Netzer's research while affiliated with Brown University and other places

We address the problem of detecting race conditions in programs that use semaphores for synchronization. Netzer and Miller showed that it is NP-complete to detect race conditions in programs that use many semaphores. We show in this paper that it remains NP-complete even if only two semaphores are used in the parallel programs. For the tractable case, i.e., using only one semaphore, we give two algorithms for detecting race conditions from the trace of executing a parallel program on p processors, where n semaphore operations are executed. The first algorithm determines in O(n) time whether a race condition exists between any two given operations. The second algorithm runs in O( np log n) time and outputs a compact representation from which one can determine in O(1) time whether a race condition exists between any two given operations. The second algorithm is near-optimal in that the running time is only O( log n) times the time required simply to write down the output.

A techinque for tracing and replaying message-passing programs for debugging is presented. The technique is optimal in the common case and has good performance in the worst case. By making runtime tracing decisions, only a fraction of the total number of messages is traced, gaining two orders of magnitude reduction over traditional techniques which trace every message. Experiments indicate that only 1% of the messages often need to be traced. These traces are sufficient to provide replay, allowing an execution to be reproduced any number of times for debugging. This work is novel in that runtime decisions are used to detect and trace only those messages that introduce nondeterminacy. With the proposed strategy, large reductions in trace size allow long-running programs to be replayed that were previously unmanageable. In addition, the reduced tracing experiments alleviate tracing bottlenecks, allowing executions to be debugged with substantially lower execution-time overhead.