Location-Based Memory Fences

Traditional memory fences are program-based. That is, a mem-ory fence enforces a serialization point in the program instruction stream — it ensures that all memory references before the fence in the program order have taken effect before the execution contin-ues onto instructions after the fence. Such program-based memory fences always cause the processor to stall, even when the synchro-nization is unnecessary during a particular execution. We propose the concept of location-based memory fences, in which a proces-sor executing a concurrent algorithm incurs synchronization cost due to latency of memory fences only when the synchronization is needed. Unlike a program-based memory fence, a location-based mem-ory fence serializes the instruction stream of the executing thread T1 only when a different thread T2 attempts to read the memory lo