RFR: 8257831: Suspend with handshakes [v3]

[Robbin Ehn]

On Wed, 7 Apr 2021 11:50:09 GMT, Robbin Ehn <rehn at openjdk.org> wrote:

>> src/hotspot/share/runtime/objectMonitor.cpp line 428:
>> 
>>> 426:       } else {
>>> 427:         // Only exit path from for loop
>>> 428:         SafepointMechanism::process_if_requested(current);
>> 
>> I think the current thread can suspend here in L428. This seems problematic as entering OM has been started but not completed.
>> 
>> - The current thread is set as owner in ObjectMonitor::_owner
>> - The thread state will still be JVMTI_THREAD_STATE_BLOCKED_ON_MONITOR_ENTER because of the JavaThreadBlockedOnMonitorEnterState in L389.
>> - Thread::_current_pending_monitor has not been reset to NULL.
>
> Yes, I think you are correct. I'll look over it.

Today the ThreadBlockInVM tbivm(current); is inside scope of JavaThreadBlockedOnMonitorEnterState jtbmes(current, this);.
So this can happen today also.

If you are context switch just before current->set_current_pending_monitor(NULL);.
Someone suspends you and look at those states.

If you agree that the issue is preexisting I prefer handling that outside scope of this.

-------------

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