RFR: 8319778: Remove unreachable code in ObjectSynchronizer::exit [v2]

[Daniel D. Daugherty]

On Tue, 14 Nov 2023 13:24:56 GMT, Axel Boldt-Christmas <aboldtch at openjdk.org> wrote:

>> In `ObjectSynchronizer::exit` when unlocking on an inflated monitor with `LM_LIGHTWEIGHT` there is a check if the owner is anonymous. That branch should never be take and would indicate that something is wrong with either `ObjectSynchronizer::inflate` or that `ObjectSynchronizer::exit` is trying to unlock a monitor not owned by the `current` thread.
>> 
>> Changes this to an assert instead. Did not condition the assert on `LM_LIGHTWEIGHT` as this property should hold regardless of locking mode.
>
> Axel Boldt-Christmas has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains two additional commits since the last revision:
> 
>  - Merge remote-tracking branch 'upstream_jdk/master' into JDK-8319778
>  - 8319778: Remove unreachable code in ObjectSynchronizer::exit

Thumbs up.

Please run Tier1 testing prior to integration if that has not yet been done.
I don't expect any issues on non-Linux platforms, but you never know...

src/hotspot/share/runtime/synchronizer.cpp line 641:

> 639:   // dropped inside exit() and the ObjectMonitor* must be !is_busy().
> 640:   ObjectMonitor* monitor = inflate(current, object, inflate_cause_vm_internal);
> 641:   assert(!monitor->is_owner_anonymous(), "must not be");

Agreed that the block from old L641 -> L647 is impossible after the call
to `inflate()` on L640. Thanks for adding that assert.

The other reason is if the owner came in here with a lightweight monitor,
then that would have been handled via L571 -> L592 and we never should
have reached this block.

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Marked as reviewed by dcubed (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/16602#pullrequestreview-1734906673
PR Review Comment: https://git.openjdk.org/jdk/pull/16602#discussion_r1396009774