RFR: 8286830: ~HandshakeState should not touch oops

[David Holmes]

On Thu, 19 May 2022 19:17:09 GMT, Patricio Chilano Mateo <pchilanomate at openjdk.org> wrote:

> On 8284632 we added ~HandshakeState to cleanup any potential async operations left in the handshake queue. This could trigger the release of an oophandle from its associated oop-storage when trying to delete an AsyncExceptionHandshake object. Since the exiting JT already executed on_thread_detach() this is forbidden. 
> To fix this I used the original approach that @dcubed-ojdk posted on the 8284632 fix, which is cleaning up those operations before on_thread_detach() is executed. To make sure that no other async exception operation is added to the queue after that I did two things:
> - Added a check in install_async_exception() to avoid installing the operation if the target already moved to the _thread_exiting state.
> - Move the setting of the _thread_exiting state to include the case where JavaThread::exit() is called with destroy_vm=true.
> 
> I also added another run to tests StopAtExit.java and SuspendAtExit.java with extra contention on the Threads_lock. That increases the odds of the target being handshake safe while being in the _thread_exiting state which allows testing for more pathological cases.
> 
> I was able to reproduce the issue by running StopAtExit.java with -XX:+UseShenandoahGC and verified that the test now passes. I also run mach5 tiers1-3. Will run the upper tiers also and will do an additional pass after that.
> 
> Thanks,
> Patricio

src/hotspot/share/runtime/thread.cpp line 1443:

> 1441:   // we can just put in the exiting state and it will be correctly handled.
> 1442:   // Also, no more async exceptions will be added to the queue after this point.
> 1443:   set_terminated(_thread_exiting);

I would have expected that cleaning up any async exceptions has to happen after we set the _thread_exiting state; otherwise what happens if another thread is trying to install an async exception on the current thread before we set it?

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PR: https://git.openjdk.java.net/jdk/pull/8795