1727262 - MediaEventSource can cause shutdown hangs

Status: RESOLVED FIXED

(Core :: Audio/Video: Playback, task, P2)

Description

[Andreas Pehrson [:pehrsons]]

This is similar to bug 1702823 but for mTarget instead of mFunction.

The solution cannot be the same, since Notify() needs mTarget, and syncing this through revocation status is impossible (races) unless we switch to a Mutex. mFunctionWrapper could be removed on the target thread since that's where revocation happens.

Prerequisites:

• A MediaEventListener target that sits on top of a SharedThreadPool, for instance a TaskQueue (common), where the target's shutdown sequence is triggered by destruction, i.e., all hard refs to it are removed (probably not so common)
• A MediaEventProducer owned by a garbage collected object

Example sequence causing a shutdown hang:

• Listener is hooked up to the source
• XPCOM shutdown
• Listener is revoked (clearing the function but not the target)
• The MediaEventProducer owner is part of a ref-cycle and although CCed, lives on to CC-shutdown, which is after xpcom-shutdown-threads
• xpcom-shutdown-threads is blocked on a SharedThreadPool being alive

Comment 1

[Andreas Pehrson [:pehrsons]]

Attachment: Bug 1727262 - Ensure MediaEventListener revocation clears all members to prevent shutdown hangs. r?alwu!, r?bryce!

Comment 2

[Andreas Pehrson [:pehrsons]]

Attachment: Bug 1727262 - Add gtest. r?alwu!

Comment 3

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/0b8b1d0ee784
Add gtest. r=alwu
https://hg.mozilla.org/integration/autoland/rev/46173dc5f5e6
Ensure MediaEventListener revocation clears all members to prevent shutdown hangs. r=alwu,bryce

Comment 4

[Sandor Molnar]

https://hg.mozilla.org/mozilla-central/rev/0b8b1d0ee784
https://hg.mozilla.org/mozilla-central/rev/46173dc5f5e6