Introduce a new phantom weakness type without finalization callback.

Introduce a new phantom weakness type without finalization callback.
Handles of this type are automatically reset by the garbage collector
when their objects are not longer reachable.

The motivation is to reduce pause time of external.weak_global_handles
phase of the garbage collector by not maintaing the list of pending
callbacks and not calling the callbacks.

Local testing on discourse page of the v8.inifinite_scroll benchmark
shows 7x improvement for this GC phase.

Before:
external.weak_global_handles
 len: 21
 min: 0.0
 max: 4.5
 avg: 0.757142857143

After:
external.weak_global_handles
 len: 21
 min: 0.0
 max: 0.5
 avg: 0.109523809524

A follow-up patch will enable the new phantom handles in Chromium.

BUG=chromium:608333
LOG=NO

Committed: https://crrev.com/a6da98d86ffab7e1e50319ed12b57fcb366e24ee
Cr-Commit-Position: refs/heads/master@{#36095}

[ulan, 2016-05-04 13:55:39]

Description was changed from

==========
Introduce a new phantom weakness type without finalization callback.
Handles of this type are automatically reset by the garbage collector
when their objects are not longer reachable.

The motivation is to reduce pause time of external.weak_global_handles
phase of the garbage collector by not maintaing the list of pending
callbacks and not calling the callbacks.

Local testing on Discourse page of the v8.inifinite_scroll benchmark
shows 7x improvement for this GC phase.

Before:
external.weak_global_handles
 len: 21
 min: 0.0
 max: 4.5
 avg: 0.757142857143

After:
external.weak_global_handles
 len: 21
 min: 0.0
 max: 0.5
 avg: 0.109523809524

A follow-up patch will enable the new phantom handles in Chromium.

BUG=chromium:608333
LOG=NO
==========

to

==========
Introduce a new phantom weakness type without finalization callback.
Handles of this type are automatically reset by the garbage collector
when their objects are not longer reachable.

The motivation is to reduce pause time of external.weak_global_handles
phase of the garbage collector by not maintaing the list of pending
callbacks and not calling the callbacks.

Local testing on discourse page of the v8.inifinite_scroll benchmark
shows 7x improvement for this GC phase.

Before:
external.weak_global_handles
 len: 21
 min: 0.0
 max: 4.5
 avg: 0.757142857143

After:
external.weak_global_handles
 len: 21
 min: 0.0
 max: 0.5
 avg: 0.109523809524

A follow-up patch will enable the new phantom handles in Chromium.

BUG=chromium:608333
LOG=NO
==========

[ulan, 2016-05-04 13:56:54]

ulan@chromium.org changed reviewers:
+ jochen@chromium.org

[ulan, 2016-05-04 13:56:54]

ptal

[jochen (gone - plz use gerrit), 2016-05-04 14:50:04]

lgtm

[ulan, 2016-05-04 15:30:44]

Turns out we don't have enough bits in flag_ to afford adding a new weakness
type PHANTOM_WEAK_RESET_HANDLE.

I am now encoding it as PHANTOM_WEAK with weak_callback_ == nullptr. Not ideal,
but the alternative is to increase flags size.

[jochen (gone - plz use gerrit), 2016-05-04 15:48:38]

On 2016/05/04 at 15:30:44, ulan wrote:
> Turns out we don't have enough bits in flag_ to afford adding a new weakness
type PHANTOM_WEAK_RESET_HANDLE.
> 
> I am now encoding it as PHANTOM_WEAK with weak_callback_ == nullptr. Not
ideal, but the alternative is to increase flags size.

We could also consider ripping out normal_weak now that we have finalized_weak

[ulan, 2016-05-04 15:59:21]

On 2016/05/04 15:48:38, jochen wrote:
> On 2016/05/04 at 15:30:44, ulan wrote:
> > Turns out we don't have enough bits in flag_ to afford adding a new weakness
> type PHANTOM_WEAK_RESET_HANDLE.
> > 
> > I am now encoding it as PHANTOM_WEAK with weak_callback_ == nullptr. Not
> ideal, but the alternative is to increase flags size.
> 
> We could also consider ripping out normal_weak now that we have finalized_weak

Good point. I see that SetWeak with WeakCallbackData is already deprecated.

I'll remove normal weak.

[ulan, 2016-05-06 13:42:59]

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

[commit-bot: I haz the power, 2016-05-06 13:43:06]

Dry run: CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1950963002/60001
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1950963002/60001

[commit-bot: I haz the power, 2016-05-06 14:12:18]

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

[commit-bot: I haz the power, 2016-05-06 14:12:19]

Dry run: This issue passed the CQ dry run.

[ulan, 2016-05-09 06:32:01]

The CQ bit was checked by ulan@chromium.org

[ulan, 2016-05-09 06:32:01]

The patchset sent to the CQ was uploaded after l-g-t-m from jochen@chromium.org
Link to the patchset: https://codereview.chromium.org/1950963002/#ps60001
(title: "comment")

[commit-bot: I haz the power, 2016-05-09 06:32:10]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1950963002/60001
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1950963002/60001

[commit-bot: I haz the power, 2016-05-09 07:15:52]

Description was changed from

==========
Introduce a new phantom weakness type without finalization callback.
Handles of this type are automatically reset by the garbage collector
when their objects are not longer reachable.

The motivation is to reduce pause time of external.weak_global_handles
phase of the garbage collector by not maintaing the list of pending
callbacks and not calling the callbacks.

Local testing on discourse page of the v8.inifinite_scroll benchmark
shows 7x improvement for this GC phase.

Before:
external.weak_global_handles
 len: 21
 min: 0.0
 max: 4.5
 avg: 0.757142857143

After:
external.weak_global_handles
 len: 21
 min: 0.0
 max: 0.5
 avg: 0.109523809524

A follow-up patch will enable the new phantom handles in Chromium.

BUG=chromium:608333
LOG=NO
==========

to

==========
Introduce a new phantom weakness type without finalization callback.
Handles of this type are automatically reset by the garbage collector
when their objects are not longer reachable.

The motivation is to reduce pause time of external.weak_global_handles
phase of the garbage collector by not maintaing the list of pending
callbacks and not calling the callbacks.

Local testing on discourse page of the v8.inifinite_scroll benchmark
shows 7x improvement for this GC phase.

Before:
external.weak_global_handles
 len: 21
 min: 0.0
 max: 4.5
 avg: 0.757142857143

After:
external.weak_global_handles
 len: 21
 min: 0.0
 max: 0.5
 avg: 0.109523809524

A follow-up patch will enable the new phantom handles in Chromium.

BUG=chromium:608333
LOG=NO
==========

[commit-bot: I haz the power, 2016-05-09 07:15:53]

Committed patchset #4 (id:60001)

[commit-bot: I haz the power, 2016-05-09 07:18:07]

Description was changed from

==========
Introduce a new phantom weakness type without finalization callback.
Handles of this type are automatically reset by the garbage collector
when their objects are not longer reachable.

The motivation is to reduce pause time of external.weak_global_handles
phase of the garbage collector by not maintaing the list of pending
callbacks and not calling the callbacks.

Local testing on discourse page of the v8.inifinite_scroll benchmark
shows 7x improvement for this GC phase.

Before:
external.weak_global_handles
 len: 21
 min: 0.0
 max: 4.5
 avg: 0.757142857143

After:
external.weak_global_handles
 len: 21
 min: 0.0
 max: 0.5
 avg: 0.109523809524

A follow-up patch will enable the new phantom handles in Chromium.

BUG=chromium:608333
LOG=NO
==========

to

==========
Introduce a new phantom weakness type without finalization callback.
Handles of this type are automatically reset by the garbage collector
when their objects are not longer reachable.

The motivation is to reduce pause time of external.weak_global_handles
phase of the garbage collector by not maintaing the list of pending
callbacks and not calling the callbacks.

Local testing on discourse page of the v8.inifinite_scroll benchmark
shows 7x improvement for this GC phase.

Before:
external.weak_global_handles
 len: 21
 min: 0.0
 max: 4.5
 avg: 0.757142857143

After:
external.weak_global_handles
 len: 21
 min: 0.0
 max: 0.5
 avg: 0.109523809524

A follow-up patch will enable the new phantom handles in Chromium.

BUG=chromium:608333
LOG=NO

Committed: https://crrev.com/a6da98d86ffab7e1e50319ed12b57fcb366e24ee
Cr-Commit-Position: refs/heads/master@{#36095}
==========

[commit-bot: I haz the power, 2016-05-09 07:18:08]

Patchset 4 (id:??) landed as
https://crrev.com/a6da98d86ffab7e1e50319ed12b57fcb366e24ee
Cr-Commit-Position: refs/heads/master@{#36095}