CS/TR-89-37.3 Multi-threaded Processes in CHORUS/MIX

Interest in concurrent programming in recent years has spurred development of ‘‘threads’’, or ‘‘lightweight processes’’, as an operating system paradigm. UNIX-based systems have been especially affected by this trend because the smallest unit of CPU scheduling in UNIX, the process, is a rich and expensive software entity with a private memory address space. In this article we examine performance constraints affecting concurrent programs, including real-time applications, in order to understand and evaluate the demand for a new scheduling model. Although performance criteria differ sharply among various application domains, we conclude that a single thread model can provide efficient concurrent execution in a general-purpose operating system. We describe the design considerations behind the thread-management facilities of CHORUS/MIX, a UNIX-compatible operating system built for distributed, real-time, and parallel computing. Mechanisms for processor scheduling and inter-thread synchronization must satisfy the needs of each of these three categories of concurrency. Extension of the traditional UNIX interface to the multi-threaded environment is an area of particular delicacy. CHORUS/MIX adopts novel approaches for signal handling and other UNIX facilities so as to ensure a smooth transition from sequential to concurrent semantics in applications