parallel

A succinct parallel concurrency API for PHP 7:

final class parallel\Runtime {
	/*
	* Shall construct a new Runtime
	* @param string bootstrap (generally an autoloader)
	* @param array  ini configuration
	* @throws \parallel\Exception if arguments are invalid
	* @throws \parallel\Exception if bootstrapping failed
	* @throws \parallel\Exception the thread could not be created
	*/
	public function __construct(string $bootstrap, array $configuration);
	/**
	* Shall construct a new Runtime
	* @param string bootstrap (generally an autoloader)
	* @throws \parallel\Exception if arguments are invalid
	* @throws \parallel\Exception if bootstrapping failed
	* @throws \parallel\Exception if the thread could not be created	
	**/
	public function __construct(string $bootstrap);
	/**
	* Shall construct a new Runtime
	* @throws \parallel\Exception if arguments are invalid
	* @throws \parallel\Exception if the thread could not be created
	* @param array ini configuration
	**/
	public function __construct(array $configuration);

	/*
	* Shall schedule a Closure for execution passing optional arguments
	* @param Closure handler
	* @param array argv
	* @throws \parallel\Exception if \parallel\Runtime was closed
	* @throws \parallel\Exception if \parallel\Runtime is in unusable state
	* @throws \parallel\Exception if Closure contains illegal instructions
	* @throws \parallel\Exception if return from Closure is ignored
	* Note: A Future shall only be returned if $handler contains a return statement
	*	Should the caller ignore the return statement in $handler, an exception
	*	shall be thrown
	*/
	public function run(Closure $handler, array $argv = []) : ?\parallel\Future;
	
	/*
	* Shall request the Runtime shutdown
	* Note: Closures scheduled for execution will be executed
	* @throws \parallel\Exception if \parallel\Runtime was already closed
	*/
	public function close() : void;

	/*
	* Shall kill the Runtime
	* Note: Closures scheduled for execution will not be executed,
	*	currently running Closure will be interrupted.
	* Note: Cannot interrupt internal function calls in progress
	* @throws \parallel\Exception if \parallel\Runtime was already closed
	*/
	public function kill() : void;
}

final class parallel\Future {
	/*
	* Shall wait until the value is resolved
	* @throws \parallel\Exception if Closure was killed
	* @throws \parallel\Exception if \parallel\Runtime was closed before execution
	* @throws \parallel\Exception if \parallel\Runtime was killed during execution
	* @throws \parallel\Exception if Closure suffered a fatal error or exception
	*/
	public function value() : mixed;

	/*
	* Shall wait until the value is resolved or the timeout is reached
	* @param non-negative timeout in microseconds
	* @throws \parallel\Exception if Closure was killed
	* @throws \parallel\Exception if \parallel\Runtime was closed before execution
	* @throws \parallel\Exception if \parallel\Runtime was killed during execution
	* @throws \parallel\Exception if Closure suffered a fatal error or exception
	* @throws \parallel\Exception if timeout is negative
	* @throws \parallel\TimeoutException if timeout is reached
	*/
	public function value(int $timeout) : mixed;

	/*
	* Shall indicate if the Future value is resolved
	* @returns bool
	*/
	public function done() : bool;

	/*
	* Shall perform a select on the Future objects in $resolving,
	*	returning upon the first successful resolve
	* @param array $resolving array of Future objects
	* @param array $resolved  shall be filled with resolved Future objects
	* @param array $errored   shall be filled with Future objects that errored
	* @return number of resolved and errored Future objects
	* @throws \parallel\Exception if the arguments are invalid
	*/
	public static function select(array &$resolving, array &$resolved, array &$errored) : int;

	/*
	* Shall perform a select on the Future objects in $resolving, 
	*	returning upon the first successful resolve, 
	*	with the given timeout in microseconds
	* @param array $resolving array of Future objects
	* @param array $resolved  shall be filled with resolved Future objects
	* @param array $errored   shall be filled with Future objects that errored
	* @param array $timedout  shall be filled with Future objects that timedout
	* @param int   $timeout   timeout in microseconds
	* @return number of resolved, errored, and timedout Future objects
	* @throws \parallel\Exception if the arguments are invalid
	*/
	public static function select(array &$resolving, array &$resolved, array &$errored, array &$timedout, int $timeout) : int;
}

Implementation

In PHP there was only one kind of parallel concurrency extension API, the kind that pthreads and pht try to implement:

• They are hugely complicated
• They are error prone
• They are difficult to understand
• They are difficult to deploy
• They are difficult to maintain

parallel takes a totally different approach to these two by providing only a very small, easy to understand API that exposes the power of parallel concurrency without any of the aforementioned headaches.

By placing some restrictions upon what a Closure intended for parallel execution can do, we remove almost all of the cognitive overhead of using threads, we hide away completely any mutual exclusion and all the things a programmer using threads must think about.

In practice this means Closures intended for parallel execution must not:

• accept or return by reference
• accept or return objects
• execute a limited set of instructions

Instructions prohibited directly in Closures intended for parallel execution are:

• declare (anonymous) function
• declare (anonymous) class
• lexical scope access
• yield

No instructions are prohibited in the files which the Runtime may include.

Requirements

• PHP 7.1+
• ZTS
• <pthread.h>

Configuring the Runtime

The optional bootstrap file passed to the constructor will be included before any code is executed, generally this will be an autoloader.

The configuration array passed to the constructor will configure the Runtime using INI.

The following options may be an array, or comma separated list:

• disable_functions
• disable_classes

The following options will be ignored:

• extension - use dl()
• zend_extension - unsupported

All other options are passed directly to zend verbatim and set as if set by system configuration file.

Hello World

<?php
$runtime = new \parallel\Runtime();

$future = $runtime->run(function(){
	for ($i = 0; $i < 500; $i++)
		echo "*";

	return "easy";
});

for ($i = 0; $i < 500; $i++) {
	echo ".";
}

printf("\nUsing \\parallel\\Runtime is %s\n", $future->value());

This may output something like (output abbreviated):

.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*
Using \parallel\Runtime is easy