 <dt>EV_PID_HASHSIZE</dt>
2052 <dd> 2113 <dd>
2053 <p><code>ev_child</code> watchers use a small hash table to distribute workload by 2114 <p><code>ev_child</code> watchers use a small hash table to distribute workload by
2054pid. The default size is <code>16</code> (or <code>1</code> with <code>EV_MINIMAL</code>), usually more 2115pid. The default size is <code>16</code> (or <code>1</code> with <code>EV_MINIMAL</code>), usually more
2055than enough. If you need to manage thousands of children you might want to 2116than enough. If you need to manage thousands of children you might want to
2056increase this value.</p> 2117increase this value (<i>must</i> be a power of two).</p>
2118 </dd>
2119 <dt>EV_INOTIFY_HASHSIZE</dt>
2120 <dd>
2121 <p><code>ev_staz</code> watchers use a small hash table to distribute workload by
2122inotify watch id. The default size is <code>16</code> (or <code>1</code> with <code>EV_MINIMAL</code>),
2123usually more than enough. If you need to manage thousands of <code>ev_stat</code>
2124watchers you might want to increase this value (<i>must</i> be a power of
2125two).</p>
2057 </dd> 2126 </dd>
2058 <dt>EV_COMMON</dt> 2127 <dt>EV_COMMON</dt>
2059 <dd> 2128 <dd>
2060 <p>By default, all watchers have a <code>void *data</code> member. By redefining 2129 <p>By default, all watchers have a <code>void *data</code> member. By redefining
2061this macro to a something else you can include more and other types of 2130this macro to a something else you can include more and other types of
… …
2118 <dl> 2187 <dl>
2119 <dt>Starting and stopping timer/periodic watchers: O(log skipped_other_timers)</dt> 2188 <dt>Starting and stopping timer/periodic watchers: O(log skipped_other_timers)</dt>
2120 <dt>Changing timer/periodic watchers (by autorepeat, again): O(log skipped_other_timers)</dt> 2189 <dt>Changing timer/periodic watchers (by autorepeat, again): O(log skipped_other_timers)</dt>
2121 <dt>Starting io/check/prepare/idle/signal/child watchers: O(1)</dt> 2190 <dt>Starting io/check/prepare/idle/signal/child watchers: O(1)</dt>
2122 <dt>Stopping check/prepare/idle watchers: O(1)</dt> 2191 <dt>Stopping check/prepare/idle watchers: O(1)</dt>
2123 <dt>Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % 16))</dt> 2192 <dt>Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))</dt>
2124 <dt>Finding the next timer per loop iteration: O(1)</dt> 2193 <dt>Finding the next timer per loop iteration: O(1)</dt>
2125 <dt>Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)</dt> 2194 <dt>Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)</dt>
2126 <dt>Activating one watcher: O(1)</dt> 2195 <dt>Activating one watcher: O(1)</dt>
2127 </dl> 2196 </dl>
2128 </p> 2197 </p>

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