RFR: 8238761: Asynchronous handshakes [v2]

[Robbin Ehn]

On Mon, 21 Sep 2020 05:17:03 GMT, David Holmes <dholmes at openjdk.org> wrote:

>> Robbin Ehn has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   Fixed double checks
>>   Added NSV
>>   ProcessResult to enum
>>   Fixed logging
>>   Moved _active_handshaker to private
>
> src/hotspot/share/runtime/handshake.cpp line 336:
> 
>> 334:   // and thus prevents reading stale data modified in the handshake closure
>> 335:   // by the Handshakee.
>> 336:   OrderAccess::acquire();
> 
> How/why is this deleted? Surely there are still single-thread VMops that use a handshake??

As I said in PR request:
"Removed VM_HandshakeOneThread, the VM thread uses the same call path as direct handshakes did."
They are not VM ops, and default we do not promise who will execute it.
Just that it will be executed on thread X.

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PR: https://git.openjdk.java.net/jdk/pull/151