php-doc-en/reference/ev/watchers.xml

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<chapter  xml:id="ev.watchers" xmlns:phpdoc="http://php.net/ns/phpdoc" xmlns="http://docbook.org/ns/docbook" xmlns:xlink="http://www.w3.org/1999/xlink">
 <title>Watchers</title>
 <para>
  A watcher is an object that gets created to record interest in some event.
  For instance, the following code waits for
  <constant>STDIN</constant>
  to become readable:
  <programlisting role="php">
<![CDATA[
<?php
// Wait until STDIN is readable
$w = new EvIo(STDIN, Ev::READ, function ($watcher, $revents) {
 echo "STDIN is readable\n";
});
Ev::run(Ev::RUN_ONCE);
?>
]]>
  </programlisting>
 </para>
 <para>
  All the watcher constructors automatically start the watchers.
  <literal>createStopped</literal>
  methods create stopped watchers(e.g.
  <methodname>EvIo::createStopped</methodname>
  )
 </para>
 <para>
  Note that a watcher will automatically be stopped when the watcher object is
  destroyed. Therefore, the watcher objects returned by the constructors or
  factory methods should be kept.
 </para>
 <para>
  Note also that all methods changing some watcher property(
  <emphasis>set</emphasis>
  ,
  <varname>priority</varname>
  etc.) automatically stop and start it again if it is active, which means
  pending events get lost.
 </para>
 <para>
  See also:
  <link linkend="ev.watcher-callbacks">Watcher callbacks</link>
  .
 </para>
</chapter>
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