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<?xml version="1.0" encoding="utf-8"?>
<!-- $Revision$ -->
<book xml:id="book.parallel" xmlns="http://docbook.org/ns/docbook" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:xi="http://www.w3.org/2001/XInclude">
<?phpdoc extension-membership="pecl" ?>
<title>parallel</title>
<titleabbrev>parallel</titleabbrev>
<preface xml:id="intro.parallel">
&reftitle.intro;
<para>
parallel is a parallel concurrency extension for PHP ≥ 7.2.0.
As of parallel 1.2.0, PHP ≥ 8.0.0 is required.
</para>
<para>
A brief description of the concepts core to parallel follows, more detailed information may be found within this section of the manual.
</para>
<simplesect>
<title>Runtime</title>
<para>
A <classname>parallel\Runtime</classname> represents a PHP interpreter thread. A <classname>parallel\Runtime</classname> is configured with an optional bootstrap file passed to <methodname>parallel\Runtime::__construct</methodname>, this is typically an autoloader,
or some other preloading routine: The bootstrap file will be included before any task is executed.
</para>
<para>
After construction the <classname>parallel\Runtime</classname> remains available until it is closed, killed, or destroyed by the normal scoping rules of PHP objects.
<methodname>parallel\Runtime::run</methodname> allows the programmer to schedule tasks for execution in parallel.
A <classname>parallel\Runtime</classname> has a FIFO schedule, tasks will be executed in the order that they are scheduled.
</para>
</simplesect>
<simplesect>
<title>Functional API</title>
<para>
parallel implements a functional, higher level API on top of <classname>parallel\Runtime</classname> that provides a single function entry point to executing parallel code
with automatic scheduling: <function>parallel\run</function>.
</para>
</simplesect>
<simplesect>
<title>Task</title>
<para>
A task is simply a <classname>Closure</classname> intended for parallel execution. The <classname>Closure</classname> may contain almost any instruction, including nested closures.
However, there are some instructions that are prohibited in tasks:
<itemizedlist>
<listitem>
<para>yield</para>
</listitem>
<listitem>
<para>use by-reference</para>
</listitem>
<listitem>
<para>declare class</para>
</listitem>
<listitem>
<para>declare named function</para>
</listitem>
</itemizedlist>
</para>
<note>
<para>
Nested closures may yield or use by-reference, but must not contain class or named function declarations.
</para>
</note>
<note>
<para>
No instructions are prohibited in the files which the task may include.
</para>
</note>
</simplesect>
<simplesect>
<title>Future</title>
<para>
The <classname>parallel\Future</classname> is used to access the return value from the task, and exposes an API for cancellation of the task.
</para>
</simplesect>
<simplesect>
<title>Channel</title>
<para>
A task may be scheduled with arguments, use lexical scope variables (by-value), and return a value (via a <classname>parallel\Future</classname>), but these only allow uni-directional communication:
They allow the programmer to send data into and retrieve data from a task, but do not allow bi-directional communication between tasks.
The <classname>parallel\Channel</classname> API allows bi-directional communication between tasks, a <classname>parallel\Channel</classname> is a socket-like link between tasks that the programmer can use to send and receive data.
</para>
</simplesect>
<simplesect>
<title>Events</title>
<para>
The <classname>parallel\Events</classname> API implements a native feel (<classname>Traversable</classname>) event loop, and <methodname>parallel\Events::poll</methodname> method.
It allows the programmer to work with sets of channels and or futures.
The programmer simply adds channels and futures to the event loop, optionally setting the input for writes with <methodname>parallel\Events::setInput</methodname>,
and enters into a foreach: parallel will read from and write to objects as they become available yielding <classname>parallel\Events\Event</classname> objects
describing the operations that have occurred.
</para>
</simplesect>
<simplesect role="seealso">
&reftitle.seealso;
<simplelist>
<member><xref linkend="philosophy.parallel" /></member>
</simplelist>
</simplesect>
</preface>
&reference.parallel.setup;
&reference.parallel.philosophy;
&reference.parallel.functional;
&reference.parallel.parallel.runtime;
&reference.parallel.parallel.future;
&reference.parallel.parallel.channel;
&reference.parallel.parallel.events;
&reference.parallel.parallel.events.input;
&reference.parallel.parallel.events.event;
&reference.parallel.parallel.events.event.type;
&reference.parallel.parallel.sync;
<!--&reference.parallel.examples;-->
</book>
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