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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 08:58:02 2007" /> 9 <meta name="created" content="Mon Nov 12 09:58:24 2007" />
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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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17<ul><li><a href="#NAME">NAME</a></li> 17<ul><li><a href="#NAME">NAME</a></li>
18<li><a href="#SYNOPSIS">SYNOPSIS</a></li> 18<li><a href="#SYNOPSIS">SYNOPSIS</a></li>
19<li><a href="#DESCRIPTION">DESCRIPTION</a></li> 19<li><a href="#DESCRIPTION">DESCRIPTION</a></li>
20<li><a href="#FEATURES">FEATURES</a></li> 20<li><a href="#FEATURES">FEATURES</a></li>
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_AND_OTHER_GLOBAL_FUNCTIONS">TIME AND OTHER GLOBAL FUNCTIONS</a></li> 23<li><a href="#GLOBAL_FUNCTIONS">GLOBAL FUNCTIONS</a></li>
23<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>
24<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>
25<ul><li><a href="#ASSOCIATING_CUSTOM_DATA_WITH_A_WATCH">ASSOCIATING CUSTOM DATA WITH A WATCHER</a></li> 26<ul><li><a href="#ASSOCIATING_CUSTOM_DATA_WITH_A_WATCH">ASSOCIATING CUSTOM DATA WITH A WATCHER</a></li>
26</ul> 27</ul>
27</li> 28</li>
28<li><a href="#WATCHER_TYPES">WATCHER TYPES</a> 29<li><a href="#WATCHER_TYPES">WATCHER TYPES</a>
29<ul><li><a href="#struct_ev_io_is_my_file_descriptor_r">struct ev_io - is my file descriptor readable or writable</a></li> 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>
30<li><a href="#struct_ev_timer_relative_and_optiona">struct ev_timer - relative and optionally recurring timeouts</a></li> 31<li><a href="#code_ev_timer_code_relative_and_opti"><code>ev_timer</code> - relative and optionally recurring timeouts</a></li>
31<li><a href="#ev_periodic">ev_periodic</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>
32<li><a href="#ev_signal_signal_me_when_a_signal_ge">ev_signal - signal me when a signal gets signalled</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>
33<li><a href="#ev_child_wait_for_pid_status_changes">ev_child - wait for pid status changes</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>
34<li><a href="#ev_idle_when_you_ve_got_nothing_bett">ev_idle - 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>
35<li><a href="#prepare_and_check_your_hooks_into_th">prepare and check - your hooks into the 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>
36</ul> 37</ul>
37</li> 38</li>
38<li><a href="#OTHER_FUNCTIONS">OTHER FUNCTIONS</a></li> 39<li><a href="#OTHER_FUNCTIONS">OTHER FUNCTIONS</a></li>
39<li><a href="#AUTHOR">AUTHOR</a> 40<li><a href="#AUTHOR">AUTHOR</a>
40</li> 41</li>
… …
55</div> 56</div>
56<h1 id="DESCRIPTION">DESCRIPTION</h1><p><a href="#TOP" class="toplink">Top</a></p> 57<h1 id="DESCRIPTION">DESCRIPTION</h1><p><a href="#TOP" class="toplink">Top</a></p>
57<div id="DESCRIPTION_CONTENT"> 58<div id="DESCRIPTION_CONTENT">
58<p>Libev is an event loop: you register interest in certain events (such as a 59<p>Libev is an event loop: you register interest in certain events (such as a
59file descriptor being readable or a timeout occuring), and it will manage 60file descriptor being readable or a timeout occuring), and it will manage
60these event sources and provide your program events.</p> 61these event sources and provide your program with events.</p>
61<p>To do this, it must take more or less complete control over your process 62<p>To do this, it must take more or less complete control over your process
62(or thread) by executing the <i>event loop</i> handler, and will then 63(or thread) by executing the <i>event loop</i> handler, and will then
63communicate events via a callback mechanism.</p> 64communicate events via a callback mechanism.</p>
64<p>You register interest in certain events by registering so-called <i>event 65<p>You register interest in certain events by registering so-called <i>event
65watchers</i>, which are relatively small C structures you initialise with the 66watchers</i>, which are relatively small C structures you initialise with the
… …
71<div id="FEATURES_CONTENT"> 72<div id="FEATURES_CONTENT">
72<p>Libev supports select, poll, the linux-specific epoll and the bsd-specific 73<p>Libev supports select, poll, the linux-specific epoll and the bsd-specific
73kqueue mechanisms for file descriptor events, relative timers, absolute 74kqueue mechanisms for file descriptor events, relative timers, absolute
74timers with customised rescheduling, signal events, process status change 75timers with customised rescheduling, signal events, process status change
75events (related to SIGCHLD), and event watchers dealing with the event 76events (related to SIGCHLD), and event watchers dealing with the event
76loop mechanism itself (idle, prepare and check watchers).</p> 77loop mechanism itself (idle, prepare and check watchers). It also is quite
78fast (see this <a href="http://libev.schmorp.de/bench.html">benchmark</a> comparing
79it to libevent for example).</p>
77 80
78</div> 81</div>
79<h1 id="CONVENTIONS">CONVENTIONS</h1><p><a href="#TOP" class="toplink">Top</a></p> 82<h1 id="CONVENTIONS">CONVENTIONS</h1><p><a href="#TOP" class="toplink">Top</a></p>
80<div id="CONVENTIONS_CONTENT"> 83<div id="CONVENTIONS_CONTENT">
81<p>Libev is very configurable. In this manual the default configuration 84<p>Libev is very configurable. In this manual the default configuration
82will be described, which supports multiple event loops. For more info 85will be described, which supports multiple event loops. For more info
83about various configuraiton options please have a look at the file 86about various configuration options please have a look at the file
84<cite>README.embed</cite> in the libev distribution. If libev was configured without 87<cite>README.embed</cite> in the libev distribution. If libev was configured without
85support for multiple event loops, then all functions taking an initial 88support for multiple event loops, then all functions taking an initial
86argument of name <code>loop</code> (which is always of type <code>struct ev_loop *</code>) 89argument of name <code>loop</code> (which is always of type <code>struct ev_loop *</code>)
87will not have this argument.</p> 90will not have this argument.</p>
88 91
89</div> 92</div>
90<h1 id="TIME_AND_OTHER_GLOBAL_FUNCTIONS">TIME AND OTHER GLOBAL FUNCTIONS</h1><p><a href="#TOP" class="toplink">Top</a></p> 93<h1 id="TIME_REPRESENTATION">TIME REPRESENTATION</h1><p><a href="#TOP" class="toplink">Top</a></p>
91<div id="TIME_AND_OTHER_GLOBAL_FUNCTIONS_CONT"> 94<div id="TIME_REPRESENTATION_CONTENT">
92<p>Libev represents time as a single floating point number. This type is 95<p>Libev represents time as a single floating point number, representing the
96(fractional) number of seconds since the (POSIX) epoch (somewhere near
97the beginning of 1970, details are complicated, don't ask). This type is
93called <code>ev_tstamp</code>, which is what you should use too. It usually aliases 98called <code>ev_tstamp</code>, which is what you should use too. It usually aliases
94to the double type in C.</p> 99to the double type in C.</p>
100
101</div>
102<h1 id="GLOBAL_FUNCTIONS">GLOBAL FUNCTIONS</h1><p><a href="#TOP" class="toplink">Top</a></p>
103<div id="GLOBAL_FUNCTIONS_CONTENT">
95<dl> 104<dl>
96 <dt>ev_tstamp ev_time ()</dt> 105 <dt>ev_tstamp ev_time ()</dt>
97 <dd> 106 <dd>
98 <p>Returns the current time as libev would use it.</p> 107 <p>Returns the current time as libev would use it.</p>
99 </dd> 108 </dd>
… …
103 <p>You can find out the major and minor version numbers of the library 112 <p>You can find out the major and minor version numbers of the library
104you linked against by calling the functions <code>ev_version_major</code> and 113you linked against by calling the functions <code>ev_version_major</code> and
105<code>ev_version_minor</code>. If you want, you can compare against the global 114<code>ev_version_minor</code>. If you want, you can compare against the global
106symbols <code>EV_VERSION_MAJOR</code> and <code>EV_VERSION_MINOR</code>, which specify the 115symbols <code>EV_VERSION_MAJOR</code> and <code>EV_VERSION_MINOR</code>, which specify the
107version of the library your program was compiled against.</p> 116version of the library your program was compiled against.</p>
108 <p>Usually, its a good idea to terminate if the major versions mismatch, 117 <p>Usually, it's a good idea to terminate if the major versions mismatch,
109as this indicates an incompatible change. Minor versions are usually 118as this indicates an incompatible change. Minor versions are usually
110compatible to older versions, so a larger minor version alone is usually 119compatible to older versions, so a larger minor version alone is usually
111not a problem.</p> 120not a problem.</p>
112 </dd> 121 </dd>
113 <dt>ev_set_allocator (void *(*cb)(void *ptr, long size))</dt> 122 <dt>ev_set_allocator (void *(*cb)(void *ptr, long size))</dt>
114 <dd> 123 <dd>
115 <p>Sets the allocation function to use (the prototype is similar to the 124 <p>Sets the allocation function to use (the prototype is similar to the
116realloc function). It is used to allocate and free memory (no surprises 125realloc C function, the semantics are identical). It is used to allocate
117here). If it returns zero when memory needs to be allocated, the library 126and free memory (no surprises here). If it returns zero when memory
118might abort or take some potentially destructive action. The default is 127needs to be allocated, the library might abort or take some potentially
119your system realloc function.</p> 128destructive action. The default is your system realloc function.</p>
120 <p>You could override this function in high-availability programs to, say, 129 <p>You could override this function in high-availability programs to, say,
121free some memory if it cannot allocate memory, to use a special allocator, 130free some memory if it cannot allocate memory, to use a special allocator,
122or even to sleep a while and retry until some memory is available.</p> 131or even to sleep a while and retry until some memory is available.</p>
123 </dd> 132 </dd>
124 <dt>ev_set_syserr_cb (void (*cb)(const char *msg));</dt> 133 <dt>ev_set_syserr_cb (void (*cb)(const char *msg));</dt>
125 <dd> 134 <dd>
126 <p>Set the callback function to call on a retryable syscall error (such 135 <p>Set the callback function to call on a retryable syscall error (such
127as failed select, poll, epoll_wait). The message is a printable string 136as failed select, poll, epoll_wait). The message is a printable string
128indicating the system call or subsystem causing the problem. If this 137indicating the system call or subsystem causing the problem. If this
129callback is set, then libev will expect it to remedy the sitution, no 138callback is set, then libev will expect it to remedy the sitution, no
130matter what, when it returns. That is, libev will geenrally retry the 139matter what, when it returns. That is, libev will generally retry the
131requested operation, or, if the condition doesn't go away, do bad stuff 140requested operation, or, if the condition doesn't go away, do bad stuff
132(such as abort).</p> 141(such as abort).</p>
133 </dd> 142 </dd>
134</dl> 143</dl>
135 144
… …
138<div id="FUNCTIONS_CONTROLLING_THE_EVENT_LOOP-2"> 147<div id="FUNCTIONS_CONTROLLING_THE_EVENT_LOOP-2">
139<p>An event loop is described by a <code>struct ev_loop *</code>. The library knows two 148<p>An event loop is described by a <code>struct ev_loop *</code>. The library knows two
140types of such loops, the <i>default</i> loop, which supports signals and child 149types of such loops, the <i>default</i> loop, which supports signals and child
141events, and dynamically created loops which do not.</p> 150events, and dynamically created loops which do not.</p>
142<p>If you use threads, a common model is to run the default event loop 151<p>If you use threads, a common model is to run the default event loop
143in your main thread (or in a separate thrad) and for each thread you 152in your main thread (or in a separate thread) and for each thread you
144create, you also create another event loop. Libev itself does no lockign 153create, you also create another event loop. Libev itself does no locking
145whatsoever, so if you mix calls to different event loops, make sure you 154whatsoever, so if you mix calls to the same event loop in different
146lock (this is usually a bad idea, though, even if done right).</p> 155threads, make sure you lock (this is usually a bad idea, though, even if
156done correctly, because it's hideous and inefficient).</p>
147<dl> 157<dl>
148 <dt>struct ev_loop *ev_default_loop (unsigned int flags)</dt> 158 <dt>struct ev_loop *ev_default_loop (unsigned int flags)</dt>
149 <dd> 159 <dd>
150 <p>This will initialise the default event loop if it hasn't been initialised 160 <p>This will initialise the default event loop if it hasn't been initialised
151yet and return it. If the default loop could not be initialised, returns 161yet and return it. If the default loop could not be initialised, returns
152false. If it already was initialised it simply returns it (and ignores the 162false. If it already was initialised it simply returns it (and ignores the
153flags).</p> 163flags).</p>
154 <p>If you don't know what event loop to use, use the one returned from this 164 <p>If you don't know what event loop to use, use the one returned from this
155function.</p> 165function.</p>
156 <p>The flags argument can be used to specify special behaviour or specific 166 <p>The flags argument can be used to specify special behaviour or specific
157backends to use, and is usually specified as 0 (or EVFLAG_AUTO)</p> 167backends to use, and is usually specified as 0 (or EVFLAG_AUTO).</p>
158 <p>It supports the following flags:</p> 168 <p>It supports the following flags:</p>
159 <p> 169 <p>
160 <dl> 170 <dl>
161 <dt>EVFLAG_AUTO</dt> 171 <dt><code>EVFLAG_AUTO</code></dt>
162 <dd> 172 <dd>
163 <p>The default flags value. Use this if you have no clue (its the right 173 <p>The default flags value. Use this if you have no clue (it's the right
164thing, believe me).</p> 174thing, believe me).</p>
165 </dd> 175 </dd>
166 <dt>EVFLAG_NOENV</dt> 176 <dt><code>EVFLAG_NOENV</code></dt>
167 <dd> 177 <dd>
168 <p>If this flag bit is ored into the flag value then libev will <i>not</i> look 178 <p>If this flag bit is ored into the flag value (or the program runs setuid
169at the environment variable <code>LIBEV_FLAGS</code>. Otherwise (the default), this 179or setgid) then libev will <i>not</i> look at the environment variable
170environment variable will override the flags completely. This is useful 180<code>LIBEV_FLAGS</code>. Otherwise (the default), this environment variable will
181override the flags completely if it is found in the environment. This is
171to try out specific backends to tets their performance, or to work around 182useful to try out specific backends to test their performance, or to work
172bugs.</p> 183around bugs.</p>
173 </dd> 184 </dd>
174 <dt>EVMETHOD_SELECT portable select backend</dt> 185 <dt><code>EVMETHOD_SELECT</code> (portable select backend)</dt>
175 <dt>EVMETHOD_POLL poll backend (everywhere except windows)</dt> 186 <dt><code>EVMETHOD_POLL</code> (poll backend, available everywhere except on windows)</dt>
176 <dt>EVMETHOD_EPOLL linux only</dt> 187 <dt><code>EVMETHOD_EPOLL</code> (linux only)</dt>
177 <dt>EVMETHOD_KQUEUE some bsds only</dt> 188 <dt><code>EVMETHOD_KQUEUE</code> (some bsds only)</dt>
178 <dt>EVMETHOD_DEVPOLL solaris 8 only</dt> 189 <dt><code>EVMETHOD_DEVPOLL</code> (solaris 8 only)</dt>
179 <dt>EVMETHOD_PORT solaris 10 only</dt> 190 <dt><code>EVMETHOD_PORT</code> (solaris 10 only)</dt>
180 <dd> 191 <dd>
181 <p>If one or more of these are ored into the flags value, then only these 192 <p>If one or more of these are ored into the flags value, then only these
182backends will be tried (in the reverse order as given here). If one are 193backends will be tried (in the reverse order as given here). If one are
183specified, any backend will do.</p> 194specified, any backend will do.</p>
184 </dd> 195 </dd>
… …
194 </dd> 205 </dd>
195 <dt>ev_default_destroy ()</dt> 206 <dt>ev_default_destroy ()</dt>
196 <dd> 207 <dd>
197 <p>Destroys the default loop again (frees all memory and kernel state 208 <p>Destroys the default loop again (frees all memory and kernel state
198etc.). This stops all registered event watchers (by not touching them in 209etc.). This stops all registered event watchers (by not touching them in
199any way whatsoever, although you cnanot rely on this :).</p> 210any way whatsoever, although you cannot rely on this :).</p>
200 </dd> 211 </dd>
201 <dt>ev_loop_destroy (loop)</dt> 212 <dt>ev_loop_destroy (loop)</dt>
202 <dd> 213 <dd>
203 <p>Like <code>ev_default_destroy</code>, but destroys an event loop created by an 214 <p>Like <code>ev_default_destroy</code>, but destroys an event loop created by an
204earlier call to <code>ev_loop_new</code>.</p> 215earlier call to <code>ev_loop_new</code>.</p>
… …
210after forking, in either the parent or child process (or both, but that 221after forking, in either the parent or child process (or both, but that
211again makes little sense).</p> 222again makes little sense).</p>
212 <p>You <i>must</i> call this function after forking if and only if you want to 223 <p>You <i>must</i> call this function after forking if and only if you want to
213use the event library in both processes. If you just fork+exec, you don't 224use the event library in both processes. If you just fork+exec, you don't
214have to call it.</p> 225have to call it.</p>
215 <p>The function itself is quite fast and its usually not a problem to call 226 <p>The function itself is quite fast and it's usually not a problem to call
216it just in case after a fork. To make this easy, the function will fit in 227it just in case after a fork. To make this easy, the function will fit in
217quite nicely into a call to <code>pthread_atfork</code>:</p> 228quite nicely into a call to <code>pthread_atfork</code>:</p>
218<pre> pthread_atfork (0, 0, ev_default_fork); 229<pre> pthread_atfork (0, 0, ev_default_fork);
219 230
220</pre> 231</pre>
… …
228 <dt>unsigned int ev_method (loop)</dt> 239 <dt>unsigned int ev_method (loop)</dt>
229 <dd> 240 <dd>
230 <p>Returns one of the <code>EVMETHOD_*</code> flags indicating the event backend in 241 <p>Returns one of the <code>EVMETHOD_*</code> flags indicating the event backend in
231use.</p> 242use.</p>
232 </dd> 243 </dd>
233 <dt>ev_tstamp = ev_now (loop)</dt> 244 <dt>ev_tstamp ev_now (loop)</dt>
234 <dd> 245 <dd>
235 <p>Returns the current &quot;event loop time&quot;, which is the time the event loop 246 <p>Returns the current &quot;event loop time&quot;, which is the time the event loop
236got events and started processing them. This timestamp does not change 247got events and started processing them. This timestamp does not change
237as long as callbacks are being processed, and this is also the base time 248as long as callbacks are being processed, and this is also the base time
238used for relative timers. You can treat it as the timestamp of the event 249used for relative timers. You can treat it as the timestamp of the event
… …
245events.</p> 256events.</p>
246 <p>If the flags argument is specified as 0, it will not return until either 257 <p>If the flags argument is specified as 0, it will not return until either
247no event watchers are active anymore or <code>ev_unloop</code> was called.</p> 258no event watchers are active anymore or <code>ev_unloop</code> was called.</p>
248 <p>A flags value of <code>EVLOOP_NONBLOCK</code> will look for new events, will handle 259 <p>A flags value of <code>EVLOOP_NONBLOCK</code> will look for new events, will handle
249those events and any outstanding ones, but will not block your process in 260those events and any outstanding ones, but will not block your process in
250case there are no events.</p> 261case there are no events and will return after one iteration of the loop.</p>
251 <p>A flags value of <code>EVLOOP_ONESHOT</code> will look for new events (waiting if 262 <p>A flags value of <code>EVLOOP_ONESHOT</code> will look for new events (waiting if
252neccessary) and will handle those and any outstanding ones. It will block 263neccessary) and will handle those and any outstanding ones. It will block
253your process until at least one new event arrives.</p> 264your process until at least one new event arrives, and will return after
265one iteration of the loop.</p>
254 <p>This flags value could be used to implement alternative looping 266 <p>This flags value could be used to implement alternative looping
255constructs, but the <code>prepare</code> and <code>check</code> watchers provide a better and 267constructs, but the <code>prepare</code> and <code>check</code> watchers provide a better and
256more generic mechanism.</p> 268more generic mechanism.</p>
257 </dd> 269 </dd>
258 <dt>ev_unloop (loop, how)</dt> 270 <dt>ev_unloop (loop, how)</dt>
259 <dd> 271 <dd>
260 <p>Can be used to make a call to <code>ev_loop</code> return early. The <code>how</code> argument 272 <p>Can be used to make a call to <code>ev_loop</code> return early (but only after it
273has processed all outstanding events). The <code>how</code> argument must be either
261must be either <code>EVUNLOOP_ONCE</code>, which will make the innermost <code>ev_loop</code> 274<code>EVUNLOOP_ONCE</code>, which will make the innermost <code>ev_loop</code> call return, or
262call return, or <code>EVUNLOOP_ALL</code>, which will make all nested <code>ev_loop</code> 275<code>EVUNLOOP_ALL</code>, which will make all nested <code>ev_loop</code> calls return.</p>
263calls return.</p>
264 </dd> 276 </dd>
265 <dt>ev_ref (loop)</dt> 277 <dt>ev_ref (loop)</dt>
266 <dt>ev_unref (loop)</dt> 278 <dt>ev_unref (loop)</dt>
267 <dd> 279 <dd>
268 <p>Ref/unref can be used to add or remove a refcount on the event loop: Every 280 <p>Ref/unref can be used to add or remove a reference count on the event
269watcher keeps one reference. If you have a long-runing watcher you never 281loop: Every watcher keeps one reference, and as long as the reference
270unregister that should not keep ev_loop from running, ev_unref() after 282count is nonzero, <code>ev_loop</code> will not return on its own. If you have
271starting, and ev_ref() before stopping it. Libev itself uses this for 283a watcher you never unregister that should not keep <code>ev_loop</code> from
272example for its internal signal pipe: It is not visible to you as a user 284returning, ev_unref() after starting, and ev_ref() before stopping it. For
273and should not keep <code>ev_loop</code> from exiting if the work is done. It is 285example, libev itself uses this for its internal signal pipe: It is not
274also an excellent way to do this for generic recurring timers or from 286visible to the libev user and should not keep <code>ev_loop</code> from exiting if
275within third-party libraries. Just remember to unref after start and ref 287no event watchers registered by it are active. It is also an excellent
276before stop.</p> 288way to do this for generic recurring timers or from within third-party
289libraries. Just remember to <i>unref after start</i> and <i>ref before stop</i>.</p>
277 </dd> 290 </dd>
278</dl> 291</dl>
279 292
280</div> 293</div>
281<h1 id="ANATOMY_OF_A_WATCHER">ANATOMY OF A WATCHER</h1><p><a href="#TOP" class="toplink">Top</a></p> 294<h1 id="ANATOMY_OF_A_WATCHER">ANATOMY OF A WATCHER</h1><p><a href="#TOP" class="toplink">Top</a></p>
282<div id="ANATOMY_OF_A_WATCHER_CONTENT"> 295<div id="ANATOMY_OF_A_WATCHER_CONTENT">
283<p>A watcher is a structure that you create and register to record your 296<p>A watcher is a structure that you create and register to record your
284interest in some event. For instance, if you want to wait for STDIN to 297interest in some event. For instance, if you want to wait for STDIN to
285become readable, you would create an ev_io watcher for that:</p> 298become readable, you would create an <code>ev_io</code> watcher for that:</p>
286<pre> static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents) 299<pre> static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents)
287 { 300 {
288 ev_io_stop (w); 301 ev_io_stop (w);
289 ev_unloop (loop, EVUNLOOP_ALL); 302 ev_unloop (loop, EVUNLOOP_ALL);
290 } 303 }
… …
314*)</code>), and you can stop watching for events at any time by calling the 327*)</code>), and you can stop watching for events at any time by calling the
315corresponding stop function (<code>ev_&lt;type&gt;_stop (loop, watcher *)</code>.</p> 328corresponding stop function (<code>ev_&lt;type&gt;_stop (loop, watcher *)</code>.</p>
316<p>As long as your watcher is active (has been started but not stopped) you 329<p>As long as your watcher is active (has been started but not stopped) you
317must not touch the values stored in it. Most specifically you must never 330must not touch the values stored in it. Most specifically you must never
318reinitialise it or call its set method.</p> 331reinitialise it or call its set method.</p>
319<p>You cna check wether an event is active by calling the <code>ev_is_active 332<p>You can check whether an event is active by calling the <code>ev_is_active
320(watcher *)</code> macro. To see wether an event is outstanding (but the 333(watcher *)</code> macro. To see whether an event is outstanding (but the
321callback for it has not been called yet) you cna use the <code>ev_is_pending 334callback for it has not been called yet) you can use the <code>ev_is_pending
322(watcher *)</code> macro.</p> 335(watcher *)</code> macro.</p>
323<p>Each and every callback receives the event loop pointer as first, the 336<p>Each and every callback receives the event loop pointer as first, the
324registered watcher structure as second, and a bitset of received events as 337registered watcher structure as second, and a bitset of received events as
325third argument.</p> 338third argument.</p>
326<p>The rceeived events usually include a single bit per event type received 339<p>The received events usually include a single bit per event type received
327(you can receive multiple events at the same time). The possible bit masks 340(you can receive multiple events at the same time). The possible bit masks
328are:</p> 341are:</p>
329<dl> 342<dl>
330 <dt>EV_READ</dt> 343 <dt><code>EV_READ</code></dt>
331 <dt>EV_WRITE</dt> 344 <dt><code>EV_WRITE</code></dt>
332 <dd> 345 <dd>
333 <p>The file descriptor in the ev_io watcher has become readable and/or 346 <p>The file descriptor in the <code>ev_io</code> watcher has become readable and/or
334writable.</p> 347writable.</p>
335 </dd> 348 </dd>
336 <dt>EV_TIMEOUT</dt> 349 <dt><code>EV_TIMEOUT</code></dt>
337 <dd>
338 <p>The ev_timer watcher has timed out.</p>
339 </dd> 350 <dd>
340 <dt>EV_PERIODIC</dt> 351 <p>The <code>ev_timer</code> watcher has timed out.</p>
341 <dd> 352 </dd>
342 <p>The ev_periodic watcher has timed out.</p> 353 <dt><code>EV_PERIODIC</code></dt>
343 </dd> 354 <dd>
344 <dt>EV_SIGNAL</dt> 355 <p>The <code>ev_periodic</code> watcher has timed out.</p>
345 <dd> 356 </dd>
357 <dt><code>EV_SIGNAL</code></dt>
358 <dd>
346 <p>The signal specified in the ev_signal watcher has been received by a thread.</p> 359 <p>The signal specified in the <code>ev_signal</code> watcher has been received by a thread.</p>
347 </dd>
348 <dt>EV_CHILD</dt>
349 <dd> 360 </dd>
361 <dt><code>EV_CHILD</code></dt>
362 <dd>
350 <p>The pid specified in the ev_child watcher has received a status change.</p> 363 <p>The pid specified in the <code>ev_child</code> watcher has received a status change.</p>
351 </dd>
352 <dt>EV_IDLE</dt>
353 <dd> 364 </dd>
365 <dt><code>EV_IDLE</code></dt>
366 <dd>
354 <p>The ev_idle watcher has determined that you have nothing better to do.</p> 367 <p>The <code>ev_idle</code> watcher has determined that you have nothing better to do.</p>
355 </dd>
356 <dt>EV_PREPARE</dt>
357 <dt>EV_CHECK</dt>
358 <dd> 368 </dd>
369 <dt><code>EV_PREPARE</code></dt>
370 <dt><code>EV_CHECK</code></dt>
371 <dd>
359 <p>All ev_prepare watchers are invoked just <i>before</i> <code>ev_loop</code> starts 372 <p>All <code>ev_prepare</code> watchers are invoked just <i>before</i> <code>ev_loop</code> starts
360to gather new events, and all ev_check watchers are invoked just after 373to gather new events, and all <code>ev_check</code> watchers are invoked just after
361<code>ev_loop</code> has gathered them, but before it invokes any callbacks for any 374<code>ev_loop</code> has gathered them, but before it invokes any callbacks for any
362received events. Callbacks of both watcher types can start and stop as 375received events. Callbacks of both watcher types can start and stop as
363many watchers as they want, and all of them will be taken into account 376many watchers as they want, and all of them will be taken into account
364(for example, a ev_prepare watcher might start an idle watcher to keep 377(for example, a <code>ev_prepare</code> watcher might start an idle watcher to keep
365<code>ev_loop</code> from blocking).</p> 378<code>ev_loop</code> from blocking).</p>
366 </dd> 379 </dd>
367 <dt>EV_ERROR</dt> 380 <dt><code>EV_ERROR</code></dt>
368 <dd> 381 <dd>
369 <p>An unspecified error has occured, the watcher has been stopped. This might 382 <p>An unspecified error has occured, the watcher has been stopped. This might
370happen because the watcher could not be properly started because libev 383happen because the watcher could not be properly started because libev
371ran out of memory, a file descriptor was found to be closed or any other 384ran out of memory, a file descriptor was found to be closed or any other
372problem. You best act on it by reporting the problem and somehow coping 385problem. You best act on it by reporting the problem and somehow coping
… …
381 394
382</div> 395</div>
383<h2 id="ASSOCIATING_CUSTOM_DATA_WITH_A_WATCH">ASSOCIATING CUSTOM DATA WITH A WATCHER</h2> 396<h2 id="ASSOCIATING_CUSTOM_DATA_WITH_A_WATCH">ASSOCIATING CUSTOM DATA WITH A WATCHER</h2>
384<div id="ASSOCIATING_CUSTOM_DATA_WITH_A_WATCH-2"> 397<div id="ASSOCIATING_CUSTOM_DATA_WITH_A_WATCH-2">
385<p>Each watcher has, by default, a member <code>void *data</code> that you can change 398<p>Each watcher has, by default, a member <code>void *data</code> that you can change
386and read at any time, libev will completely ignore it. This cna be used 399and read at any time, libev will completely ignore it. This can be used
387to associate arbitrary data with your watcher. If you need more data and 400to associate arbitrary data with your watcher. If you need more data and
388don't want to allocate memory and store a pointer to it in that data 401don't want to allocate memory and store a pointer to it in that data
389member, you can also &quot;subclass&quot; the watcher type and provide your own 402member, you can also &quot;subclass&quot; the watcher type and provide your own
390data:</p> 403data:</p>
391<pre> struct my_io 404<pre> struct my_io
… …
418<div id="WATCHER_TYPES_CONTENT"> 431<div id="WATCHER_TYPES_CONTENT">
419<p>This section describes each watcher in detail, but will not repeat 432<p>This section describes each watcher in detail, but will not repeat
420information given in the last section.</p> 433information given in the last section.</p>
421 434
422</div> 435</div>
423<h2 id="struct_ev_io_is_my_file_descriptor_r">struct ev_io - is my file descriptor readable or writable</h2> 436<h2 id="code_ev_io_code_is_this_file_descrip"><code>ev_io</code> - is this file descriptor readable or writable</h2>
424<div id="struct_ev_io_is_my_file_descriptor_r-2"> 437<div id="code_ev_io_code_is_this_file_descrip-2">
425<p>I/O watchers check wether a file descriptor is readable or writable 438<p>I/O watchers check whether a file descriptor is readable or writable
426in each iteration of the event loop (This behaviour is called 439in each iteration of the event loop (This behaviour is called
427level-triggering because you keep receiving events as long as the 440level-triggering because you keep receiving events as long as the
428condition persists. Remember you cna stop the watcher if you don't want to 441condition persists. Remember you can stop the watcher if you don't want to
429act on the event and neither want to receive future events).</p> 442act 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
444fd 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
446required if you know what you are doing).</p>
447<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
449descriptors correctly if you register interest in two or more fds pointing
450to the same file/socket etc. description.</p>
451<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
453EVMETHOD_POLL).</p>
430<dl> 454<dl>
431 <dt>ev_io_init (ev_io *, callback, int fd, int events)</dt> 455 <dt>ev_io_init (ev_io *, callback, int fd, int events)</dt>
432 <dt>ev_io_set (ev_io *, int fd, int events)</dt> 456 <dt>ev_io_set (ev_io *, int fd, int events)</dt>
433 <dd> 457 <dd>
434 <p>Configures an ev_io watcher. The fd is the file descriptor to rceeive 458 <p>Configures an <code>ev_io</code> watcher. The fd is the file descriptor to rceeive
435events for and events is either <code>EV_READ</code>, <code>EV_WRITE</code> or <code>EV_READ | 459events for and events is either <code>EV_READ</code>, <code>EV_WRITE</code> or <code>EV_READ |
436EV_WRITE</code> to receive the given events.</p> 460EV_WRITE</code> to receive the given events.</p>
437 </dd> 461 </dd>
438</dl> 462</dl>
439 463
440</div> 464</div>
441<h2 id="struct_ev_timer_relative_and_optiona">struct ev_timer - relative and optionally recurring timeouts</h2> 465<h2 id="code_ev_timer_code_relative_and_opti"><code>ev_timer</code> - relative and optionally recurring timeouts</h2>
442<div id="struct_ev_timer_relative_and_optiona-2"> 466<div id="code_ev_timer_code_relative_and_opti-2">
443<p>Timer watchers are simple relative timers that generate an event after a 467<p>Timer watchers are simple relative timers that generate an event after a
444given time, and optionally repeating in regular intervals after that.</p> 468given time, and optionally repeating in regular intervals after that.</p>
445<p>The timers are based on real time, that is, if you register an event that 469<p>The timers are based on real time, that is, if you register an event that
446times out after an hour and youreset your system clock to last years 470times out after an hour and youreset your system clock to last years
447time, it will still time out after (roughly) and hour. &quot;Roughly&quot; because 471time, it will still time out after (roughly) and hour. &quot;Roughly&quot; because
448detecting time jumps is hard, and soem inaccuracies are unavoidable (the 472detecting time jumps is hard, and soem inaccuracies are unavoidable (the
449monotonic clock option helps a lot here).</p> 473monotonic clock option helps a lot here).</p>
474<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
476of the event triggering whatever timeout you are modifying/starting. If
477you 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>
479<pre> ev_timer_set (&amp;timer, after + ev_now () - ev_time (), 0.);
480
481</pre>
450<dl> 482<dl>
451 <dt>ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)</dt> 483 <dt>ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)</dt>
452 <dt>ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)</dt> 484 <dt>ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)</dt>
453 <dd> 485 <dd>
454 <p>Configure the timer to trigger after <code>after</code> seconds. If <code>repeat</code> is 486 <p>Configure the timer to trigger after <code>after</code> seconds. If <code>repeat</code> is
… …
470value), or reset the running timer to the repeat value.</p> 502value), or reset the running timer to the repeat value.</p>
471 <p>This sounds a bit complicated, but here is a useful and typical 503 <p>This sounds a bit complicated, but here is a useful and typical
472example: Imagine you have a tcp connection and you want a so-called idle 504example: Imagine you have a tcp connection and you want a so-called idle
473timeout, that is, you want to be called when there have been, say, 60 505timeout, that is, you want to be called when there have been, say, 60
474seconds of inactivity on the socket. The easiest way to do this is to 506seconds of inactivity on the socket. The easiest way to do this is to
475configure an ev_timer with after=repeat=60 and calling ev_timer_again each 507configure an <code>ev_timer</code> with after=repeat=60 and calling ev_timer_again each
476time you successfully read or write some data. If you go into an idle 508time you successfully read or write some data. If you go into an idle
477state where you do not expect data to travel on the socket, you can stop 509state where you do not expect data to travel on the socket, you can stop
478the timer, and again will automatically restart it if need be.</p> 510the timer, and again will automatically restart it if need be.</p>
479 </dd> 511 </dd>
480</dl> 512</dl>
481 513
482</div> 514</div>
483<h2 id="ev_periodic">ev_periodic</h2> 515<h2 id="code_ev_periodic_code_to_cron_or_not"><code>ev_periodic</code> - to cron or not to cron</h2>
484<div id="ev_periodic_CONTENT"> 516<div id="code_ev_periodic_code_to_cron_or_not-2">
485<p>Periodic watchers are also timers of a kind, but they are very versatile 517<p>Periodic watchers are also timers of a kind, but they are very versatile
486(and unfortunately a bit complex).</p> 518(and unfortunately a bit complex).</p>
487<p>Unlike ev_timer's, they are not based on real time (or relative time) 519<p>Unlike <code>ev_timer</code>'s, they are not based on real time (or relative time)
488but on wallclock time (absolute time). You can tell a periodic watcher 520but on wallclock time (absolute time). You can tell a periodic watcher
489to trigger &quot;at&quot; some specific point in time. For example, if you tell a 521to trigger &quot;at&quot; some specific point in time. For example, if you tell a
490periodic watcher to trigger in 10 seconds (by specifiying e.g. c&lt;ev_now () 522periodic watcher to trigger in 10 seconds (by specifiying e.g. c&lt;ev_now ()
491+ 10.&gt;) and then reset your system clock to the last year, then it will 523+ 10.&gt;) and then reset your system clock to the last year, then it will
492take a year to trigger the event (unlike an ev_timer, which would trigger 524take a year to trigger the event (unlike an <code>ev_timer</code>, which would trigger
493roughly 10 seconds later and of course not if you reset your system time 525roughly 10 seconds later and of course not if you reset your system time
494again).</p> 526again).</p>
495<p>They can also be used to implement vastly more complex timers, such as 527<p>They can also be used to implement vastly more complex timers, such as
496triggering an event on eahc midnight, local time.</p> 528triggering an event on eahc midnight, local time.</p>
497<dl> 529<dl>
… …
523<pre> ev_periodic_set (&amp;periodic, 0., 3600., 0); 555<pre> ev_periodic_set (&amp;periodic, 0., 3600., 0);
524 556
525</pre> 557</pre>
526 <p>This doesn't mean there will always be 3600 seconds in between triggers, 558 <p>This doesn't mean there will always be 3600 seconds in between triggers,
527but only that the the callback will be called when the system time shows a 559but only that the the callback will be called when the system time shows a
528full hour (UTC), or more correct, when the system time is evenly divisible 560full hour (UTC), or more correctly, when the system time is evenly divisible
529by 3600.</p> 561by 3600.</p>
530 <p>Another way to think about it (for the mathematically inclined) is that 562 <p>Another way to think about it (for the mathematically inclined) is that
531ev_periodic will try to run the callback in this mode at the next possible 563<code>ev_periodic</code> will try to run the callback in this mode at the next possible
532time where <code>time = at (mod interval)</code>, regardless of any time jumps.</p> 564time where <code>time = at (mod interval)</code>, regardless of any time jumps.</p>
533 </dd> 565 </dd>
534 <dt>* manual reschedule mode (reschedule_cb = callback)</dt> 566 <dt>* manual reschedule mode (reschedule_cb = callback)</dt>
535 <dd> 567 <dd>
536 <p>In this mode the values for <code>interval</code> and <code>at</code> are both being 568 <p>In this mode the values for <code>interval</code> and <code>at</code> are both being
537ignored. Instead, each time the periodic watcher gets scheduled, the 569ignored. Instead, each time the periodic watcher gets scheduled, the
538reschedule callback will be called with the watcher as first, and the 570reschedule callback will be called with the watcher as first, and the
539current time as second argument.</p> 571current time as second argument.</p>
540 <p>NOTE: <i>This callback MUST NOT stop or destroy the periodic or any other 572 <p>NOTE: <i>This callback MUST NOT stop or destroy the periodic or any other
541periodic watcher, ever, or make any event loop modificstions</i>. If you need 573periodic watcher, ever, or make any event loop modifications</i>. If you need
542to stop it, return 1e30 (or so, fudge fudge) and stop it afterwards.</p> 574to stop it, return <code>now + 1e30</code> (or so, fudge fudge) and stop it afterwards.</p>
575 <p>Also, <i>this callback must always return a time that is later than the
576passed <code>now</code> value</i>. Not even <code>now</code> itself will be ok.</p>
543 <p>Its prototype is c&lt;ev_tstamp (*reschedule_cb)(struct ev_periodic *w, 577 <p>Its prototype is <code>ev_tstamp (*reschedule_cb)(struct ev_periodic *w,
544ev_tstamp now)&gt;, e.g.:</p> 578ev_tstamp now)</code>, e.g.:</p>
545<pre> static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now) 579<pre> static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)
546 { 580 {
547 return now + 60.; 581 return now + 60.;
548 } 582 }
549 583
… …
568program when the crontabs have changed).</p> 602program when the crontabs have changed).</p>
569 </dd> 603 </dd>
570</dl> 604</dl>
571 605
572</div> 606</div>
573<h2 id="ev_signal_signal_me_when_a_signal_ge">ev_signal - signal me when a signal gets signalled</h2> 607<h2 id="code_ev_signal_code_signal_me_when_a"><code>ev_signal</code> - signal me when a signal gets signalled</h2>
574<div id="ev_signal_signal_me_when_a_signal_ge-2"> 608<div id="code_ev_signal_code_signal_me_when_a-2">
575<p>Signal watchers will trigger an event when the process receives a specific 609<p>Signal watchers will trigger an event when the process receives a specific
576signal one or more times. Even though signals are very asynchronous, libev 610signal one or more times. Even though signals are very asynchronous, libev
577will try its best to deliver signals synchronously, i.e. as part of the 611will try it's best to deliver signals synchronously, i.e. as part of the
578normal event processing, like any other event.</p> 612normal event processing, like any other event.</p>
579<p>You cna configure as many watchers as you like per signal. Only when the 613<p>You can configure as many watchers as you like per signal. Only when the
580first watcher gets started will libev actually register a signal watcher 614first watcher gets started will libev actually register a signal watcher
581with the kernel (thus it coexists with your own signal handlers as long 615with the kernel (thus it coexists with your own signal handlers as long
582as you don't register any with libev). Similarly, when the last signal 616as you don't register any with libev). Similarly, when the last signal
583watcher for a signal is stopped libev will reset the signal handler to 617watcher for a signal is stopped libev will reset the signal handler to
584SIG_DFL (regardless of what it was set to before).</p> 618SIG_DFL (regardless of what it was set to before).</p>
… …
590of the <code>SIGxxx</code> constants).</p> 624of the <code>SIGxxx</code> constants).</p>
591 </dd> 625 </dd>
592</dl> 626</dl>
593 627
594</div> 628</div>
595<h2 id="ev_child_wait_for_pid_status_changes">ev_child - wait for pid status changes</h2> 629<h2 id="code_ev_child_code_wait_for_pid_stat"><code>ev_child</code> - wait for pid status changes</h2>
596<div id="ev_child_wait_for_pid_status_changes-2"> 630<div id="code_ev_child_code_wait_for_pid_stat-2">
597<p>Child watchers trigger when your process receives a SIGCHLD in response to 631<p>Child watchers trigger when your process receives a SIGCHLD in response to
598some child status changes (most typically when a child of yours dies).</p> 632some child status changes (most typically when a child of yours dies).</p>
599<dl> 633<dl>
600 <dt>ev_child_init (ev_child *, callback, int pid)</dt> 634 <dt>ev_child_init (ev_child *, callback, int pid)</dt>
601 <dt>ev_child_set (ev_child *, int pid)</dt> 635 <dt>ev_child_set (ev_child *, int pid)</dt>
602 <dd> 636 <dd>
603 <p>Configures the watcher to wait for status changes of process <code>pid</code> (or 637 <p>Configures the watcher to wait for status changes of process <code>pid</code> (or
604<i>any</i> process if <code>pid</code> is specified as <code>0</code>). The callback can look 638<i>any</i> process if <code>pid</code> is specified as <code>0</code>). The callback can look
605at the <code>rstatus</code> member of the <code>ev_child</code> watcher structure to see 639at the <code>rstatus</code> member of the <code>ev_child</code> watcher structure to see
606the status word (use the macros from <code>sys/wait.h</code>). The <code>rpid</code> member 640the status word (use the macros from <code>sys/wait.h</code> and see your systems
641<code>waitpid</code> documentation). The <code>rpid</code> member contains the pid of the
607contains the pid of the process causing the status change.</p> 642process causing the status change.</p>
608 </dd> 643 </dd>
609</dl> 644</dl>
610 645
611</div> 646</div>
612<h2 id="ev_idle_when_you_ve_got_nothing_bett">ev_idle - when you've got nothing better to do</h2> 647<h2 id="code_ev_idle_code_when_you_ve_got_no"><code>ev_idle</code> - when you've got nothing better to do</h2>
613<div id="ev_idle_when_you_ve_got_nothing_bett-2"> 648<div id="code_ev_idle_code_when_you_ve_got_no-2">
614<p>Idle watchers trigger events when there are no other I/O or timer (or 649<p>Idle watchers trigger events when there are no other events are pending
615periodic) events pending. That is, as long as your process is busy 650(prepare, check and other idle watchers do not count). That is, as long
616handling sockets or timeouts it will not be called. But when your process 651as your process is busy handling sockets or timeouts (or even signals,
617is idle all idle watchers are being called again and again - until 652imagine) it will not be triggered. But when your process is idle all idle
653watchers are being called again and again, once per event loop iteration -
618stopped, that is, or your process receives more events.</p> 654until stopped, that is, or your process receives more events and becomes
655busy.</p>
619<p>The most noteworthy effect is that as long as any idle watchers are 656<p>The most noteworthy effect is that as long as any idle watchers are
620active, the process will not block when waiting for new events.</p> 657active, the process will not block when waiting for new events.</p>
621<p>Apart from keeping your process non-blocking (which is a useful 658<p>Apart from keeping your process non-blocking (which is a useful
622effect on its own sometimes), idle watchers are a good place to do 659effect on its own sometimes), idle watchers are a good place to do
623&quot;pseudo-background processing&quot;, or delay processing stuff to after the 660&quot;pseudo-background processing&quot;, or delay processing stuff to after the
… …
630believe me.</p> 667believe me.</p>
631 </dd> 668 </dd>
632</dl> 669</dl>
633 670
634</div> 671</div>
635<h2 id="prepare_and_check_your_hooks_into_th">prepare and check - your hooks into the event loop</h2> 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>
636<div id="prepare_and_check_your_hooks_into_th-2"> 673<div id="code_ev_prepare_code_and_code_ev_che-2">
637<p>Prepare and check watchers usually (but not always) are used in 674<p>Prepare and check watchers are usually (but not always) used in tandem:
638tandom. Prepare watchers get invoked before the process blocks and check 675Prepare watchers get invoked before the process blocks and check watchers
639watchers afterwards.</p> 676afterwards.</p>
640<p>Their main purpose is to integrate other event mechanisms into libev. This 677<p>Their main purpose is to integrate other event mechanisms into libev. This
641could be used, for example, to track variable changes, implement your own 678could be used, for example, to track variable changes, implement your own
642watchers, integrate net-snmp or a coroutine library and lots more.</p> 679watchers, integrate net-snmp or a coroutine library and lots more.</p>
643<p>This is done by examining in each prepare call which file descriptors need 680<p>This is done by examining in each prepare call which file descriptors need
644to be watched by the other library, registering ev_io watchers for them 681to be watched by the other library, registering <code>ev_io</code> watchers for
645and starting an ev_timer watcher for any timeouts (many libraries provide 682them and starting an <code>ev_timer</code> watcher for any timeouts (many libraries
646just this functionality). Then, in the check watcher you check for any 683provide just this functionality). Then, in the check watcher you check for
647events that occured (by making your callbacks set soem flags for example) 684any events that occured (by checking the pending status of all watchers
648and call back into the library.</p> 685and stopping them) and call back into the library. The I/O and timer
686callbacks will never actually be called (but must be valid neverthelles,
687because you never know, you know?).</p>
649<p>As another example, the perl Coro module uses these hooks to integrate 688<p>As another example, the Perl Coro module uses these hooks to integrate
650coroutines into libev programs, by yielding to other active coroutines 689coroutines into libev programs, by yielding to other active coroutines
651during each prepare and only letting the process block if no coroutines 690during each prepare and only letting the process block if no coroutines
652are ready to run.</p> 691are ready to run (its actually more complicated, it only runs coroutines
692with priority higher than the event loop and one lower priority once,
693using idle watchers to keep the event loop from blocking if lower-priority
694coroutines exist, thus mapping low-priority coroutines to idle/background
695tasks).</p>
653<dl> 696<dl>
654 <dt>ev_prepare_init (ev_prepare *, callback)</dt> 697 <dt>ev_prepare_init (ev_prepare *, callback)</dt>
655 <dt>ev_check_init (ev_check *, callback)</dt> 698 <dt>ev_check_init (ev_check *, callback)</dt>
656 <dd> 699 <dd>
657 <p>Initialises and configures the prepare or check watcher - they have no 700 <p>Initialises and configures the prepare or check watcher - they have no
658parameters of any kind. There are <code>ev_prepare_set</code> and <code>ev_check_set</code> 701parameters of any kind. There are <code>ev_prepare_set</code> and <code>ev_check_set</code>
659macros, but using them is utterly, utterly pointless.</p> 702macros, but using them is utterly, utterly and completely pointless.</p>
660 </dd> 703 </dd>
661</dl> 704</dl>
662 705
663</div> 706</div>
664<h1 id="OTHER_FUNCTIONS">OTHER FUNCTIONS</h1><p><a href="#TOP" class="toplink">Top</a></p> 707<h1 id="OTHER_FUNCTIONS">OTHER FUNCTIONS</h1><p><a href="#TOP" class="toplink">Top</a></p>
665<div id="OTHER_FUNCTIONS_CONTENT"> 708<div id="OTHER_FUNCTIONS_CONTENT">
666<p>There are some other fucntions of possible interest. Described. Here. Now.</p> 709<p>There are some other functions of possible interest. Described. Here. Now.</p>
667<dl> 710<dl>
668 <dt>ev_once (loop, int fd, int events, ev_tstamp timeout, callback)</dt> 711 <dt>ev_once (loop, int fd, int events, ev_tstamp timeout, callback)</dt>
669 <dd> 712 <dd>
670 <p>This function combines a simple timer and an I/O watcher, calls your 713 <p>This function combines a simple timer and an I/O watcher, calls your
671callback on whichever event happens first and automatically stop both 714callback on whichever event happens first and automatically stop both
672watchers. This is useful if you want to wait for a single event on an fd 715watchers. This is useful if you want to wait for a single event on an fd
673or timeout without havign to allocate/configure/start/stop/free one or 716or timeout without havign to allocate/configure/start/stop/free one or
674more watchers yourself.</p> 717more watchers yourself.</p>
675 <p>If <code>fd</code> is less than 0, then no I/O watcher will be started and events is 718 <p>If <code>fd</code> is less than 0, then no I/O watcher will be started and events
676ignored. Otherwise, an ev_io watcher for the given <code>fd</code> and <code>events</code> set 719is being ignored. Otherwise, an <code>ev_io</code> watcher for the given <code>fd</code> and
677will be craeted and started.</p> 720<code>events</code> set will be craeted and started.</p>
678 <p>If <code>timeout</code> is less than 0, then no timeout watcher will be 721 <p>If <code>timeout</code> is less than 0, then no timeout watcher will be
679started. Otherwise an ev_timer watcher with after = <code>timeout</code> (and repeat 722started. Otherwise an <code>ev_timer</code> watcher with after = <code>timeout</code> (and
680= 0) will be started.</p> 723repeat = 0) will be started. While <code>0</code> is a valid timeout, it is of
724dubious value.</p>
681 <p>The callback has the type <code>void (*cb)(int revents, void *arg)</code> and 725 <p>The callback has the type <code>void (*cb)(int revents, void *arg)</code> and gets
682gets passed an events set (normally a combination of EV_ERROR, EV_READ, 726passed an events set like normal event callbacks (with a combination of
683EV_WRITE or EV_TIMEOUT) and the <code>arg</code> value passed to <code>ev_once</code>:</p> 727<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>
684<pre> static void stdin_ready (int revents, void *arg) 729<pre> static void stdin_ready (int revents, void *arg)
685 { 730 {
686 if (revents &amp; EV_TIMEOUT) 731 if (revents &amp; EV_TIMEOUT)
687 /* doh, nothing entered */ 732 /* doh, nothing entered */;
688 else if (revents &amp; EV_READ) 733 else if (revents &amp; EV_READ)
689 /* stdin might have data for us, joy! */ 734 /* stdin might have data for us, joy! */;
690 } 735 }
691 736
692 ev_once (STDIN_FILENO, EV_READm 10., stdin_ready, 0); 737 ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
693 738
694</pre> 739</pre>
695 </dd> 740 </dd>
696 <dt>ev_feed_event (loop, watcher, int events)</dt> 741 <dt>ev_feed_event (loop, watcher, int events)</dt>
697 <dd> 742 <dd>
698 <p>Feeds the given event set into the event loop, as if the specified event 743 <p>Feeds the given event set into the event loop, as if the specified event
699has happened for the specified watcher (which must be a pointer to an 744had happened for the specified watcher (which must be a pointer to an
700initialised but not necessarily active event watcher).</p> 745initialised but not necessarily started event watcher).</p>
701 </dd> 746 </dd>
702 <dt>ev_feed_fd_event (loop, int fd, int revents)</dt> 747 <dt>ev_feed_fd_event (loop, int fd, int revents)</dt>
703 <dd> 748 <dd>
704 <p>Feed an event on the given fd, as if a file descriptor backend detected it.</p> 749 <p>Feed an event on the given fd, as if a file descriptor backend detected
750the given events it.</p>
705 </dd> 751 </dd>
706 <dt>ev_feed_signal_event (loop, int signum)</dt> 752 <dt>ev_feed_signal_event (loop, int signum)</dt>
707 <dd> 753 <dd>
708 <p>Feed an event as if the given signal occured (loop must be the default loop!).</p> 754 <p>Feed an event as if the given signal occured (loop must be the default loop!).</p>
709 </dd> 755 </dd>

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