fix(scheduler): prevent unwanted clearInterval (#3226)

* test(scheduler): add interval recycling tests

* fix(scheduler): prevent unwanted clearInterval

In AsyncAction, this.pending was assigned before the call to
recycleAsyncId. That prevented the interval from being re-used resulting
in the interval being cleared and re-created for each notification.

Closes #3042

spec/schedulers/AsapScheduler-spec.ts

@@ -40,6 +40,59 @@ describe('Scheduler.asap', () => {
     sandbox.restore();
   });
 
+  it('should reuse the interval for recursively scheduled actions with the same delay', () => {
+    const sandbox = sinon.sandbox.create();
+    const fakeTimer = sandbox.useFakeTimers();
+    // callThrough is missing from the declarations installed by the typings tool in stable
+    const stubSetInterval = (<any> sinon.stub(global, 'setInterval')).callThrough();
+    function dispatch(state: any): void {
+      state.index += 1;
+      if (state.index < 3) {
+        (<any> this).schedule(state, state.period);
+      }
+    }
+    const period = 50;
+    const state = { index: 0, period };
+    asap.schedule(dispatch, period, state);
+    expect(state).to.have.property('index', 0);
+    expect(stubSetInterval).to.have.property('callCount', 1);
+    fakeTimer.tick(period);
+    expect(state).to.have.property('index', 1);
+    expect(stubSetInterval).to.have.property('callCount', 1);
+    fakeTimer.tick(period);
+    expect(state).to.have.property('index', 2);
+    expect(stubSetInterval).to.have.property('callCount', 1);
+    stubSetInterval.restore();
+    sandbox.restore();
+  });
+
+  it('should not reuse the interval for recursively scheduled actions with a different delay', () => {
+    const sandbox = sinon.sandbox.create();
+    const fakeTimer = sandbox.useFakeTimers();
+    // callThrough is missing from the declarations installed by the typings tool in stable
+    const stubSetInterval = (<any> sinon.stub(global, 'setInterval')).callThrough();
+    function dispatch(state: any): void {
+      state.index += 1;
+      state.period -= 1;
+      if (state.index < 3) {
+        (<any> this).schedule(state, state.period);
+      }
+    }
+    const period = 50;
+    const state = { index: 0, period };
+    asap.schedule(dispatch, period, state);
+    expect(state).to.have.property('index', 0);
+    expect(stubSetInterval).to.have.property('callCount', 1);
+    fakeTimer.tick(period);
+    expect(state).to.have.property('index', 1);
+    expect(stubSetInterval).to.have.property('callCount', 2);
+    fakeTimer.tick(period);
+    expect(state).to.have.property('index', 2);
+    expect(stubSetInterval).to.have.property('callCount', 3);
+    stubSetInterval.restore();
+    sandbox.restore();
+  });
+
   it('should schedule an action to happen later', (done: MochaDone) => {
     let actionHappened = false;
     asap.schedule(() => {

src/internal/scheduler/AsyncAction.ts

@@ -29,10 +29,6 @@ export class AsyncAction<T> extends Action<T> {
     // Always replace the current state with the new state.
     this.state = state;
 
-    // Set the pending flag indicating that this action has been scheduled, or
-    // has recursively rescheduled itself.
-    this.pending = true;
-
     const id = this.id;
     const scheduler = this.scheduler;
 
@@ -61,6 +57,10 @@ export class AsyncAction<T> extends Action<T> {
       this.id = this.recycleAsyncId(scheduler, id, delay);
     }
 
+    // Set the pending flag indicating that this action has been scheduled, or
+    // has recursively rescheduled itself.
+    this.pending = true;
+
     this.delay = delay;
     // If this action has already an async Id, don't request a new one.
     this.id = this.id || this.requestAsyncId(scheduler, this.id, delay);