Release consistency

Release consistency is one of the synchronization-based consistency models used in concurrent programming (e.g. in distributed shared memory, distributed transactions etc.). Release consistency is one of the synchronization-based consistency models used in concurrent programming (e.g. in distributed shared memory, distributed transactions etc.). In modern parallel computing systems, memory consistency must be maintained to avoid undesirable outcomes. Strict consistency models like sequential consistency are intuitively composed but can be quite restrictive in terms of performance as they would disable instruction level parallelism which is widely applied in sequential programming. To achieve better performance, some relaxed models are explored and release consistency is an aggressive relaxing attempt. Sequential consistency can be achieved simply by hardware implementation, while release consistency is also based on an observation that most of the parallel programs are properly synchronized. In programming level, synchronization is applied to clearly schedule a certain memory access in one thread to occur after another. When a synchronized variable is accessed, hardware would make sure that all writes local to a processor have been propagated to all other processors and all writes from other processors are seen and gathered. In release consistency model, the action of entering and leaving a critical section are classified as acquire and release and for either case, explicit code should be put in the program showing when to do these operations. In general, a distributed shared memory is release consistent if it obeys the following rules: