Race-condition detection in parallel computation with semaphores (extended abstract)

Abstract

We address a problem arising in debugging parallel programs, detecting race conditions in programs using semaphores for synchronization. It is NP-complete to detect race conditions in programs that use polynomial number of semaphores [10]. We show in this paper that it remains NP-complete even if the programs are allowed to use only two semaphores, which settles the open question raised in [10]. The proof uses a technique that simulates a graph with any number of semaphores by a graph with only two semaphores.

For the case of single semaphore, Lu et al. [8] give the previously only-known polynomial-time algorithm that runs in time O(n^1.5 p), where p is the number of processors and n is the total number of semaphore operations executed. Their algorithm, however, detects only a special class of race conditions. In this paper we cope with the general race-condition detection problem and give an O(np log n) -time algorithm.The output of our algorithm is a compact representation of size Θ(np), from which one can determine in constant time whether a race condition exists between two given operations. Our algorithm is near-optimal in that the time it takes is only O(log n) times the time required simply to write down the output.

The detailed version of this extended abstract can be located at the following URL: http://www.cs.brown.edu/people/hil/research/publication/mhb.ps.