PHP Forking with child process limit

function runProcessor()
{
    $max_fork = 2;
    $tasks = [
      "test1" => "process1",
      "test2" => "process2",
      "test3" => "process3",
      "test4" => "process4",
      "test5" => "process5",
      "test6" => "process6",
      "test7" => "process7",
      "test8" => "process8",
      "test9" => "process9",
      "test10" => "process10",
    ];
    $pids = array();
    $pid_count = 0;

    foreach ( $tasks as $seq => $task ) {

        $pids[$pid_count] = pcntl_fork();
        switch($pids[$pid_count]) {
            case "0":
                return execute_task($task);
                break;
            case "-1":
                echo "Unable to fork new process\n";
                exit;
                break;
            default:
                $pid_count++;
                while( count( $pids ) >= $max_fork ) {
                    foreach( $pids as $key=>$pid ) {
                        $pid_status = "";
                        if( -1 == pcntl_waitpid( $pid, $pid_status, WNOHANG ) ) {
                            unset($pids[$key]);
                            continue;
                        }
                    }
                    usleep(200000);
                }
                break;
        }
    }

    exit();
}

function execute_task($task_id) {
  echo "Starting task: ${task_id}\n";
  // Simulate doing actual work with sleep().
  $execution_time = rand(5, 10);
  sleep($execution_time);
  echo "Completed task: ${task_id}. Took ${execution_time} seconds.\n";

  exit();
}


runProcessor();