RFR: 8257831: Suspend with handshakes [v2]

[Patricio Chilano Mateo]

On Tue, 30 Mar 2021 13:26:13 GMT, Richard Reingruber <rrich 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 two commits:
>> 
>>  - Merge branch 'master' into SuspendInHandshake
>>  - 8257831: Suspend with handshake (review baseline)
>
> src/hotspot/share/runtime/handshake.hpp line 142:
> 
>> 140:  private:
>> 141:   volatile bool _suspended;
>> 142:   volatile bool _suspend_requested;
> 
> According to the PR description `_suspend_requested` is an optimization.
> 
>> The "suspend requested" flag is an optimization, without it a dormant thread
>> could be suspended and resumed many times and each would add a new
>> asynchronous handshake. Suspend requested flag means there is already an
>> asynchronous suspend handshake in queue which can be re-used, only the suspend
>> flag needs to be set.
> 
> I think there are a few places where _suspend_requested is queried by mistake instead of _suspended. Maybe it would help to prevent this if _suspend_requested was renamed to something that better describes its purpose, e.g. _has_async_suspend_handshake or similar.

I also think it would be a good idea to rename it with something along those lines.

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