SMARTS--Shared-memory Multiprocessor Ada Run Time Supervisor

Candidate: Flynn-Hummel,Susan Frances

Abstract

The programming language Ada is primarily intended for the construction of large scale and real time systems. Although the tasking model of Ada was aimed mainly at embedded systems, its rich set of synchronization operators together with its support for programming in the large, make Ada increasingly attractive for writing inherently parallel, computationally intensive, numeric and symbolic applications. Highly parallel shared-memory MIMD machines such as the NYU Ultracomputer have traditionally been regarded as suitable for large-scale scientific code, and not for more symbolic or heterogeneous concurrent applications such as are found in Artificial Intelligence or real-time programming. However, these applications would benefit greatly from (and even require) the computational power provided by highly parallel machines. It is therefore desirable to develop Ada implementations for highly parallel machines. The concern has been that the cost of managing large numbers of Ada tasks will negate the speedup obtained from their parallel execution. Indeed, a run-time supervisor for Ada must contend with many potentially expensive serialization points, that is to say, constructs that may take time proportional to the number of tasks involved. In this thesis we show that a run-time supervisor for an implementation of Ada on highly parallel machines can be written which is free of costly serialization points. The run-time supervisor SMARTS (Shared-memory Multiprocessor Ada Run Time Supervisor) depends on the hardware synchronization primitive $fetch\&\Phi$, and supports the tasking features of Ada in a highly parallel manner. We further reduce the overhead of Ada tasking, by means of micro-tasking, i.e. the explicit scheduling of a family of Ada tasks on a specified number of processors. Thus, Ada tasks are implemented as light weight processes managed by SMARTS, rather than full blown operating systems processes. Finally, SMARTS implements Ada shared variables efficiently by means of relay sets. Relay sets not only provide a means for identifying and resolving references to shared variables, but also facilitate the implementation of the Ada rendezvous mechanism as a remote procedure call.