# Java volatile again

http://en.wikipedia.org/wiki/Volatile_variable

The Java programming language also has the volatile keyword, but it is used for a somewhat different purpose. When applied to a field, the Java volatile guarantees that:

(In all versions of Java) There is a global ordering on the reads and writes to a volatile variable. This implies that every thread accessing a volatile field will read its current value before continuing, instead of (potentially) using a cached value. (However, there is no guarantee about the relative ordering of volatile reads and writes with regular reads and writes, meaning that it's generally not a useful threading construct.)
(In Java 5 or later) Volatile reads and writes establish a happens-before relationship, much like acquiring and releasing a mutex.[9]

Using volatile may be faster than a lock, but it will not work in some situations.[citation needed] The range of situations in which volatile is effective was expanded in Java 5; in particular, double-checked locking now works correctly.[10]


http://en.wikipedia.org/wiki/Happened-before

In computer science, the happened-before relation (denoted: \to \;) is a relation between the result of two events, such that if one event should happen before another event, the result must reflect that.