Method for synchronizing use of dual and solo locking for two competing

Abstract

To satisfy host requests, two competing processors self-manage access to a shared resource. Each processor maintains a lock table listing that processor's access state regarding the shared resource. Each processor repeatedly sends the other processor a state announcement message representing the processor's state. These include birth cry, heartbeat, or death knell messages. Whenever certain join-entry conditions apply to a processor, the processor performs a JOIN operation to evaluate and attempt to synchronize its lock table with the other processor's lock table. If data is needed from the other processor's lock table, the processor changes its state announcement message to birth cry. If the processor successfully synchronizes its lock table with the other processor, the JOIN operation dictates DUAL mode for that processor. If the synchronization attempt fails, SOLO results. When JOIN completes, the processor operates in its chosen mode. In DUAL, the processor's state announcement message is heartbeat, signifying healthy operation. In DUAL, the processors cooperatively establish temporary single-processor locks on the shared resource to satisfy host requests. In SOLO, a processor sets its state announcement message to death knell, advising the other processor not to access the shared resource. Also in SOLO, the processor attempts to 'acquire' the shared resource by storing a predetermined identifier thereon. In SOLO, a processor refrains from accessing the shared resource unless it has acquired it.