The Use of Multithreading for Exception Handling Craig

Figure 1. Traditional vs. Multithreaded Exception Handling. Six instructions have been fetched when an exception is detected on the fourth. Traditionally (a), instructions 4-6 are squashed and must be refetched after the exception handler is fetched. With our multithreaded mechanism (b), a second thread fetches the exception handler (AD), and then the main thread continues to fetch (7,8). The exception handler is retired before the excepting instruction. (c) This makes the global retirement order different than the fetch order, but each thread retires instructions in it's fetch order.