php concurrency with pcntl_fork

pcntl_fork.php

$concurrency = 5;
if ($concurrency > 1)
{
    print("Starting {$concurrency} workers via pcntl_fork\n");
    $childPids = array();
    $isMain = true;
    foreach (range(1, $concurrency) as $i) {
        $pid = pcntl_fork();
        if ($pid === -1) throw new Exception("Forking failed.");
        if ($pid === 0)
        {
            // we are the child
            $isMain = false;
            print("New fork started [{$i}]...\n");
            break;
        }
        else
        {
            // $pid is forked child pid
            $childPids[] = $pid;
        }
    }
    if ($isMain)
    {
        foreach ($childPids as $pid)
        {
            pcntl_waitpid($pid, $status);
        }
        print("All kids exited.\n");
        exit(0);
    }
}

// do per-child stuff here

this works great except for if you intend to keep n workers running; it doesn't have a facility to act as a supervisor process or detect signals, etc.