Question re safepoints and monitors

[Andrew Haley]

This is re HS20 on Zero, but it might apply to any HotSpot port AFAIK.

We invoke Thread.stop on a thread.  To do this, we need to wait for
the thread to reach a safepoint.  So, thread->set_pending_exception()
is called, and SafepointSynchronize::_state is set to
SafepointSynchronize::_synchronizing.

The thread needs to acquire a lock, so it enters
InterpreterRuntime::monitorenter().  This does the safepoint check.
monitorenter() is marked IRT_ENTRY_NO_ASYNC, so it does not check for
pending async exceptions.  Control returns from monitorenter and the
thread continues to execute Java.  The async exception is not
processed.

As far as I can see, there is still a pending exception for this
thread but it won't be processed until something else causes the
thread to move to a safepoint.  Is that right?

Thanks,
Andrew.