A generalized message-passing mechanism for communicating sequential processes

Bidirectional message-passing (bi-io), a novel symmetric communication mechanism for concurrent processes, is introduced and developed. The mechanism is symmetric in the sense that, in one atomic action, a message is transmitted in each direction between two processes. For some applications (tree structure, systolic arrays) this method is shown to have several advantages over conventional synchronization and communication primitives (mainly conciseness of programs, absence of certain types of deadlock). The mechanism is rigorously defined with a CSP-like syntax and a weakest-precondition semantics. Two systolic arrays are developed using bidirectional message-passing: a matrix-vector multiplier and a palindrome recognizer