PHP Daemon/worker environment

Question

Problem: I want to implement several php-worker processes who are listening on a MQ-server queue for asynchronous jobs. The problem now is that simply running this processes

Answer 1

Bellow is our working implementation of @chaos answer. Code to handle signals was removed as this script lives usually just few milliseconds.

Also, in code we added 2 functions to save pids between calls: restore_processors_state() and save_processors_state(). We've used redis there, but you can decide to use implementation on files.

We run this script every minute using cron. Cron checks if all processes alive. If not - it re-run them and then dies. If we want to kill existing processes then we simply run this script with argument kill: php script.php kill.

Very handy way of running workers without injecting scripts into init.d.

hget('worker_procs', 'pids');

    if( !$pids )
    {
        $processors = array();
    }
    else
    {
        $processors = json_decode($pids, true);
    }
}

function save_processors_state()
{
    global $processors;

    $redis = Zend_Registry::get('redis');
    $redis->hset('worker_procs', 'pids', json_encode($processors));
}

function spawn_processor() {
    $pid = pcntl_fork();
    if($pid) {
        global $processors;
        $processors[] = $pid;
    } else {
        if(posix_setsid() == -1)
            die("Forked process could not detach from terminal\n");
        fclose(STDIN);
        fclose(STDOUT);
        fclose(STDERR);
        pcntl_exec('/usr/bin/php', array(PROCESSOR_EXECUTABLE));
        die('Failed to fork ' . PROCESSOR_EXECUTABLE . "\n");
    }
}

function spawn_processors() {
    restore_processors_state();

    check_processors();

    save_processors_state();
}

function kill_processors() {
    global $processors;
    foreach($processors as $processor)
        posix_kill($processor, SIGTERM);
    foreach($processors as $processor)
        pcntl_waitpid($processor, $trash);
    unset($processors);
}

function check_processors() {
    global $processors;
    $valid = array();
    foreach($processors as $processor) {
        pcntl_waitpid($processor, $status, WNOHANG);
        if(posix_getsid($processor))
            $valid[] = $processor;
    }
    $processors = $valid;
    if(count($processors) > WANT_PROCESSORS) {
        for($ix = count($processors) - 1; $ix >= WANT_PROCESSORS; $ix--)
            posix_kill($processors[$ix], SIGTERM);
        for($ix = count($processors) - 1; $ix >= WANT_PROCESSORS; $ix--)
            pcntl_waitpid($processors[$ix], $trash);
    }
    elseif(count($processors) < WANT_PROCESSORS) {
        for($ix = count($processors); $ix < WANT_PROCESSORS; $ix++)
            spawn_processor();
    }
}

if( isset($argv) && count($argv) > 1 ) {
    if( $argv[1] == 'kill' ) {
        restore_processors_state();
        kill_processors();
        save_processors_state();

        exit(0);
    }
}

spawn_processors();