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<h1>About event persistence</h1>
<p class="para">
By default, whenever a pending event becomes active (because its file
descriptor is ready to read or write, or because its timeout expires), it
becomes non-pending right before its callback is executed. Thus, to make the
event pending again one may call
<span class="methodname"><a href="event.add.html" class="methodname">Event::add()</a></span>
on it again from inside the callback function.
</p>
<p class="para">
If the
<strong><code>Event::PERSIST</code></strong>
flag is set on an event, however, the event is
<em class="emphasis">persistent</em>
. This means that event remains pending even when its callback is activated.
<span class="methodname"><a href="event.del.html" class="methodname">Event::del()</a></span>
method can be called to make it non-pending.
</p>
<p class="para">
The timeout on a persistent event resets whenever the event's callback runs.
Thus, if one has an event with flags
<strong><code>Event::READ</code></strong>
<em>|</em>
<strong><code>Event::PERSIST</code></strong>
and a timeout of five seconds, the event will become active:
</p>
<ol type="1">
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<p class="para">
Whenever the socket or file descriptor is ready for reading.
</p>
</li>
<li class="listitem">
<p class="para">
Whenever five seconds have passed since the event last became active.
</p>
</li>
</ol>
<p class="para">
See also
<a href="http://www.wangafu.net/~nickm/libevent-book/Ref4_event.html#_about_event_persistence" class="link external">» Fast
portable non-blocking network programming with Libevent, About Event
Persistence</a>
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