#jsr133 what is java memoryModel memoryModel

• What is a memory model, anyway?
• Do other languages, like C++, have a memory model?
• What is JSR 133 about?
• What is meant by reordering?
• What was wrong with the old memory model?
• What do you mean by incorrectly synchronized?
• What does synchronization do?
• How can final fields appear to change their values?
• How do final fields work under the new JMM?
• What does volatile do?
• Does the new memory model fix the “double-checked locking” problem?
• What if I’m writing a VM?
• Why should I care?

比较有代表性的介绍 What is javaMemoryModel:

1. The Java Memory Model defines the behavior of volatile and synchronized, and, more importantly,

ensures that a correctly synchronized Java program runs correctly on all processor architectures;

1. The Java Memory Model was an ambitious undertaking;

it was the first time that a programming language specification

attempted to incorporate a memory model which could provide consistent semantics

for concurrency across a variety of architectures. Unfortunately,

defining a memory model which is both consistent and intuitive proved far more difficult than expected.

JSR 133 defines a new memory model for the Java language which fixes the flaws of the earlier memory model.

In order to do this, the semantics of final and volatile needed to change.