Asynchronous communication between threads

In programming there is sometimes a need to make computation interruptible by external events. This paper argues that a dedicated language mechanism solves this need better than a pure library convention. The main issue in designing such a mechanism is specifying points of computation where it’s safe to interrupt a thread in order to execute a signal handler. The paper proposes rules for identifying such points, rules which are especially suited for impure functional languages. The proposed mechanism of asynchronous signals happens to be useful for specifying how threads should interact with Unix fork().