DEBUGGING CONCURRENT ADA PROGRAMS BY DETERMINISTIC EXECUTION

An execution of a concurrent program P with input X nondeterministically exercises a sequence of synchronization events, called a synchronization sequence (or SYN-sequence). Thus, multiple executions of P with the same input X may exercise different SYN-sequences and produce different results. When debugging an erroneous execution of P with input X, it is often necessary to repeat this execution in order to collect more debugging information. However, there is no guarantee that this execution will be repeated by executing P with input X. To solve this problem requires deterministic execution debugging, which is to force a deterministic execution of a concurrent program according to the SYN-sequence of a previous execution of this program. In this paper, we present a language-based approach to deterministic execution debugging of concurrent Ada programs. Our approach is to define SYN-sequences of a concurrent Ada program in terms of Ada language constructs and to replay such SYN-sequences without the need of system-dependent debugging tools. We first show how to define a SYN-sequence of a concurrent Ada program in order to provide sufficient information for deterministic execution. Then we show how to transform a concurrent Ada program P so that the SYN-sequences of previous executions of P can be replayed. This transformation adds an Ada task to P that controls program execution by synchronizing with the original tasks in P. We also briefly describe the implementation of tools supporting deterministic execution debugging of concurrent Ada programs.