README

Fork is a library for running jobs concurrently in PHP. It works by forking the main process into separate tasks using PHP's pcntl and sockets extensions. So, it should go without saying that this library will not work on Windows.

There is an existing library for forking processes, spatie/fork. This library on its surface is very similar, but internally it's quite a bit different. Unlike spatie/fork, mensbeam/fork does not return an array of returned values from all tasks after all of them have finished. Instead, it uses callbacks to handle output as each task completes. This design prevents potential memory exhaustion when running a large number of tasks, as we encountered when using spatie/fork. Handling output immediately as tasks finish is more scalable and efficient.

Requirements

Installation

Install using Composer:

composer require mensbeam/fork

Usage

Here is a simple example. Fork->run() can accept an array or an \Iterator of callables to run concurrently and will execute them. This means it can also accept a generator to continuously run tasks concurrently.

use MensBeam\Fork;

function gen(): \Generator {
    foreach (range(1, 5) as $n) {
        yield function () use ($n) {
            $delay = rand(1, 5);
            sleep($delay);
            return [ $n, $delay ];
        };
    }
}

(new Fork())->after(function(array $output) {
    echo "{$output['data'][0]}: {$output['data'][1]}\n";
})->run(gen());

Example output:

4: 2
3: 2
2: 3
5: 3
1: 5

Callbacks

You can use before() and after() to register callbacks to run before or after each task. You can register different callbacks for the parent and child processes.

Concurrency

You can limit how many tasks run concurrently using concurrent().

use MensBeam\Fork;

(new Fork())->concurrent(2)->run([
    fn() => sleep(1),
    fn() => sleep(1),
    fn() => sleep(1)
]);

Timeouts

You can set a timeout (in seconds) for each child process:

use MensBeam\Fork;

(new Fork())->timeout(5)->run([
    fn() => sleep(10), // This will timeout
    fn() => sleep(2)
]);

When a task times out, a TimeoutException is thrown inside the child process, and a ThrowableContext object is sent back to the parent.

Stopping tasks

You can stop all currently running and queued tasks from within an after() callback:

use MensBeam\Fork;

$f = new Fork();
$f->after(function(array $output) use ($f) {
    if ($output['data'] === 'stop') {
        $f->stop();
    }
})->run([
    fn() => 'continue',
    fn() => 'stop',
    fn() => 'never runs'
]);

ThrowableContext

When a task throws an exception or error in a child process, a ThrowableContext instance is returned to the parent.

What it includes

Error code
File and line where the throwable was thrown
Message
Class type
Optional stack trace (enabled via Fork::$tracesInThrowableContexts)
Any previous throwable chain

Example

use MensBeam\Fork;

(new Fork())->after(function(array $output) {
    if ($output['data'] instanceof MensBeam\Fork\ThrowableContext) {
        echo "Child failed with: " . $output['data']->getMessage() . "\n";
    } else {
        echo "Child succeeded with: " . $output['data'] . "\n";
    }
})->run([
    fn() => throw new \RuntimeException("Something went wrong!"),
    fn() => "All good"
]);

Handling traces

You can enable including stack traces in ThrowableContext objects:

use MensBeam\Fork;
Fork::$tracesInThrowableContexts = true;

Keep in mind there are some minor limitations, however. Anything that can't be serialized such as Generators, Closures, etc. are all sanitized to strings denoting what they were before being replaced.

Throwing exceptions inside the fork

By default, exceptions inside child processes are caught and sent as ThrowableContext objects. If you'd like them to be thrown, crash the child process, and therefore be printed (for debugging or crash reporting), set:

use MensBeam\Fork;
Fork::$throwInFork = true;

(new Fork())->after(function(array $output) {
    echo "Ook!\n";
})->run([
    fn() => throw new \RuntimeException('Eek!'))
]);