RFR: 8257831: Suspend with handshakes [v2]

[Robbin Ehn]

On Wed, 31 Mar 2021 05:44:35 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 two commits:
>> 
>>  - Merge branch 'master' into SuspendInHandshake
>>  - 8257831: Suspend with handshake (review baseline)
>
> src/hotspot/share/runtime/handshake.cpp line 677:
> 
>> 675:     } else {
>> 676:       // Target is going to wake up and leave suspension.
>> 677:       // Let's just stop the thread from doing that.
> 
> IIUC this would be the case where the target was hit with a suspend request but has not yet processed the actual suspension handshake op, then a resume comes in so suspended is no longer true, and then another suspend request is made (this one) which simply turns the suspended flag back on - is that right?
> Overall I'm finding it very hard to see what the two suspend state flags actually signify. I'd like to see that written up somewhere.

Sure

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