Concurrent runtime checking of annotated Ada programs

Abstract

Anna is a language for writing machine-processable annotations of Ada programs. One of the main applications of Anna is the runtime checking of an Ada program for consistency with its formal specifications written in Anna. On single-processor systems, Anna runtime checks are used during testing and debugging of software.

This paper describes strategies for distributing Anna runtime checks so that they are executed in parallel with the Ada program. Concurrent checking of an annotated program can offer a substantial computational speedup over a sequentially checked version of the same program. Concurrent checking of Anna is therefore a crucial step in producing a self-checking program by allowing runtime checks for annotations to reside permanently in production versions of the program. Parallel checking will not always be useful in self-checking code, but certain kinds of annotations require parallel checking in real-time and interactive programs.

This paper defines an efficient parallel checking model in which checking is performed by Ada tasks running in parallel with the underlying Ada program being checked. The difficulties in reporting Anna consistency violations in a parallel environment are also described. Finally, the paper discusses some of the practical aspects of mixing checking strategies whereby sequential checking may be applied to some kinds of annotations and distributed checking to other kinds.

This research was supported by the Defense Advanced Research Projects Agency under contract N00039-84-C-0211, and by the National Aeronautics and Space Administration under Grant NAGW-419.