Requirements for Programming Language Memory Models

One of the goals of the designers of the Java programming language was that multithreaded programs written in Java would have consistent and well-defined behavior. This would allow Java programmers to understand how their programs might behave; it would also allow Java platform architects to develop their platforms in a flexible and efficient way, while still ensuring that Java programs ran on them correctly. Unfortunately, Java’s original memory model, which described the way in which Java threads interact through memory, was not defined in a way that allowed programmers and architects to understand the requirements for a Java system. As part of Java Specification Request (JSR) 133 [7], a new memory model has been defined for Java. This paper outlines how the requirements for a new memory model were established, and what those requirements are. It does not outline the model itself; it merely provides a rationale.