The sentry system

Abstract

A system that observes the execution of each loop in any given sequential program and issues a warning if some loop execution does not terminate as expected (due to a programming error or a failure) is proposed. At each iteration of a loop execution, the program writes the current values of some variables into shared storage; these values are read later by another program called the sentry. The sentry uses these values to compute the loop's termination function at the current iteration, and issues a warning if successive values of the termination function are not monotonically decreasing. The shared storage between the program and the sentry is finite, the program never waits for the sentry during execution, and some form of mutual exclusion is achieved between the program and the sentry. Extensions of the system and an implementation of a prototype are described. >