fix: Allow calling clearTimeout from within the setTimeout callback

Closes #302

Author: mhevery

lib/browser/browser.ts

@@ -86,7 +86,7 @@ function patchTimer(
   var clearNative = patchMethod(window, cancelName, (delegate: Function) => function(self: any, args: any[]) {
     var task: Task = args[0];
     if (task && typeof task.type == 'string') {
-      if (task.cancelFn) {
+      if (task.cancelFn && task.data.isPeriodic || task.runCount == 0) {
         // Do not cancel already canceled functions
         task.zone.cancelTask(task);
       }

lib/zone.ts

@@ -462,6 +462,11 @@ interface Task {
    * at the time of Task creation.
    */
   zone: Zone;
+
+  /**
+   * Number of times the task has been executed, or -1 if canceled.
+   */
+  runCount: number;
 }
 
 interface MicroTask extends Task {
@@ -565,6 +570,7 @@ var Zone: ZoneType = (function(global) {
 
 
     runTask(task: Task, applyThis?: any, applyArgs?: any) {
+      task.runCount++;
       if (task.zone != this)
         throw new Error('A task can only be run in the zone which created it! (Creation: ' +
             task.zone.name + '; Execution: ' + this.name + ')');
@@ -612,6 +618,7 @@ var Zone: ZoneType = (function(global) {
 
     cancelTask(task: Task): any {
       var value = this._zoneDelegate.cancelTask(this, task);
+      task.runCount = -1;
       task.cancelFn = null;
       return value;
     }
@@ -791,6 +798,7 @@ var Zone: ZoneType = (function(global) {
     public scheduleFn: (task: Task) => void;
     public cancelFn: (task: Task) => void;
     public zone: Zone;
+    public runCount: number = 0;
 
     constructor(type: TaskType, zone: Zone, source: string, callback: Function, options: TaskData,
                 scheduleFn: (task: Task) => void, cancelFn:(task: Task) => void)

test/browser/setTimeout.spec.ts

@@ -52,6 +52,13 @@ describe('setTimeout', function () {
     });
   });
 
+  it('should allow cancelation of fns while the task is being executed', function (done) {var spy = jasmine.createSpy('spy');
+    var cancelId = setTimeout(() => {
+      clearTimeout(cancelId);
+      done();
+    }, 0);
+  });
+
   it('should pass invalid values through', function () {
     clearTimeout(null);
     clearTimeout(<any>{});