How does PHP handle parallel script execution and communication without queues?

PHP can handle parallel script execution and communication without queues by using the `pcntl_fork()` function to create child processes that can run concurrently. These child processes can communicate with each other using shared memory or other inter-process communication methods. Here is an example code snippet that demonstrates how to use `pcntl_fork()` to achieve parallel script execution:

$children = array();

for ($i = 0; $i < 5; $i++) {
    $pid = pcntl_fork();
    
    if ($pid == -1) {
        die('Could not fork');
    } elseif ($pid) {
        // Parent process
        $children[] = $pid;
    } else {
        // Child process
        echo "Child process $i\n";
        sleep(2);
        exit();
    }
}

// Wait for all child processes to finish
foreach ($children as $pid) {
    pcntl_waitpid($pid, $status);
}