Synchronous Operations as First-Class Values

Abstract

Synchronous message passing via channels is an interprocess communication (IPC) mechanism found in several concurrent languages, such as CSP, occam, and Amber. Such languages provide a powerful selective I/O operation, which plays a vital role in managing communication with multiple processes. Because the channel IPC mechanism is “operation-oriented,” only procedural abstraction techniques can be used in structuring the communication/synchronization aspects of a system. This has the unfortunate effect of restricting the use of selective I/O, which in turn limits the communication structure. We propose a new, “value-oriented” approach to channel-based synchronization. We make synchronous operations first-class values, called events, in much the same way that functions are first-class values in functional programming languages. Our approach allows the use of data abstraction techniques for structuring IPC. We have incorporated events into PML, a concurrent functional programming language, and have implemented run-time support for them as part of the Pegasus system.