Question re safepoints and monitors

[Andrew Haley]

On 01/12/2012 12:39 PM, David Holmes wrote:
> Yes it is - the interpreter executes the monitorenter() call inside a 
> CALL_VM macro which checks for the pending exception.

Thanks, but I still don't quite get it.

The interrupting thread calls send_thread_stop(), which sets
thread._pending_async_exception:

  void set_pending_async_exception(oop e) {
    _pending_async_exception = e;
    _special_runtime_exit_condition = _async_exception;
    set_has_async_exception();
  }

As far as I can see the code that actually reads
thread._pending_async_exception and sets thread._pending_exception is
JavaThread::check_and_handle_async_exceptions():

  // Check for pending async. exception
  if (_pending_async_exception != NULL) {
    // Only overwrite an already pending exception, if it is not a threadDeath.
    if (!has_pending_exception() || !pending_exception()->is_a(SystemDictionary::ThreadDeath_klass())) {

      // We cannot call Exceptions::_throw(...) here because we cannot block
      set_pending_exception(_pending_async_exception, __FILE__, __LINE__);

but check_and_handle_async_exceptions() is not called in the case of a
monitor operation.  We need something to copy _pending_async_exception
to _pending_exception, but I can't see when that would ever be called.

Andrew.