P4
If suspension is allowed when a thread is re-entering an object monitor (OM), then a deadlock is possible in two cases:
1) The waiting thread is made to be a successor and is unparked. Upon a suspension request, the thread will suspend itself whilst clearing the successor. The OM will be left unlocked (not grabbed by any thread), while the other threads are parked until a thread grabs the OM and the exits it. The suspended thread is on the entry-list and can be selected as a successor again. None of other threads can be woken up to grab the OM until the suspended thread has been resumed and successfully releases the OM.
2) The race between suspension and retry: the thread could reacquire the OM and complete the wait() code in full, but then on return to Java it will be suspended while holding the OM.
1) The waiting thread is made to be a successor and is unparked. Upon a suspension request, the thread will suspend itself whilst clearing the successor. The OM will be left unlocked (not grabbed by any thread), while the other threads are parked until a thread grabs the OM and the exits it. The suspended thread is on the entry-list and can be selected as a successor again. None of other threads can be woken up to grab the OM until the suspended thread has been resumed and successfully releases the OM.
2) The race between suspension and retry: the thread could reacquire the OM and complete the wait() code in full, but then on return to Java it will be suspended while holding the OM.