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3 years ago
<?php

declare(strict_types = 1);

/**
  * Helper method to execute a task
  */
function execute_task(int $task_id): void
{
    echo 'Starting task: ' . $task_id . PHP_EOL;

    // Simulate doing actual work with sleep()
    $execution_time = rand(5, 10);
    sleep($execution_time);

    echo "Completed task: ${task_id}. Took ${execution_time} seconds.\n";
}

/**
  * Builds a list of tasks
  */
function generator(): Generator
{
    $item_count = 50;
    for ($i = 1; $i <= $item_count; $i++) {
        yield $i;
    }
}

/**
  * Starts the work
  */
function launch(): void
{
    $processCount = 0;
    $status       = null;
    echo 'Running as pid: ' . getmypid() . PHP_EOL;

    $taskList = generator();
    do {
        echo 'Still tasks to do' . PHP_EOL;

        if ($processCount >= 5) {
            echo 'Waiting, currently running: ' . $processCount . PHP_EOL;
            pcntl_wait($status);
            $processCount--;
            continue;
        }

        echo 'Tasks running: ' . $processCount . PHP_EOL;
        $task = $taskList->current();
        $taskList->next();
        $processCount++;

        $pid = pcntl_fork();

        if ($pid === -1) {
            exit('Error forking...' . PHP_EOL);
        }

        if ($pid === 0) {
            $processList[] = getmypid();
            echo 'Running task as pid: ' . getmypid() . PHP_EOL;
            execute_task($task);
            exit();
        }
    } while ($taskList->valid());

    $waitForChildrenToFinish = true;
    while ($waitForChildrenToFinish) {
        // This while loop holds the parent process until all the child threads
        // are complete - at which point the script continues to execute.
        if (pcntl_waitpid(0, $status) === -1) {
            echo 'parallel execution is complete' . PHP_EOL;
            $waitForChildrenToFinish = false;
        }
    }

    // Code to run after all tasks are processed
}

launch();
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