AutoSynch: an automatic-signal monitor based on predicate tagging

Abstract

Most programming languages use monitors with explicit signals for synchronization in shared-memory programs. Requiring programmers to signal threads explicitly results in many concurrency bugs due to missed notifications, or notifications on wrong condition variables. In this paper, we describe an implementation of an automatic signaling monitor in Java called AutoSynch that eliminates such concurrency bugs by removing the burden of signaling from the programmer. We show that the belief that automatic signaling monitors are prohibitively expensive is wrong. For most problems, programs based on AutoSynch are almost as fast as those based on explicit signaling. For some, AutoSynch is even faster than explicit signaling because it never uses signalAll, whereas the programmers end up using signalAll with the explicit signal mechanism.