AutoSynch: An Automatic-Signal Monitor Based on Predicate Tagging

TL;DR

AutoSynch introduces an automatic signaling monitor in Java that eliminates concurrency bugs caused by manual signaling, achieving comparable or better efficiency than explicit signaling methods through innovative techniques like globalization, relay invariance, and predicate tagging.

Contribution

AutoSynch presents a novel automatic signaling monitor that simplifies concurrent programming and improves efficiency by removing the need for explicit signaling, using new techniques like globalization and predicate tagging.

Findings

AutoSynch is nearly as fast as explicit signaling monitors.

AutoSynch outperforms explicit signaling in some cases by avoiding signalAll.

AutoSynch effectively handles common synchronization problems like producer-consumer and dining philosophers.

Abstract

Most programming languages use monitors with explicit signals for synchronization in shared-memory programs. Requiring program- mers 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 au- tomatic 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. AutoSynch achieves efficiency in synchronization based on three novel ideas. We introduce an operation called globalization that enables the predicate evaluation in every thread, thereby reducing context switches during the execution of the program. Secondly, AutoSynch avoids signalAll by using a property called relay invari- ance that guarantees that whenever possible there is always at least one thread whose condition is true which has been signaled. Finally, AutoSynch uses a technique called predicate tagging to efficiently determine a thread that should be signaled. To evaluate the effi- ciency of AutoSynch, we have implemented many different well- known synchronization problems such as the producers/consumers problem, the readers/writers problems, and the dining philosophers problem. The results show that AutoSynch is almost as efficient as the explicit-signal monitor and even more efficient for some cases.