declare(ticks=1);

pcntl_signal(SIGCHLD, "sig_handler");

function sig_handler($signo)

{

    switch ($signo) {

        case SIGCHLD:

            $status = 0;

            $child_id = pcntl_wait($status);

            echo sprintf("child exit id: {$child_id} \n");

            exit(0);

            break;

        default:

            echo 'uncaugh signal !';

    }

}

$pid = pcntl_fork();

if($pid>0)

{

    echo sprintf("fork child id: {$pid} \n");

    while(1){

        sleep(1);

    }

}else{

    echo "child exit \n";

}