Question re safepoints and monitors

[David Holmes]

Andrew,

On 12/01/2012 9:53 PM, Andrew Haley wrote:
> 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.

Yes it is - the interpreter executes the monitorenter() call inside a 
CALL_VM macro which checks for the pending exception.

David
-----

> 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.