The Stability And Latency Of Concurrent-X Exclusive-Y

We analyze the concurrent-X exclusive-Y protocol for access to a shared resource, where X and Y are atomic operations. The simplest example occurs in database and distributed operating systems, where X may represent read/query (R) operations and Y represents a write/update (W) operation or any operation which requires locked access to the resource by a single party in order to guarantee consistency. 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.