Notes and Further Reading

Synchronous communication was introduced by C.A.R. Hoare (1978) in his paper on communicating sequential processes. The ideas in this paper led both to the CSP formalism (Hoare, 1985) and to the OCCAM programming language (INMOS Ltd., 1988a) designed by David May. OCCAM was used to program the Transputer (INMOS Ltd., 1988b), which supported both intra- and inter-processor synchronous communication in hardware.

Asynchronous message passing originated in operating systems in the late 1960s. Brinch-Hansen (1970) describes a set of message-passing primitives for the Danish RC4000 computer. Bob Balzer (1971) introduced the notion of a communication port. Asynchronous message-passing operations can now be found in all operating systems which allow processes to communicate with other machines on a network. For example, UNIX provides a port-like abstraction called a socket and a variety of calls for sending and receiving messages. Asynchronous message passing has been included in a number of experimental programming languages and in the telecommunications language CHILL (CCITT, 1993). However, neither synchronous nor asynchronous message-passing primitives have found their way into a widely accepted general-purpose programming language. Consequently, message passing in concurrent programs remains at the level of operating system calls.

The name “rendezvous” is primarily associated with the Ada programming language (Department of Defense, 1983). We have described only the basic Ada rendezvous scheme in this chapter and omitted details concerned with timeouts on calls and accepts, conditional call and conditional accept, terminate alternative in a select, and so on. These additions make the semantics of Ada inter-process communication quite complex. In particular, they make extending the Ada rendezvous from a local interaction mechanism to a remote interaction mechanism difficult. The use of rendezvous-style communication is, of course, not restricted to Ada. Many operating system message-passing primitives support request – reply message passing reasonably directly. For example, recvfrom() on a UNIX datagram socket returns an address which can be used to send a reply message. In conclusion, the use of request – reply message protocols for client – server interaction is pervasive.

In his book, Vijay Garg (2004) provides further information on message passing and implementation of a number of distributed algorithms in Java.