Timestamps for programs using messages and shared variables

Algorithms for vector timestamps have been developed to determine the "happened before" relations between events of an execution of a message passing program. Many message passing programs contain variables shared by multiple processes (including threads). Such programs need to have vector timestamps for send, receive, read and write events. We define two "happened-before" relations, called strong happened-before (SHB) and weak happened-before (WHB), between events of an execution involving send, receive, read and write statements. We then present two timestamp assignment algorithms, one for SHB and the other for WHB, and show how to use such timestamps to determine the SHB or WHB relation between any two events of an execution involving send, receive, read and write statements. For a program containing n processes, the size of a vector timestamp for SHB or WHB is n, regardless of the number of shared variables in the program. Finally, we show how to apply WHB timestamps to perform race analysis for programs using messages and shared variables.