?php
class Task
{
  protected $taskId;
  protected $coroutine;
  protected $sendValue = null;
  protected $beforeFirstYield = true;
  public function __construct($taskId, Generator $coroutine)
  {
    $this->taskId = $taskId;
    $this->coroutine = $coroutine;
  }
  public function getTaskId()
  {
    return $this->taskId;
  }
  public function setSendValue($sendValue)
  {
    $this->sendValue = $sendValue;
  }
  public function run()
  {
    if ($this->beforeFirstYield) {
      $this->beforeFirstYield = false;
      return $this->coroutine->current();
    } else {
      $retval = $this->coroutine->send($this->sendValue);
      $this->sendValue = null;
      return $retval;
    }
  }
  public function isFinished()
  {
    return !$this->coroutine->valid();
  }
}
class Scheduler
{
  protected $maxTaskId = 0;
  protected $taskMap = []; // taskId => task
  protected $taskQueue;
  public function __construct()
  {
    $this->taskQueue = new SplQueue();
  }
  public function newTask(Generator $coroutine)
  {
    $tid = ++$this->maxTaskId;
    $task = new Task($tid, $coroutine);
    $this->taskMap[$tid] = $task;
    $this->schedule($task);
    return $tid;
  }
  public function schedule(Task $task)
  {
    $this->taskQueue->enqueue($task);
  }
  public function run()
  {
    while (!$this->taskQueue->isEmpty()) {
      $task = $this->taskQueue->dequeue();
      $task->run();
      if ($task->isFinished()) {
        unset($this->taskMap[$task->getTaskId()]);
      } else {
        $this->schedule($task);
      }
    }
  }
}
function task1()
{
  for ($i = 1; $i = 10; ++$i) {
    echo "This is task 1 iteration $i.\n";
    sleep(1);
    yield;
  }
}
function task2()
{
  for ($i = 1; $i = 10; ++$i) {
    echo "This is task 2 iteration $i.\n";
    sleep(1);
    yield;
  }
}
$scheduler = new Scheduler;
$scheduler->newTask(task1());
$scheduler->newTask(task2());
$scheduler->run();