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<?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>
Prior to PHP 8.4.0, switching fibers during the execution of an object
<link linkend="language.oop5.decon.destructor">destructor</link> was not
allowed.
</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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sgml-parent-document:nil
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