Sorry if this has been asked before. I can't seem to get to the archives.
In the source code for OJB I have noticed several uses of the Singleton
pattern. Mostly, the code is of then form,
<SingletonName> {
private static <SingletonName> _instance;
<SingletonName> getInstance() {
if(_instance == null) {
_instance = getNewInstance();
}
return _instance;
}
I am puzzled by this idiom because it has been documented as "broken" for
the Java memory model with respect to multi-thread applications.
http://www.javaworld.com/javaworld/javatips/jw-javatip67-p2.html states,
"Using lazy instantiation for a concrete Singleton is not only unnecessary
in Java, it's downright dangerous in the context of multithreaded
applications."
Ref:
http://www.javaworld.com/javaworld/javatips/jw-javatip67.html?
http://www.javaworld.com/javaworld/jw-02-2001/jw-0209-double.html
http://www.javaworld.com/javaworld/jw-05-2001/jw-0525-double.html
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