Make CancelableTaskTracker sequence-safe.

Make CancelableTaskTracker sequence-safe.

This CL allows CancelableTaskTracker to be used from sequenced
tasks. Previously, it had to be used from a single thread.

BUG=675631
Committed: https://crrev.com/6661c527f2cc07652b208e05afd07b79baf58301
Cr-Commit-Position: refs/heads/master@{#440078}

[fdoray, 2016-12-20 13:41:20]

Description was changed from

==========
Make CancelableTaskTracker sequence-safe.

BUG=675631
==========

to

==========
Make CancelableTaskTracker sequence-safe.

This CL allows CancelableTaskTracker to be used from sequenced
tasks. Previously, it could only be used from single-threaded
tasks.

BUG=675631
==========

[fdoray, 2016-12-20 13:41:38]

Description was changed from

==========
Make CancelableTaskTracker sequence-safe.

This CL allows CancelableTaskTracker to be used from sequenced
tasks. Previously, it could only be used from single-threaded
tasks.

BUG=675631
==========

to

==========
Make CancelableTaskTracker sequence-safe.

This CL allows CancelableTaskTracker to be used from sequenced
tasks. Previously, it had to be used from a single thread.

BUG=675631
==========

[fdoray, 2016-12-20 13:46:57]

The CQ bit was checked by fdoray@chromium.org to run a CQ dry run

[commit-bot: I haz the power, 2016-12-20 13:47:03]

Dry run: CQ is trying da patch. Follow status at
 
https://chromium-cq-status.appspot.com/v2/patch-status/codereview.chromium.or...

[fdoray, 2016-12-20 13:47:44]

fdoray@chromium.org changed reviewers:
+ dcheng@chromium.org

[fdoray, 2016-12-20 13:47:44]

PTAL

[commit-bot: I haz the power, 2016-12-20 16:33:36]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2016-12-20 16:33:36]

Dry run: This issue passed the CQ dry run.

[dcheng, 2016-12-20 19:14:36]

This CL looks reasonable: just to confirm... are there any gotchas when
switching from sequence checker to thread checker or the other way around?

https://codereview.chromium.org/2586273002/diff/60001/base/task/cancelable_ta...
File base/task/cancelable_task_tracker.cc (left):

https://codereview.chromium.org/2586273002/diff/60001/base/task/cancelable_ta...
base/task/cancelable_task_tracker.cc:60: namespace base {
Oops.

[fdoray, 2016-12-20 20:14:34]

On 2016/12/20 19:14:36, dcheng wrote:
> This CL looks reasonable: just to confirm... are there any gotchas when
> switching from sequence checker to thread checker or the other way around?
> 

SequenceChecker::CalledOnValidSequence() returns true in all situations where
ThreadChecker::CalledOnValidThread() returns true [1]. Therefore,
s/ThreadChecker/SequenceChecker/ should not break existing code. However, it
allows new uses of CancelableTaskTracker from sequenced tasks. This is safe as
long as CancelableTaskTracker and callbacks posted through it don't depend on a
constant thread id (in particular, they should not use thread-local storage).


[1] Except when called from SWP tasks that happen to run on the same thread
despite being associated with different sequence tokens. Code that DCHECKs that
SWP tasks associated with different sequence tokens run on the same thread is
necessarily flaky.

[dcheng, 2016-12-21 04:28:36]

LGTM

Hopefully the use of TLS is pretty rare in Chrome.

[fdoray, 2016-12-21 12:57:37]

The CQ bit was checked by fdoray@chromium.org

[commit-bot: I haz the power, 2016-12-21 12:57:51]

CQ is trying da patch. Follow status at
 
https://chromium-cq-status.appspot.com/v2/patch-status/codereview.chromium.or...

[commit-bot: I haz the power, 2016-12-21 13:02:12]

CQ is committing da patch.

Bot data: {"patchset_id": 60001, "attempt_start_ts": 1482325057599930,
"parent_rev": "068fe2f867ac8b8e9ff4ad279a435f2cb04305e3", "commit_rev":
"ebc2d9648526e11692ea31a9842d359e99231524"}

[commit-bot: I haz the power, 2016-12-21 13:02:36]

Description was changed from

==========
Make CancelableTaskTracker sequence-safe.

This CL allows CancelableTaskTracker to be used from sequenced
tasks. Previously, it had to be used from a single thread.

BUG=675631
==========

to

==========
Make CancelableTaskTracker sequence-safe.

This CL allows CancelableTaskTracker to be used from sequenced
tasks. Previously, it had to be used from a single thread.

BUG=675631

Review-Url: https://codereview.chromium.org/2586273002
==========

[commit-bot: I haz the power, 2016-12-21 13:02:37]

Committed patchset #4 (id:60001)

[commit-bot: I haz the power, 2016-12-21 13:05:03]

Description was changed from

==========
Make CancelableTaskTracker sequence-safe.

This CL allows CancelableTaskTracker to be used from sequenced
tasks. Previously, it had to be used from a single thread.

BUG=675631

Review-Url: https://codereview.chromium.org/2586273002
==========

to

==========
Make CancelableTaskTracker sequence-safe.

This CL allows CancelableTaskTracker to be used from sequenced
tasks. Previously, it had to be used from a single thread.

BUG=675631

Committed: https://crrev.com/6661c527f2cc07652b208e05afd07b79baf58301
Cr-Commit-Position: refs/heads/master@{#440078}
==========

[commit-bot: I haz the power, 2016-12-21 13:05:04]

Patchset 4 (id:??) landed as
https://crrev.com/6661c527f2cc07652b208e05afd07b79baf58301
Cr-Commit-Position: refs/heads/master@{#440078}