Alert-on-update: a communication aid for shared memory multiprocessors

摘要: A traditional advantage of shared-memory multiprocessors is their ability to support very fast implicit communication: if thread A modifies location D, thread B will see the change as soon as it tries to read D; no explicit receive is required. There are times, however, when B needs to know of A’s action immediately. Event-based programs and condition synchronization are obvious examples, but there are many others. Consider a program in which B reads V from D, computes a new value V (a potentially time-consuming task), and uses compare-and-swap to install V in D only if no other thread has completed an intervening update. If some thread A has completed an update, then all of B’s work subsequent to that update will be wasted. More significantly, suppose we generalize the notion of atomic update to implement software transactional memory (STM)[4]. Now A may not only force B to back out (abort) and retry, it …