Java : Memory Consistency and Process Coordination � ( Extended

In Java, some memory updates are necessarily visible to some threads but never to others. A definition of Java memory consistency must take this fact into consideration to capture the semantics of non-terminating systems, such as a Java operating system. This paper presents a programmer-centered formal definition of Java memory behavior that captures those semantics. Our definition is employed to prove that it is impossible to provide fundamental process coordination in Java, such as critical sections and producer/consumer coordination, without the use of the / 0 / # 1 2 3 and 4 0 # 2 constructs. However, we introduce a form of synchronization that is weaker than 4 0 # 2 s and would suffice to solve some of these problems in Java. keywords: Java, Java Virtual Machine, memory consistency models, process coordination, critical section problem, producer/consumer problem, non-terminating systems.