1398700 - Data race in updating mChannelOffset when MediaCacheStream::NotifyDataReceived() runs off the main thread

Status: RESOLVED WONTFIX

(Core :: Audio/Video: Playback, enhancement, P3)

Description

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

http://searchfox.org/mozilla-central/rev/00fa5dacedb925022f53d025121f1a919508e7ce/dom/media/MediaCache.h#446-448,463

mChannelOffset can only be updated on the main thread and with the monitor held.

We will make it safe to read/write on any thread.

Comment 1

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

Attachment: Bug 1398700. P1 - fix the data race in reading mChannelOffset in Update() without holding the lock.

It is a data race to read mChannelOffset in Update() without holding the lock
if NotifyDataReceived() runs off the main thread. We fix the race by introducing
mClientSeeking to freeze mChannelOffset so it is safe to read mChannelOffset
without holding the lock.

mClientSeeking is also used in NotifyDataReceived() to prevent data from
going to the wrong position.

Review commit: https://reviewboard.mozilla.org/r/179062/diff/#index_header
See other reviews: https://reviewboard.mozilla.org/r/179062/

Comment 2

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

Attachment: Bug 1398700. P2 - make mChannelOffset safe to read/write on any thread.

The only exception is that it is safe to read mChannelOffset without lock
when mClientSeeking is true.

Review commit: https://reviewboard.mozilla.org/r/179064/diff/#index_header
See other reviews: https://reviewboard.mozilla.org/r/179064/