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Asynchronous and parallel PHP

This library provides a small and easy wrapper around PHP's PCNTL extension. It allows running of different processes in parallel, with an easy-to-use API.

Installation

You can install the package via composer:

Usage

Event listeners

When creating asynchronous processes, you'll get an instance of ParallelProcess returned. You can add the following event hooks on a process.

Functional API

Instead of using methods on the $pool object, you may also use the async and await helper functions.

Error handling

If an Exception or Error is thrown from within a child process, it can be caught per process by specifying a callback in the ->catch() method.

If there's no error handler added, the error will be thrown in the parent process when calling await() or $pool->wait().

If the child process would unexpectedly stop without throwing an Throwable, the output written to stderr will be wrapped and thrown as Spatie\Async\ParallelError in the parent process.

Catching exceptions by type

By type hinting the catch functions, you can provide multiple error handlers, each for individual types of errors.

Note that as soon as an exception is handled, it won't trigger any other handlers

Working with tasks

Besides using closures, you can also work with a Task. A Task is useful in situations where you need more setup work in the child process. Because a child process is always bootstrapped from nothing, chances are you'll want to initialise eg. the dependency container before executing the task. The Task class makes this easier to do.

Simple tasks

If you want to encapsulate the logic of your task, but don't want to create a full blown Task object, you may also pass an invokable object to the Pool.

Pool configuration

You're free to create as many pools as you want, each pool has its own queue of processes it will handle.

A pool is configurable by the developer:

Synchronous fallback

If the required extensions (pcntl and posix) are not installed in your current PHP runtime, the Pool will automatically fallback to synchronous execution of tasks.

The Pool class has a static method isSupported you can call to check whether your platform is able to run asynchronous processes.

If you're using a Task to run processes, only the run method of those tasks will be called when running in synchronous mode.

Behind the curtains

When using this package, you're probably wondering what's happening underneath the surface.

We're using the symfony/process component to create and manage child processes in PHP. By creating child processes on the fly, we're able to execute PHP scripts in parallel. This parallelism can improve performance significantly when dealing with multiple synchronous tasks, which don't really need to wait for each other. By giving these tasks a separate process to run on, the underlying operating system can take care of running them in parallel.

There's a caveat when dynamically spawning processes: you need to make sure that there won't be too many processes at once, or the application might crash. The Pool class provided by this package takes care of handling as many processes as you want by scheduling and running them when it's possible.

That's the part that async() or $pool->add() does. Now let's look at what await() or $pool->wait() does.

When multiple processes are spawned, each can have a separate time to completion. One process might eg. have to wait for a HTTP call, while the other has to process large amounts of data. Sometimes you also have points in your code which have to wait until the result of a process is returned.

This is why we have to wait at a certain point in time: for all processes on a pool to finish, so we can be sure it's safe to continue without accidentally killing the child processes which aren't done yet.

Waiting for all processes is done by using a while loop, which will wait until all processes are finished. Determining when a process is finished is done by using a listener on the SIGCHLD signal. This signal is emitted when a child process is finished by the OS kernel. As of PHP 7.1, there's much better support for listening and handling signals, making this approach more performant than eg. using process forks or sockets for communication. You can read more about it here.

When a process is finished, its success event is triggered, which you can hook into with the ->then() function. Likewise, when a process fails or times out, the loop will update that process' status and move on. When all processes are finished, the while loop will see that there's nothing more to wait for, and stop. This is the moment your parent process can continue to execute.

Comparison to other libraries

We've written a blog post containing more information about use cases for this package, as well as making comparisons to other asynchronous PHP libraries like ReactPHP and Amp: http://stitcher.io/blog/asynchronous-php.

Testing

Changelog

Please see CHANGELOG for more information what has changed recently.

Contributing

Please see CONTRIBUTING for details.

Security

If you discover any security related issues, please email [email protected] instead of using the issue tracker.

Postcardware

You're free to use this package, but if it makes it to your production environment we highly appreciate you sending us a postcard from your hometown, mentioning which of our package(s) you are using.

Our address is: Spatie, Samberstraat 69D, 2060 Antwerp, Belgium.

We publish all received postcards on our company website.

Credits

• Brent Roose
• All Contributors

Support us

Spatie is a webdesign agency based in Antwerp, Belgium. You'll find an overview of all our open source projects on our website.

Does your business depend on our contributions? Reach out and support us on Patreon. All pledges will be dedicated to allocating workforce on maintenance and new awesome stuff.

License

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