1411501 - Runnable is not executed as expected when TailDispatching, Non-TailDispatching TaskQueue are mix-used.

Status: RESOLVED WORKSFORME

(Core :: Audio/Video: Playback, defect)

Description

[Kilik Kuo [:kikuo] (inactive)]

During the investigation on Bug 1313449,
I posted a patch which invokes |mOnWaitingForKeyEvent->Notify| [1] on a Non-TailDispatching thread (IPC receiver).
And there's also a case which|mOnWaitingForKeyEvent->Notify| is invoked on MFR's TaskQueue [2].


I found sometimes the dispatched runnables are not executed in order as expected.
[2] will be invoked before [1], but the runnable created by [1] is executed earlier than the one created by [2].

So the testing scenario would be exactly like TestTaskQueue.cpp [3] and setting tq2's aSupportsTailDispatch to false.

Is this a bug or it's intentional by the design here [4] ?


[1] https://bugzilla.mozilla.org/attachment.cgi?id=8920054&action=diff#a/dom/media/platforms/agnostic/eme/SamplesWaitingForKey.cpp_sec4
[2] http://searchfox.org/mozilla-central/rev/d30462037ffea383e74c42542c820cf65b2b144e/dom/media/platforms/agnostic/eme/SamplesWaitingForKey.cpp#50
[3] http://searchfox.org/mozilla-central/source/xpcom/tests/gtest/TestTaskQueue.cpp
[4] http://searchfox.org/mozilla-central/rev/d30462037ffea383e74c42542c820cf65b2b144e/xpcom/threads/TaskQueue.cpp#245-246

Comment 1

[JW Wang [:jwwang] [:jw_wang]]

Per offline discussion, when tail dispatching is enabled, Dispatch() doesn't queue the task in the event queue of the target thread immediately, instead the task is stored in the tail dispatcher queue and the real dispatching happens in the tail dispatching phase.

So this is not a bug, but just the way it works.

Comment 2

[Kilik Kuo [:kikuo] (inactive)]

Thanks for the explanation.