Race-Condition Detection in Parallel Computation with Semaphores

We address a problem arising in debugging parallel programs, detecting race conditions in programs using semaphores for synchronization. It is NPcomplete to detect race conditions in programs that use many semaphores [10]. We show in this paper that it remains NP-complete even if the programs are allowed to use 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(n1:5p), 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 logn)-time algorithm. The output of our algorithm is a compact representation from which one can determine in constant time whether a race condition exists between two given operations.