RFR: 8223312: Utilize handshakes instead of is_thread_fully_suspended [v3]

[Richard Reingruber]

On Wed, 21 Oct 2020 17:03:45 GMT, Daniel D. Daugherty <dcubed at openjdk.org> wrote:

>> src/hotspot/share/prims/jvmtiEnvBase.cpp line 1454:
>> 
>>> 1452:   _state->set_earlyret_pending();
>>> 1453:   _state->set_earlyret_oop(ret_ob_h());
>>> 1454:   _state->set_earlyret_value(_value, _tos);
>> 
>> Good that these updates are done with a handshake now. Maybe I'm missing s.th. but I don't see synchronization in the older version.
>
> Agreed. @sspitsyn - This makes me wonder if the lack of
> synchronization is the cause of some instability in the
> JVM/TI ForceEarlyReturn() testing.
> 
> Update: The old code only made the updates if the thread was fully
> suspended so you won't have a race between the requesting thread
> and the target thread in that case.

Yes, I meant synchronization between racing agent threads. Surely a corner case.

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PR: https://git.openjdk.java.net/jdk/pull/729