RFR: 8257831: Suspend with handshakes [v2]

[Robbin Ehn]

On Tue, 30 Mar 2021 15:50:56 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/objectMonitor.cpp line 973:
> 
>> 971:       if (SafepointMechanism::should_process(current)) {
>> 972:         if (_succ == current) {
>> 973:             _succ = NULL;
> 
> IIUC then this is now not only executed if a thread is suspended but also when there's a safepoint / handshake. I tried to understand the effect of this but failed with timeout ;)

On high-level clearing causes some extra work and contention when exiting.
Maybe we should think about just doing this when suspended.

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