VM: [GC] Array::MakeArray is racing with the sweeper.

VM: [GC] Array::MakeArray is racing with the sweeper.

Array::MakeArray can update tags and length of an array after tags were loaded by RawObject::Size() which leads to the inconsistency between size computed from these (stale) tags and SizeFromClass().

This race is benign in release mode and should only affect the assertion: if sweeper is using stale tags it will just think that a more memory is occupied by the array than it really occupies.

Fixes https://github.com/dart-lang/sdk/issues/27988

R=rmacnak@google.com

Committed: https://github.com/dart-lang/sdk/commit/e538af5a445ea03045b3d1de309283368591bbc2

[Vyacheslav Egorov (Google), 2017-01-21 18:34:23]

Description was changed from

==========
VM: [Precompiler] Perform GC when permuting class table in SortClasses.

We only update cids of live objects so sweeper might later encounter
incorrect cids when sweeping corpses.

In DropClasses perform GC both RELEASE and DEBUG mode - as incorrect
sweeping issue is not limited to DEBUG.

Fixes https://github.com/dart-lang/sdk/issues/27988
==========

to

==========
VM: [Precompiler] Perform GC when permuting class table in SortClasses.

We only update cids of live objects so sweeper might later encounter
incorrect cids when sweeping corpses.

In DropClasses perform GC both RELEASE and DEBUG mode - as incorrect
sweeping issue is not limited to DEBUG.

Fixes https://github.com/dart-lang/sdk/issues/27988
==========

[Vyacheslav Egorov (Google), 2017-01-21 18:34:23]

vegorov@google.com changed reviewers:
+ rmacnak@google.com

[Vyacheslav Egorov (Google), 2017-01-21 18:34:34]

Hi Ryan, Please take a look, Thanks!

[Vyacheslav Egorov (Google), 2017-01-23 18:14:18]

Heap::VisitObjects which is used for renumbering actually enumerates all objects
(including corpses) so this fix should not fix anything. 

Disregard.

[Vyacheslav Egorov (Google), 2017-01-24 13:39:51]

Description was changed from

==========
VM: [Precompiler] Perform GC when permuting class table in SortClasses.

We only update cids of live objects so sweeper might later encounter
incorrect cids when sweeping corpses.

In DropClasses perform GC both RELEASE and DEBUG mode - as incorrect
sweeping issue is not limited to DEBUG.

Fixes https://github.com/dart-lang/sdk/issues/27988
==========

to

==========
VM: [GC] Array::MakeArray is racing with the sweeper.

Array::MakeArray can update tags and length of an array after tags were loaded
by RawObject::Size() which leads to the inconsistency between size computed from
these (stale) tags and SizeFromClass(). 

This race is benign in release mode and should only affect the assertion: if
sweeper is using stale tags it will just think that a more memory is occupied by
the array than it really occupies.

Fixes https://github.com/dart-lang/sdk/issues/27988
==========

[Vyacheslav Egorov (Google), 2017-01-24 13:39:51]

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

[Vyacheslav Egorov (Google), 2017-01-24 13:39:56]

PTAL

[rmacnak, 2017-01-24 17:50:34]

LGTM

[Vyacheslav Egorov (Google), 2017-01-30 11:04:27]

Description was changed from

==========
VM: [GC] Array::MakeArray is racing with the sweeper.

Array::MakeArray can update tags and length of an array after tags were loaded
by RawObject::Size() which leads to the inconsistency between size computed from
these (stale) tags and SizeFromClass(). 

This race is benign in release mode and should only affect the assertion: if
sweeper is using stale tags it will just think that a more memory is occupied by
the array than it really occupies.

Fixes https://github.com/dart-lang/sdk/issues/27988
==========

to

==========
VM: [GC] Array::MakeArray is racing with the sweeper.

Array::MakeArray can update tags and length of an array after tags were loaded
by RawObject::Size() which leads to the inconsistency between size computed from
these (stale) tags and SizeFromClass().

This race is benign in release mode and should only affect the assertion: if
sweeper is using stale tags it will just think that a more memory is occupied by
the array than it really occupies.

Fixes https://github.com/dart-lang/sdk/issues/27988

R=rmacnak@google.com

Committed:
https://github.com/dart-lang/sdk/commit/e538af5a445ea03045b3d1de309283368591bbc2
==========

[Vyacheslav Egorov (Google), 2017-01-30 11:04:29]

Committed patchset #2 (id:20001) manually as
e538af5a445ea03045b3d1de309283368591bbc2 (presubmit successful).