Automatic-Signal Monitors with Multi-object Synchronization

Abstract

Current monitor based systems have some disadvantages for multi-object operations. They require the programmers to (1) manually determine the order of locking operations, (2) manually determine the points of execution where threads should signal other threads, (3) use global locks or perform busy waiting for operations that depend upon a condition that spans multiple objects. Transactional memory systems eliminate the need for explicit locks, but do not support conditional synchronization. They also require the ability to rollback transactions. In this paper, we propose new monitor based methods that provide automatic signaling for global conditions that span multiple objects. Our system provides automatic notification for global conditions. Assuming that the global condition is a Boolean expression of local predicates, our method allows efficient monitoring of the conditions without any need for global locks. Furthermore, our system solves the monitor composition problem without requiring global locks. We have implemented our constructs on top of Java and have evaluated their overhead. Our results show that on most of the test cases, not only our code is simpler but also faster than Java's reentrant- lock as well as the Deuce transactional memory system.