AngularJS で Semaphore してみたい

app.js

'use strict';

angular.module('myApp', [
    'ngResource',
    'ngSemaphore'
]).config(function ($provide) {
    $provide.value('SemaphoreConfig', {
        parallels: 5
    });
}).controller(
  'MainCtrl', function ($scope, $resouce, Semaphore) {

    $scope.getApiData = function (url) {
      Semaphore.down(function (sem) { // Semaphore が down( ) できなければ Queue に入る
          $resource(url).get( ).then(function (response) {
              // ...
              sem.up( ); // 最後に Semaphore を up( ) する
          });
      });
    };
});

semaphore.js

'use strict';

angular.module('myApp').factory(
  'Semaphore', function ($q, SemaphoreConfig) {

    var klass = {
      parallels: SemaphoreConfig.parallels || 5,
      queues: [ ]
    };

    klass.remain = klass.parallels;

    klass.down = function (callback, context) {
      var deferred = $q.defer( );
      var semaphore = new SemaphoreInstance(deferred);

      if (klass.remain == 0) {
        klass.queues.push({
            callback: callback,
            context:  context
        });
      } else {
        --klass.remain;
        callback.call(context, semaphore);
      }
    };

    var onSemaphoreUp = function ( ) {
      var queue = klass.queues.shift( );

      if (queue) {
        klass.down(queue.callback, queue.context);
      };
    };

    var SemaphoreInstance = function (deferred) {
      this.deferred = deferred;
      this.deferred.promise.then(onSemaphoreUp);
    };

    SemaphoreInstance.prototype.up = function ( ) {
      if (klass.remain >= klass.parallels) {
        this.deferred.reject( );
      } else {
        ++klass.remain;
        this.deferred.resolve( );
      }
    };

    return klass;
});