Performance Analysis of Concurrent-Read Exclusive-Write.

We analyze the concurrent-read exclusive-write protocol for access to a shared resource, such as occurs in database and distributed operating systems. Readers arrive according to a Poisson process and acquire shareable i.e., non-exclusive, locks which, once granted, are released after a generally distributed random period. Writers arrive according to an arbitrary renewal process and acquire exclusive locks which, once granted, are held for a random time which is also generally distributed. Locks are granted in the order in which requests are received.We derive necessary and sufficient conditions under which the queue is stable i.e., the Iatencies for reader/writer lock acquisition have a limiting distribution. In the unstable case, the delays of successive readers/writers become unbounded. The stability condition is sensitive to the interarrival-time distribution of the writers and the lock holding-time distribution of the readers but depends only on the mean lock holding-time of the writers.Distributional and moment bounds are given for the latencies of read/write requests.