1145686 - Enforce that MDSM state changes only happen on the state machine task queue

Status: RESOLVED FIXED

(Core :: Audio/Video, defect)

Description

[Bobby Holley (:bholley)]

Doing it any other way is totally insane. Once bug 1136873 lands I think we can fix things up so that this invariant holds.

Comment 1

[Bobby Holley (:bholley)]

https://treeherder.mozilla.org/#/jobs?repo=try&revision=7b5a2d2b3d1c

Comment 2

[Bobby Holley (:bholley)]

https://treeherder.mozilla.org/#/jobs?repo=try&revision=17917d70d602

Comment 3

[Bobby Holley (:bholley)]

Attachment: Part 1 - Make MDSM::Shutdown happen on the state machine thread. v1

Comment 4

[Bobby Holley (:bholley)]

Attachment: Part 2 - Make MDSM::StartBuffering happen on the state machine thread. v1

Comment 5

[Bobby Holley (:bholley)]

Attachment: Part 3 - Assert state machine thread for SetState. v1

We assert in CheckInDecodeComplete as well for good measure, since that's the
last caller of SetState that doesn't already assert it.

Comment 6

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

Comment on attachment 8582861 [details] [diff] [review]
Part 2 - Make MDSM::StartBuffering happen on the state machine thread. v1

Review of attachment 8582861 [details] [diff] [review]:
-----------------------------------------------------------------

::: dom/media/MediaDecoder.cpp
@@ +1498,5 @@
>    if (mResource) {
>      mResource->Resume();
>    }
>    if (aForceBuffering) {
>      ReentrantMonitorAutoEnter mon(GetReentrantMonitor());

Do we still need this monitor? We should be able to read/write |mDecoderStateMachine| on the main thread without the monitor.

@@ +1502,5 @@
>      ReentrantMonitorAutoEnter mon(GetReentrantMonitor());
>      if (mDecoderStateMachine) {
> +      RefPtr<nsRunnable> r =
> +        NS_NewRunnableMethod(mDecoderStateMachine, &MediaDecoderStateMachine::StartBuffering);
> +      mDecoderStateMachine->TaskQueue()->Dispatch(r.forget());

I would prefer to do the dispatch inside StartBuffering() to hide the details about threading model employed by MDSM. As far as MediaDecoder can see, MediaDecoderStateMachine::StartBuffering() should be a thread-safe function.

Comment 7

[Bobby Holley (:bholley)]

Attachment: Part 1 - Make MDSM::Shutdown happen on the state machine thread. v2

Comment 8

[Bobby Holley (:bholley)]

Attachment: Part 2 - Make MDSM::StartBuffering happen on the state machine thread. v2

Comment 9

[Bobby Holley (:bholley)]

Comment on attachment 8582862 [details] [diff] [review]
Part 3 - Assert state machine thread for SetState. v1

In general, feel free to do a drive-by r+ on state machine patches. :-)

Comment 10

[Bobby Holley (:bholley)]

Attachment: Part 4 - Dispatch all audiosink notifications asynchronously. v1

Per jww's suggestion.

Comment 11

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

Comment on attachment 8582898 [details] [diff] [review]
Part 4 - Dispatch all audiosink notifications asynchronously. v1

Review of attachment 8582898 [details] [diff] [review]:
-----------------------------------------------------------------

LGTM. Btw, MediaDecoder::UpdatePlaybackOffset() can now assert instead of acquiring the monitor. Stricter check makes it less likely to go unexpected.

Comment 12

[Bobby Holley (:bholley)]

So I did a try push of all of these patches: https://treeherder.mozilla.org/#/jobs?repo=try&revision=d40c2e06cd66

There was one failure in test_loop.html, which I confirmed to be caused by the topmost patch:
https://treeherder.mozilla.org/#/jobs?repo=try&revision=5b1b04b6ad68
https://treeherder.mozilla.org/#/jobs?repo=try&revision=855887ee7041

I split the topmost patch out into bug 1148571, and am going to push the rest of the patches here.

Comment 13

[Bobby Holley (:bholley)]

(the topmost patch was an extra "nice to have" suggestion by jww, and not really intrinsic to this bug to begin with)

Comment 14

[Bobby Holley (:bholley)]

remote:   https://hg.mozilla.org/integration/mozilla-inbound/rev/18af605c42d2
remote:   https://hg.mozilla.org/integration/mozilla-inbound/rev/954ec67d86f4
remote:   https://hg.mozilla.org/integration/mozilla-inbound/rev/e5c5a0f31dbe

Comment 15

[Phil Ringnalda (:philor)]

https://hg.mozilla.org/mozilla-central/rev/18af605c42d2
https://hg.mozilla.org/mozilla-central/rev/954ec67d86f4
https://hg.mozilla.org/mozilla-central/rev/e5c5a0f31dbe