javascript - 尝试同步AJAX请求

我一直在为我编写的Facebook游戏开发新功能。该游戏允许玩家在欧洲各城市之间旅行并交付商品以获取利润。我要添加的此功能为游戏添加了寻路AI：它允许玩家选择要前往的城市，然后游戏会自动将其火车沿轨道从其起始城市移动到目标城市。我正在使用AJAX和setTimeout（）从后端获取数据，并使火车沿着连接城市的轨道运动。请参考代码（希望）能更好地理解我的意图。

问题是setTimeout（）经常被调用。我放置了一个名为statusFinalDest的全局变量，该变量可能包含两个值：ENROUTE和ARRIVED。当火车为ENROUTE时，JS火车运动功能使用setTimeout调用自身，直到后端返回ARRIVED的statusFinalDest，此时火车运动超时循环（据说）终止。但是，与其每回合调用一次后端进程一次都不调用myEventMoveTrainManual（），而是要频繁地调用它，好像它无法识别statusFinalDest的已更改状态一样。我试图在代码中添加更多的限制结构来结束这种过度的行为，但它们似乎没有用。

以下是相关的FBJS（Facebook JS）代码：

function myEventMoveTrainManual(evt) {
      if(mutexMoveTrainManual == 'CONTINUE') {
        //mutexMoveTrainManual = 'LOCKED';
        var ajax = new Ajax();
        var param = {};
        if(evt) {
          var cityId = evt.target.getParentNode().getId();
          var param = { "city_id": cityId };
        }
        ajax.responseType = Ajax.JSON;
        ajax.ondone = function(data) {
          statusFinalDest = data.status_final_dest;
          if(data.code != 'ERROR_FINAL_DEST') {

            // Draw train at new location
            trackAjax = new Ajax();
            trackAjax.responseType = Ajax.JSON;
            trackAjax.ondone = function(trackData) {
              var trains = [];
              trains[0] = trackData.train;
              removeTrain(trains);
              drawTrack(trackData.y1, trackData.x1, trackData.y2, trackData.x2, '#FF0', trains);

              if(data.code == 'UNLOAD_CARGO') {
                unloadCargo();
              } else if (data.code == 'MOVE_TRAIN_AUTO' || data.code == 'TURN_END') {
                moveTrainAuto();
              } else {
                /* handle error */
              }
              mutexMoveTrainManual = 'CONTINUE';
            }
            trackAjax.post(baseURL + '/turn/get-track-data');
          }
        }
        ajax.post(baseURL + '/turn/move-train-set-destination', param);
      }

      // If we still haven't ARRIVED at our final destination, we are ENROUTE so continue
      // moving the train until final destination is reached
      // statusFinalDest is a global var
      if(statusFinalDest == 'ENROUTE') {
        setTimeout(myEventMoveTrainManual, 1000);
      }
}

这是后端PHP代码：

  public function moveTrainSetDestinationAction() {
    require_once 'Train.php';
    $trainModel = new Train();

    $userNamespace = new Zend_Session_Namespace('User');
    $gameNamespace = new Zend_Session_Namespace('Game');

    $this->_helper->layout()->disableLayout();
    $this->_helper->viewRenderer->setNoRender();

    $trainRow = $trainModel->getTrain($userNamespace->gamePlayerId);
    $statusFinalDest = $trainRow['status_final_dest'];
    if($statusFinalDest == 'ARRIVED') {
      $originCityId = $trainRow['dest_city_id'];
      $destCityId = $this->getRequest()->getPost('city_id');
      if(empty($destCityId)) {
        // If we arrived at final dest but user supplied no city then this method got called
        // incorrectly so return an error
        echo Zend_Json::encode(array('code' => 'ERROR_FINAL_DEST', 'status_final_dest' => $statusFinalDest));
        exit;
      }

      $gameNamespace->itinerary = $this->_helper->getTrainItinerary($originCityId, $destCityId);
      array_shift($gameNamespace->itinerary); //shift-off the current train city location
      $trainModel->setStatusFinalDest('ENROUTE', $userNamespace->gamePlayerId);
      $statusFinalDest = 'ENROUTE';
    }
    $cityId = $trainRow['dest_city_id'];
    if($trainRow['status'] == 'ARRIVED') {
      if(count($gameNamespace->itinerary) > 0) {
        $cityId = array_shift($gameNamespace->itinerary);
      }
    }
    $trainRow = $this->_helper->moveTrain($cityId);
    if(count($trainRow) > 0) {
      if($trainRow['status'] == 'ARRIVED') {
        // If there are no further cities on the itinerary, we have arrived at our final destination
        if(count($gameNamespace->itinerary) == 0) {
          $trainModel->setStatusFinalDest('ARRIVED', $userNamespace->gamePlayerId);
          $statusFinalDest = 'ARRIVED';
        }
        echo Zend_Json::encode(array('code' => 'UNLOAD_CARGO', 'status_final_dest' => $statusFinalDest));
        exit;
        // Pass id for last city user selected so we can return user to previous map scroll postion
      } else if($trainRow['track_units_remaining'] > 0) {
        echo Zend_Json::encode(array('code' => 'MOVE_TRAIN_AUTO', 'status_final_dest' => $statusFinalDest));
        exit;
      } else { /* Turn has ended */
        echo Zend_Json::encode(array('code' => 'TURN_END', 'status_final_dest' => $statusFinalDest));
        exit;
      }
    }
    echo Zend_Json::encode(array('code' => 'MOVE_TRAIN_AUTO_ERROR'));
  }

最佳答案

如果从事件处理程序中调用函数myEventMoveTrainManual，则每次事件发生时，您都将运行一个新计时器。

一个应该有用的简单技巧是在启动新计时器之前先杀死计时器：

var timerId;

//...
clearTimeout(timerId);
timerId = setTimeout(myEventMoveTrainManual, 1000);
//...

但是我认为您真正想做的是调用一个不同的函数，该函数检查计时器循环是否已在运行，如果没有，则调用myEventMoveTrainManual。