On the Cost of Uniform Protocols Whose Memory Consumption Is Adaptive to Interval Contention

A distributed shared memory protocol is called memoryadaptive, if all writes to MWMR registers are ”close to the beginning of shared memory”, that is the indices of all MWMR registers processes write to when executing the protocol are functions of the contention. The notion of memory-adaptiveness captures what it means for a distributed protocol to most efficiently make use of its shared memory. We previously considered a store/release protocol where processes are required to store a value in shared MWMR memory so that it cannot be overwritten until it has been released by the process. We showed that there do not exist uniformly wait-free store/release protocols using only the basic operations read and write that are memory-adaptive to point contention. We further showed that there exists a uniformly wait-free store/release protocol using only the basic operations read, write, and read-modifywrite that is memory-adaptive to interval contention and time-adaptive to total contention. This left a significant gap which we close in this paper. We show that no uniform store/release protocol can exist that is memory adaptive to interval contention and only uses read/write (no read-modify-write) registers. We furthermore illustrate the validity and practicality of the concept of memory adaptiveness by providing a uniform, memory-adaptive to interval contention store/release protocol for Network Attached Disks.