Waitgroups in PHP

Our example demonstrates how to wait for multiple tasks to finish using PHP’s concurrent programming features. We’ll use the parallel extension, which provides a way to run code concurrently in PHP.

First, let’s define our worker function:

function worker($id) {
    echo "Worker $id starting\n";
    sleep(1); // Simulate an expensive task
    echo "Worker $id done\n";
}

Now, let’s set up our main function to run multiple workers concurrently:

function main() {
    $pool = new \parallel\Runtime();
    $futures = [];

    // Launch several tasks and store their futures
    for ($i = 1; $i <= 5; $i++) {
        $futures[] = $pool->run('worker', [$i]);
    }

    // Wait for all tasks to complete
    foreach ($futures as $future) {
        $future->value();
    }
}

main();

In this example:

1. We create a parallel\Runtime object, which manages the execution of concurrent tasks.

2. We launch several tasks using $pool->run(), which returns a Future object for each task.

3. We store these Future objects in an array.

4. Finally, we iterate over the Future objects and call $future->value(), which blocks until the task completes.

To run this program:

$ php waitgroups.php
Worker 1 starting
Worker 2 starting
Worker 3 starting
Worker 4 starting
Worker 5 starting
Worker 1 done
Worker 2 done
Worker 3 done
Worker 4 done
Worker 5 done

The order of workers starting up and finishing is likely to be different for each invocation.

Note that this approach using the parallel extension is relatively new in PHP and requires PHP 7.2+ with the parallel extension installed. For older versions of PHP or environments without this extension, you might need to use other concurrency techniques like multi-processing with pcntl_fork() or job queues.

Also, unlike the original example, PHP’s concurrency model doesn’t have a direct equivalent to WaitGroups. Instead, we use the Future objects returned by $pool->run() to wait for task completion.

For more advanced use cases, consider using a full-fledged job queue system like Gearman or RabbitMQ, which can provide more robust error handling and task management capabilities.