Task Scheduling

To track tasks, we have to revisit how setTimeout() is monkey patched to modify the way Zone’s are tracked.

要跟踪任务，我们必须看下 setTimeout() 的猴子补丁如何修改被跟踪的 zone。

  1. // 保存setTimeout的原始引用
  2. let originalSetTimeout = window.setTimeout;
  3. // 使用在 zone 中包含回调的函数覆盖API。
  4. window.setTimeout = function(callback, delay) {
  5.   // 对当前 zone 使用scheduleTask API。
  6.   Zone.current.scheduleMacroTask(
  7.     // 调试信息
  8.     'setTimeout',
  9.     // 回调需要在当前 zone 执行。
  10.     callback,
  11.     // 可选数据，如任务是否重复。
  12.     null,
  13.     // 默认计划行为
  14.     (task) => {
  15.       return originalSetTimeout(
  16.         // Use the task invoke method, so that the task can
  17.         // call callback in the correct zone.
  18.         task.invoke,
  19.         // original delay information
  20.         delay
  21.       );
  22.     });
  23. }

使用示例：

  1. // Create a logging zone
  2. let logZone = Zone.current.fork({
  3.   onScheduleTask: function(parentZoneDelegate, currentZone,
  4.                            targetZone, task) {
  5.     // Print when async tasks are scheduled
  6.     console.log('Schedule', task.source);
  7.     return parentZoneDelegate.scheduleTask(targetZone, task);
  8.   },
  9.   onInvokeTask: function(parentZoneDelegate, currentZone,
  10.                          targetZone, task, applyThis, applyArgs) {
  11.     // Print when async tasks are invoked
  12.     console.log('Invoke', task.source);
  13.     return parentZoneDelegate.invokeTask(
  14.              targetZone, applyThis, applyArgs);
  15.   }
  16. });
  17. console.log('start');
  18. logZone.run(() => {
  19.   setTimeout(() => null, 0);
  20. });
  21. console.log('end');

输出结果

  1. start
  2. Schedule setTimeout
  3. end
  4. Invoke setTimeout

关键点：

  • All APIs which schedule tasks use Zone.prototype.scheduleTask() instead of Zone.prototype.wrap().
  • Tasks use Zone.prototype.runGuarded() for callback execution, hence they handle all of the errors.
  • Tasks are intercepted using invokeTask() whereas zones are intercepted using invoke().