Fix race on demuxer memory usage. Reuse previous calculation.

Fix race on demuxer memory usage. Reuse previous calculation.

GetMemoryUsage() is called from the render thread, so access to
FFmpegDemuxer internals must be procted.  Adding locking everywhere
would be a big change, so simply cache the last value when a new
packet is added and protect it via a lock.

BUG=550375
TEST=all tests pass, no tsan issue.

Committed: https://crrev.com/9ac642d1d2ed95b810ff276fb65c2be7b461e791
Cr-Commit-Position: refs/heads/master@{#357464}

[DaleCurtis, 2015-11-02 19:50:25]

Description was changed from

==========
Fix race on demuxer memory usage. Reuse previous calculation.

GetMemoryUsage() is called from the render thread, so access to
FFmpegDemuxer internals must be procted.  Adding locking everywhere
would be a big change, so simply cache the last value as is already
calculated by IsMaxMemoryUsageReached() and protect it via a lock.

BUG=550375
TEST=all tests pass, no tsan issue.
==========

to

==========
Fix race on demuxer memory usage. Reuse previous calculation.

GetMemoryUsage() is called from the render thread, so access to
FFmpegDemuxer internals must be procted.  Adding locking everywhere
would be a big change, so simply cache the last value as is already
calculated by IsMaxMemoryUsageReached() (which is called for every
packet added) and protect it via a lock.

BUG=550375
TEST=all tests pass, no tsan issue.
==========

[DaleCurtis, 2015-11-02 19:50:25]

dalecurtis@chromium.org changed reviewers:
+ sandersd@chromium.org

[sandersd (OOO until July 31), 2015-11-02 20:13:26]

LGTM for fixing the issue, but it's strange to tie the memory statistic
computation to a method that should really be consuming the value (not to
mention that it's called irregularly and conditionally).

[DaleCurtis, 2015-11-02 20:21:00]

How about now? Clarified the naming a bit, calling is unchanged though since
those states don't matter.

[DaleCurtis, 2015-11-02 20:22:04]

Description was changed from

==========
Fix race on demuxer memory usage. Reuse previous calculation.

GetMemoryUsage() is called from the render thread, so access to
FFmpegDemuxer internals must be procted.  Adding locking everywhere
would be a big change, so simply cache the last value as is already
calculated by IsMaxMemoryUsageReached() (which is called for every
packet added) and protect it via a lock.

BUG=550375
TEST=all tests pass, no tsan issue.
==========

to

==========
Fix race on demuxer memory usage. Reuse previous calculation.

GetMemoryUsage() is called from the render thread, so access to
FFmpegDemuxer internals must be procted.  Adding locking everywhere
would be a big change, so simply cache the last value when a new
packet is added and protect it via a lock.

BUG=550375
TEST=all tests pass, no tsan issue.
==========

[sandersd (OOO until July 31), 2015-11-02 20:24:53]

lgtm

[DaleCurtis, 2015-11-02 22:12:03]

The CQ bit was checked by dalecurtis@chromium.org

[commit-bot: I haz the power, 2015-11-02 22:12:57]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1419753007/20001
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1419753007/20001

[commit-bot: I haz the power, 2015-11-02 23:12:33]

Committed patchset #2 (id:20001)

[commit-bot: I haz the power, 2015-11-02 23:13:59]

Patchset 2 (id:??) landed as
https://crrev.com/9ac642d1d2ed95b810ff276fb65c2be7b461e791
Cr-Commit-Position: refs/heads/master@{#357464}