RFR: 8257831: Suspend with handshakes [v6]

[Robbin Ehn]

On Tue, 13 Apr 2021 02:41:41 GMT, David Holmes <dholmes at openjdk.org> wrote:

>> Robbin Ehn has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains eight commits:
>> 
>>  - Merge branch 'master' into SuspendInHandshake
>>  - Review fixes 2
>>  - White space fixes
>>  - Merge branch 'master' into SuspendInHandshake
>>  - Review fixes
>>  - Merge branch 'master' into SuspendInHandshake
>>  - Merge branch 'master' into SuspendInHandshake
>>  - 8257831: Suspend with handshake (review baseline)
>
> src/hotspot/share/runtime/objectMonitor.cpp line 447:
> 
>> 445:     // Completed the tranisition.
>> 446:     SafepointMechanism::process_if_requested(current);
>> 447:     current->set_thread_state(_thread_in_vm);
> 
> I feel very uncomfortable that we remain _thread_blocked_trans across such a lengthy chunk of code - particularly the call to exit()! This is an abuse of the trans states which are only supposed to exist and be used to ensure the correctness of the Dekker-duality when setting and reading the thread state.
> 
> And I still would prefer to see these state changes and related safepoint-mechanism checks encapsulated somehow.

Yes we should figure out something here.
Note that we use to call exit() while blocked.

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PR: https://git.openjdk.java.net/jdk/pull/3191