Re: Intended uses of 1.5 atomics package

Thomas Hawtin <>
Tue, 08 Aug 2006 10:36:02 +0100
Christopher Benson-Manica wrote:

class foo {
  private AtomicInteger bar=new AtomicInteger();

                 (really make sure each thread see the initialiser value)

  public int getBar() {
    return bar.get();

  public void incrementBar() {

Does this example miss the real point of why the
java.util.concurrent.atomic classes exist?

The code isn't much simpler. However it may well be much faster,
particularly on a multiprocessor machine where an instance is used
frequently by multiple threads.

There is a similar example in the 1.6 (mustang) API docs for ThreadLocal
(which now even compiles).

 From 1.5, in the source of there is an example of
using AtomicLong.compareAndSet to avoid a lock (could have used
weakCompareAndSet in this particular case). In 1.5 the class as a whole
is theoretically thread unsafe as the AtomicLong is not final.

Tom Hawtin

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