[merge m59] [Sync] Refactor ModelSafeWorker::DoWorkAndWaitUntilDone() to avoid code duplication.

[merge m59] [Sync] Refactor ModelSafeWorker::DoWorkAndWaitUntilDone() to avoid code duplication.

Before this CL, logic to wait for a WorkCallback to run or be
abandoned was duplicated in multiple
ModelSafeWorker::DoWorkAndWaitUntilDoneImpl() implementations.

With this CL, ModelSafeWorker::DoWorkAndWaitUntilDoneImpl() is
replaced with ModelSafeWorker::ScheduleWork(). Implementations
are merely responsible for scheduling the callback that they
receive; they don't have to wait for it to run or be abandoned.

The logic to wait for the callback to run or be abandoned is moved
into ModelSafeWorker::DoWorkAndWaitUntilDone().
ModelSafeWorker::DoWorkAndWaitUntilDone() calls
ModelSafeWorker::ScheduleWork(). Then, it waits until either the
callback that it passed to ModelSafeWorker::ScheduleWork() is deleted
(may or may not have run) or ModelSafeWorker::RequestStop() is called
before the callback has started to run. Additionnaly, calling
ModelSafeWorker::RequestStop() transforms into no-op further
invocations of callbacks passed to ModelSafeWorker::ScheduleWork().

Unblocking ModelSafeWorker::DoWorkAndWaitUntilDone() when
ModelSafeWorker::RequestStop() is called is important to
prevent deadlocks in workers that schedule work on the UI
thread. Indeed, in Chrome, no tasks are scheduled on the UI
thread after ModelSafeWorker::RequestStop() is called and
pending UI tasks are not scheduled until after the sync thread
is joined.

BUG=663600
Review-Url: https://codereview.chromium.org/2782573002
Cr-Original-Commit-Position: refs/heads/master@{#463413}
Committed: https://chromium.googlesource.com/chromium/src/+/316c08f3692150ac1c416c67391768622cc6a77f
Review-Url: https://codereview.chromium.org/2782573002
Cr-Commit-Position: refs/heads/master@{#465229}
(cherry picked from commit eeeb0d0ec28227aba875195e0f20076414fc4596)

Review-Url: https://codereview.chromium.org/2848903002 .
Cr-Commit-Position: refs/branch-heads/3071@{#292}
Cr-Branched-From: a106f0abbf69dad349d4aaf4bcc4f5d376dd2377-refs/heads/master@{#464641}
Committed: https://chromium.googlesource.com/chromium/src/+/6927834a532c164dc1899ff7f0c549eae2dbe7a3

[fdoray, 2017-04-28 14:45:03]

Description was changed from

==========
[merge m59] [Sync] Refactor ModelSafeWorker::DoWorkAndWaitUntilDone() to avoid
code duplication.

Before this CL, logic to wait for a WorkCallback to run or be
abandoned was duplicated in multiple
ModelSafeWorker::DoWorkAndWaitUntilDoneImpl() implementations.

With this CL, ModelSafeWorker::DoWorkAndWaitUntilDoneImpl() is
replaced with ModelSafeWorker::ScheduleWork(). Implementations
are merely responsible for scheduling the callback that they
receive; they don't have to wait for it to run or be abandoned.

The logic to wait for the callback to run or be abandoned is moved
into ModelSafeWorker::DoWorkAndWaitUntilDone().
ModelSafeWorker::DoWorkAndWaitUntilDone() calls
ModelSafeWorker::ScheduleWork(). Then, it waits until either the
callback that it passed to ModelSafeWorker::ScheduleWork() is deleted
(may or may not have run) or ModelSafeWorker::RequestStop() is called
before the callback has started to run. Additionnaly, calling
ModelSafeWorker::RequestStop() transforms into no-op further
invocations of callbacks passed to ModelSafeWorker::ScheduleWork().

Unblocking ModelSafeWorker::DoWorkAndWaitUntilDone() when
ModelSafeWorker::RequestStop() is called is important to
prevent deadlocks in workers that schedule work on the UI
thread. Indeed, in Chrome, no tasks are scheduled on the UI
thread after ModelSafeWorker::RequestStop() is called and
pending UI tasks are not scheduled until after the sync thread
is joined.

BUG=663600

Review-Url: https://codereview.chromium.org/2782573002
Cr-Original-Commit-Position: refs/heads/master@{#463413}
Committed:
https://chromium.googlesource.com/chromium/src/+/316c08f3692150ac1c416c673917...
Review-Url: https://codereview.chromium.org/2782573002
Cr-Commit-Position: refs/heads/master@{#465229}
(cherry picked from commit eeeb0d0ec28227aba875195e0f20076414fc4596)
==========

to

==========
[merge m59] [Sync] Refactor ModelSafeWorker::DoWorkAndWaitUntilDone() to avoid
code duplication.

Before this CL, logic to wait for a WorkCallback to run or be
abandoned was duplicated in multiple
ModelSafeWorker::DoWorkAndWaitUntilDoneImpl() implementations.

With this CL, ModelSafeWorker::DoWorkAndWaitUntilDoneImpl() is
replaced with ModelSafeWorker::ScheduleWork(). Implementations
are merely responsible for scheduling the callback that they
receive; they don't have to wait for it to run or be abandoned.

The logic to wait for the callback to run or be abandoned is moved
into ModelSafeWorker::DoWorkAndWaitUntilDone().
ModelSafeWorker::DoWorkAndWaitUntilDone() calls
ModelSafeWorker::ScheduleWork(). Then, it waits until either the
callback that it passed to ModelSafeWorker::ScheduleWork() is deleted
(may or may not have run) or ModelSafeWorker::RequestStop() is called
before the callback has started to run. Additionnaly, calling
ModelSafeWorker::RequestStop() transforms into no-op further
invocations of callbacks passed to ModelSafeWorker::ScheduleWork().

Unblocking ModelSafeWorker::DoWorkAndWaitUntilDone() when
ModelSafeWorker::RequestStop() is called is important to
prevent deadlocks in workers that schedule work on the UI
thread. Indeed, in Chrome, no tasks are scheduled on the UI
thread after ModelSafeWorker::RequestStop() is called and
pending UI tasks are not scheduled until after the sync thread
is joined.

BUG=663600

Review-Url: https://codereview.chromium.org/2782573002
Cr-Original-Commit-Position: refs/heads/master@{#463413}
Committed:
https://chromium.googlesource.com/chromium/src/+/316c08f3692150ac1c416c673917...
Review-Url: https://codereview.chromium.org/2782573002
Cr-Commit-Position: refs/heads/master@{#465229}
(cherry picked from commit eeeb0d0ec28227aba875195e0f20076414fc4596)

Review-Url: https://codereview.chromium.org/2848903002 .
Cr-Commit-Position: refs/branch-heads/3071@{#292}
Cr-Branched-From:
a106f0abbf69dad349d4aaf4bcc4f5d376dd2377-refs/heads/master@{#464641}
Committed:
https://chromium.googlesource.com/chromium/src/+/6927834a532c164dc1899ff7f0c5...
==========

[fdoray, 2017-04-28 14:45:05]

Committed patchset #1 (id:1) manually as
6927834a532c164dc1899ff7f0c549eae2dbe7a3.