chrome/browser/resources/local_ntp/local_ntp_util.js

   1 // Copyright 2014 The Chromium Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4
   5
   6 /**
   7  * @fileoverview Utilities for local_ntp.js.
   8  */
   9
  10
  11 /**
  12  * A counter with a callback that gets executed on the 1-to-0 transition.
  13  *
  14  * @param {function()} callback The callback to be executed.
  15  * @constructor
  16  */
  17 function Barrier(callback) {
  18   /** @private {function()} */
  19   this.callback_ = callback;
  20
  21   /** @private {number} */
  22   this.count_ = 0;
  23
  24   /** @private {boolean} */
  25   this.isCancelled_ = false;
  26 }
  27
  28
  29 /**
  30  * Increments count of the Barrier.
  31  */
  32 Barrier.prototype.add = function() {
  33   ++this.count_;
  34 };
  35
  36
  37 /**
  38  * Decrements count of the Barrier, and executes callback on 1-to-0 transition.
  39  */
  40 Barrier.prototype.remove = function() {
  41   if (this.count_ === 0)  // Guards against underflow.
  42     return;
  43   --this.count_;
  44   if (!this.isCancelled_ && this.count_ === 0)
  45     this.callback_();
  46 };
  47
  48
  49 /**
  50  * Deactivates the Barrier; the callback will never be executed.
  51  */
  52 Barrier.prototype.cancel = function() {
  53   this.isCancelled_ = true;
  54 };