Blocking local sense synchronization barrier

A blocking local sense synchronization barrier is provided. The local sense variable is not processor private or global, but truly local to the synchronization barrier function. Safe deletion is provided by making sure the last operation a thread performs on a barrier is a write. Just before returning, threads increment a field that indicates the count of threads that have left the barrier. Blocking is supported such that threads spin for some interval, and when they decide to block, examine and set (if not already set) the indication of whether a thread is blocking that is to be examined by the last thread to arrive at the barrier to determine whether to set an event to release blocking threads.