Parallel processing component for Amp.

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v2.0.0-beta.4 2022-11-07 22:50 UTC


AMPHP is a collection of event-driven libraries for PHP designed with fibers and concurrency in mind. amphp/parallel provides true parallel processing for PHP using multiple processes, without blocking and no extensions required.

To be as flexible as possible, this library comes with a collection of non-blocking concurrency tools that can be used independently as needed, as well as an "opinionated" worker API that allows you to assign units of work to a pool of worker processes.

Latest Release MIT License


This package can be installed as a Composer dependency.

composer require amphp/parallel


The basic usage of this library is to submit blocking tasks to be executed by a worker pool in order to avoid blocking the main event loop.


require __DIR__ . '/../vendor/autoload.php';

use Amp\Future;
use Amp\Parallel\Worker;
use function Amp\async;

$urls = [

$executions = [];
foreach ($urls as $url) {
    // FetchTask is just an example, you'll have to implement
    // the Task interface for your task.
    $executions[$url] = Worker\submit(new FetchTask, $url);

// Each submission returns an Execution instance to allow two-way
// communication with a task. Here we're only interested in the
// task result, so we use the Future from Execution::getResult()
$responses = Future\await(array_map(
    fn (Worker\Execution $e => $e->getResult(),

foreach ($responses as $url => $response) {
    \printf("Read %d bytes from %s\n", \strlen($response), $url);

FetchTask is just used as an example for a blocking function here. If you just want to fetch multiple HTTP resources concurrently, it's better to use amphp/http-client, our non-blocking HTTP client.

Note The functions you call must be predefined or autoloadable by Composer, so they also exist in the worker processes.


Worker provides a simple interface for executing PHP code in parallel in a separate PHP process. Classes implementing Task are used to define the code to be run in parallel.


The Task interface has a single run() method that gets invoked in the worker to dispatch the work that needs to be done. The run() method can be written using blocking code since the code is executed in a separate process.

Task instances are serialize'd in the main process and unserialize'd in the worker. That means that all data that is passed between the main process and a worker needs to be serializable.

Worker Pools

The easiest way to use workers is through a worker pool. Worker pools can be used to submit tasks in the same way as a worker, but rather than using a single worker process, the pool uses multiple workers to execute tasks. This allows multiple tasks to be executed simultaneously.

The WorkerPool interface extends Worker, adding methods to get information about the pool or pull a single Worker instance out of the pool. A pool uses multiple Worker instances to execute Task instances.

If a set of tasks should be run within a single worker, use the WorkerPool::getWorker() method to pull a single worker from the pool. The worker is automatically returned to the pool when the instance returned is destroyed.

Global Worker Pool

A global worker pool is available and can be set using the function Amp\Parallel\Worker\workerPool(?WorkerPool $pool = null). Passing an instance of WorkerPool will set the global pool to the given instance. Invoking the function without an instance will return the current global instance.

Child Processes

The ProcessContext class simplifies writing and running PHP in parallel. A script written to be run in parallel must return a callable that will be run in a child process. The callable receives a single argument – an instance of Channel that can be used to send data between the parent and child processes. Any serializable data can be sent across this channel. The Context object, which extends the Channel interface, is the other end of the communication channel.

In the example below, a child process is used to call a blocking function (file_get_contents() is only an example of a blocking function, use http-client for non-blocking HTTP requests). The result of that function is then sent back to the parent using the Channel object. The return value of the child process callable is available using the Context::join() method.

Child Process

# child.php

use Amp\Sync\Channel;

return function (Channel $channel): mixed {
    $url = $channel->receive();

    $data = file_get_contents($url); // Example blocking function


    return 'Any serializable data';

Parent Process

# parent.php

use Amp\Parallel\Context\ProcessContext;

// Creates and starts a child process context using ProcessContext
$context = ProcessContext::start(__DIR__ . '/child.php');

$url = '';

$requestData = $context->receive();
printf("Received %d bytes from %s\n", \strlen($requestData), $url);

$returnValue = $context->join();
printf("Child processes exited with '%s'\n", $returnValue);

Child processes are also great for CPU-intensive operations such as image manipulation or for running daemons that perform periodic tasks based on input from the parent.

Context creation

An execution context can be created using the function Amp\Parallel\Context\startContext(), which uses the global ContextFactory. The global factory is an instance of DefaultContextFactory by default, but this instance can be overridden using the function Amp\Parallel\Context\contextFactory().

Context factories are used by worker pools to create the context which executes tasks. Providing a custom ContextFactory to a worker pool allows custom bootstrapping or other behavior within pool workers.

An execution context can be created by a ContextFactory. The worker pool uses context factories to create workers.

A global worker pool is available and can be set using the function Amp\Parallel\Worker\workerPool(?WorkerPool $pool = null). Passing an instance of WorkerPool will set the global pool to the given instance. Invoking the function without an instance will return the current global instance.


amphp/parallel follows the semver semantic versioning specification like all other amphp packages.


If you discover any security related issues, please use the private security issue reporter instead of using the public issue tracker.


The MIT License (MIT). Please see LICENSE for more information.