Fix some potential data races based on output from tsan.

Fix some potential data races based on output from tsan.

R=zra@google.com

Committed: https://github.com/dart-lang/sdk/commit/c45ebeba70f6e67e0c5fb414995e55cf3436f6c3

[siva, 2016-03-03 23:46:14]

asiva@google.com changed reviewers:
+ zra@google.com

[zra, 2016-03-03 23:50:02]

lgtm w/ question

https://codereview.chromium.org/1765533003/diff/1/runtime/vm/class_table.cc
File runtime/vm/class_table.cc (right):

https://codereview.chromium.org/1765533003/diff/1/runtime/vm/class_table.cc#n...
runtime/vm/class_table.cc:112: ASSERT(Object::builtin_vtables_[index] ==
cls_vtable);
Is this asserting that the compare and swap was successful? Doesn't
CompareAndSwap return something to indicate success?

[siva, 2016-03-04 20:53:29]

https://codereview.chromium.org/1765533003/diff/1/runtime/vm/class_table.cc
File runtime/vm/class_table.cc (right):

https://codereview.chromium.org/1765533003/diff/1/runtime/vm/class_table.cc#n...
runtime/vm/class_table.cc:112: ASSERT(Object::builtin_vtables_[index] ==
cls_vtable);
On 2016/03/03 23:50:02, zra wrote:
> Is this asserting that the compare and swap was successful? Doesn't
> CompareAndSwap return something to indicate success?

The ASSERT is to make sure the value of builtin_vtables_[index] is not 0 after
the CAS.

The CompareAndSwap function returns the old value in the location which could be
0 or cls_vtable depending on whether the CAS stored cls_vtable or it already had
cls_vtable in that location.

[siva, 2016-03-04 21:35:28]

Description was changed from

==========
Fix some potential data races based on output from tsan.
==========

to

==========
Fix some potential data races based on output from tsan.

R=zra@google.com

Committed:
https://github.com/dart-lang/sdk/commit/c45ebeba70f6e67e0c5fb414995e55cf3436f6c3
==========

[siva, 2016-03-04 21:35:30]

Committed patchset #1 (id:1) manually as
c45ebeba70f6e67e0c5fb414995e55cf3436f6c3 (presubmit successful).