A microprocessor system (1) includes a host processor (2), a graphics processing unit (GPU) (3) that includes a number of processing cores (4), and an exception handler. When a thread that is executing on a processing core (4) encounters an exception in its instruction sequence, the thread is redirected to the exception handler. However, the exception event is also communicated to a task manager (5) of the GPU 3. The task manager (5) then broadcasts a cause exception message to each processing core (4). Each processing core then identifies the threads that it is currently executing that the cause exception message relates to, and redirects those threads to the exception handler. In this way, an exception caused by a single thread is broadcast to all threads within a task.