The function int pthread_cancel(pthread_t thread); sends a request that 'thread' shall be canceled. The target thread's cancelability state and type determines when/if the cancelation takes effect. When the cancelation request is honored, the cancelation cleanup handlers for 'thread' are called. When the last cancelation cleanup handler returns, the thread-specific data destructer functions will be called for 'thread'. When the last destructer function returns, 'thread' then terminates. NOTE: Still trying to find a good way to test the second paragraph of assertion #2. The cancelation processing in the target thread will run asynchronously with respect to the calling thread returning from pthread_cancel(); If success, it returns a 0; It may return an error number if: -[ESRCH] No thread could be found corresponding to that thread ID It will not return [EINTR]