Asynchrony (due to unknown message transmission delay) complicates the design of protocols for distributed systems. To simplify the protocol design task therefore, the authors propose an interprocess (point-to-point) communication mechanism that has the characteristic of instantaneous message passing. They first establish a hierarchy among synchronization properties, which shows that to ensure the logically instantaneous message passing property it is not always necessary to use a rendezvous mechanism. Next, they propose a solution to the logically instantaneous message passing problem that is more efficient than R. Bagrodia's (1989) rendezvous and K.J. Goldman's (1991) logically synchronous multicast in the point-to-point (single-cast) setting. This algorithm has the following properties: it is applicable without deadlock to the partner model in which each process acts as both client and server; it requires three control messages to send an application message, which is shown to be quasioptimum message complexity; and its worst-case response time from a send request to the occurrence of the corresponding send event is 2k/spl Delta/ (sec.), where k is the maximum number of interfering send requests and /spl Delta/ (sec.) is an assumed upper bound on interprocess communication delay. Furthermore, two modified algorithms are proposed: one for reducing the number of control messages required for an application message, and the other for attaining a shorter average response time by using a randomization technique.>

Application systems in real-time processing fields, in addition to those systems whose most important requirement is to complete processing within a given response time, also include systems whose aims are to raise throughput within the response time restrictions, in which a high degree of multi-tasking is of primary importance. The paper makes proposals on task scheduling and OS functions in highly multi-tasking real-time processing domains, and outlines a research project presently being undertaken in NTT to study real-time OS performance evaluation methods geared to these domains.>

This paper clarifies the relation between the diameter k and the edge or node connectivity Ce or c,, of digraphs. The following two inequalities are derived: where n is the number of nodes, d is the maximum degree, and d is the minimum degree.