angularjs多个控制器公用一个服务问题

factory('DemoService', function() {
  var observerCallbacks = [];

  var notifyObservers = function(){
    angular.forEach(observerCallbacks, function(callback){
      callback();
    });
  };

  var service = {
    shareValue: 'shareValue',
    registerObserverCallback: function(callback){
      observerCallbacks.push(callback);
    },
    setShareValue: function(val) {
      this.shareValue = val;
      notifyObservers();
    }
  };
  return service;
});

Controller：

function FooCtrl($scope, DemoService){
  var updateFoo = function(){
    $scope.foo = DemoService.foo;
  };

  DemoService.registerObserverCallback(updateFoo);

  DemoService.setShareValue('new value');
};