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<h1>Watcher callbacks</h1>
<p class="para">
All watchers can be active(waiting for events) or inactive(paused). Only
active watchers will have their callbacks invoked. All callbacks will be
called with at least two arguments:
<em><code class="parameter">watcher</code></em>
- the watcher, and
<em><code class="parameter">revents</code></em>
a bitmask of received events.
</p>
<p class="para">
Watcher callbacks are passed to the watcher contructors(the classes derived
from
<a href="class.evwatcher.html" class="classname">EvWatcher</a>
-
<span class="methodname"><a href="evcheck.construct.html" class="methodname">EvCheck::__construct()</a></span>
,
<span class="methodname"><a href="evchild.construct.html" class="methodname">EvChild::__construct()</a></span>
etc.). A watcher callback should match the following prototype:
</p>
<div class="methodsynopsis dc-description">
<span class="type"><span class="type void">void</span></span>
<span class="methodname"><strong>callback</strong></span>
([ <span class="methodparam">
<span class="type">object</span>
<code class="parameter">$watcher</code>
<span class="initializer"> = NULL</span>
</span>
[, <span class="methodparam">
<span class="type">int</span>
<code class="parameter">$revents</code>
<span class="initializer"> = NULL</span>
</span>
]] )</div>
<p class="para">
<dl>
<dt>
<span class="term">
<em><code class="parameter">watcher</code></em>
</span>
<dd>
<p class="para">
The watcher instance(of a class extending
<a href="class.evwatcher.html" class="classname">EvWatcher</a>
).
</p>
</dd>
</dt>
<dt>
<span class="term">
<em><code class="parameter">revents</code></em>
</span>
<dd>
<p class="para">
<a href="class.ev.html#ev.constants.watcher-revents" class="link">Watcher received events</a>
.
</p>
</dd>
</dt>
</dl>
</p>
<p class="para">
Each watcher type has its associated bit in
<em><code class="parameter">revents</code></em>
, so one can use the same callback for multiple watchers. The event mask is
named after the type, i.e.
<a href="class.evchild.html" class="classname">EvChild</a>
(or
<span class="methodname"><a href="evloop.child.html" class="methodname">EvLoop::child()</a></span>
) sets
<strong><code>EV::CHILD</code></strong>
,
<a href="class.evprepare.html" class="classname">EvPrepare</a>
(or
<span class="methodname"><a href="evloop.prepare.html" class="methodname">EvLoop::prepare()</a></span>
) sets
<strong><code>Ev::PREPARE</code></strong>
,
<a href="class.evperiodic.html" class="classname">EvPeriodic</a>
(or
<span class="methodname"><a href="evloop.periodic.html" class="methodname">EvLoop::periodic()</a></span>
) sets
<strong><code>Ev::PERIODIC</code></strong>
and so on, with the exception of I/O events (which can set both
<strong><code>Ev::READ</code></strong>
and
<strong><code>Ev::WRITE</code></strong>
bits).
</p>
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