A methodology for implementing highly concurrent data structures

Abstract

A concurrent object is a data structure shared by concurrent processes. Conventional techniques for implementing concurrent objects typically rely on critical sections: ensuring that only one process at a time can operate on the object. Nevertheless, critical sections are poorly suited for asynchronous systems: if one process is halted or delayed in a critical section, other, non-faulty processes will be unable to progress. By contrast, a concurrent object implementation is non-blocking if it always guarantees that some process will complete an operation in a finite number of steps, and it is wait-free if it guarantees that each process will complete an operation in a finite number of steps. This paper proposes a new methodology for constructing non-blocking and wait-free implementations of concurrent objects. The object's representation and operations are written as stylized sequential programs, with no explicit synchronization. Each sequential operation is automatically transformed into a non-blocking or wait-free operation using novel synchronization and memory management algorithms. These algorithms are presented for a multiple instruction/multiple data (MIMD) architecture in which n processes communicate by applying read, write, and compare&swa, p operations to a shared memory.