A system and method for using a handler to detect asynchronous lock line reservation lost events, and switching tasks based upon whether a condition is true or a mutex lock is acquired is presented. A synergistic processing unit (SPU) invokes a first thread and, during execution, the first thread requests external data that is shared with other threads or processors in the system. This shared data may be protected with a mutex lock or other shared memory synchronization constructs. When requested data is not available, the SPU switches to a second thread and monitors lock line reservation lost events in order to check when the data is available. When the data is available, the SPU switches back to the first thread and processes the first thread's request.