fibers.xml

<?xml version="1.0" encoding="utf-8"?>
<chapter xml:id="language.fibers" xmlns="http://docbook.org/ns/docbook">
 <title>Fibers</title>

 <simplesect xml:id="language.fibers.overview">
  <title>Fibers overview</title>
  <?phpdoc print-version-for="fiber"?>
  <para>
   Fibers represent full-stack, interruptible functions. Fibers may be suspended from anywhere in the call-stack,
   pausing execution within the fiber until the fiber is resumed at a later time.
  </para>
  <para>
   Fibers pause the entire execution stack, so the direct caller of the function does not need to change how it
   invokes the function.
  </para>
  <para>
   Execution may be interrupted anywhere in the call stack using <methodname>Fiber::suspend</methodname>
   (that is, the call to <methodname>Fiber::suspend</methodname> may be in a deeply nested function or not
   even exist at all).
  </para>
  <para>
   Unlike stack-less <classname>Generator</classname>s, each <classname>Fiber</classname> has its own call stack,
   allowing them to be paused within deeply nested function calls. A function declaring an interruption point
   (that is, calling <methodname>Fiber::suspend</methodname>) need not change its return type, unlike a function using
   &yield; which must return a <classname>Generator</classname> instance.
  </para>
  <para>
   Fibers can be suspended in any function call, including those called from within the PHP VM, such as functions
   provided to <function>array_map</function> or methods called by foreach on an
   <classname>Iterator</classname> object.
  </para>
  <para>
   Once suspended, execution of the fiber may be resumed with any value using <methodname>Fiber::resume</methodname>
   or by throwing an exception into the fiber using <methodname>Fiber::throw</methodname>. The value is returned
   (or exception thrown) from <methodname>Fiber::suspend</methodname>.
  </para>
  <note>
   <simpara>
    Due to current limitations it is not possible to switch fibers in the destructor of an object.
   </simpara>
  </note> 

  <example xml:id="language.fiber.example.basic"><!-- {{{ -->
   <title>Basic usage</title>
   <programlisting role="php">
    <![CDATA[
<?php
$fiber = new Fiber(function (): void {
   $value = Fiber::suspend('fiber');
   echo "Value used to resume fiber: ", $value, PHP_EOL;
});

$value = $fiber->start();

echo "Value from fiber suspending: ", $value, PHP_EOL;

$fiber->resume('test');
?>
]]>
   </programlisting>
   &example.outputs;
   <screen>
    <![CDATA[
Value from fiber suspending: fiber
Value used to resume fiber: test
]]>
   </screen>
  </example><!-- }}} -->

 </simplesect>

</chapter>
 
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