Interesting. Didn't know it was a known problem with java 1.4.
Lazy initialization was used exactly because we don't want dispatch
threads to start unless they are needed. So ... per Wikipedia article
this is a legacy JDK problem and going forward we should simply be
using "volatile" keyword, which I think we should.
Andrus
On Mar 30, 2007, at 1:10 AM, Peter Karich wrote:
Hello!
I profile my application with netbeans profiler.
And I figured out that there are 12 (!) EventManager's DispatchThreads
started.
All are in the 'waiting' state.
I have no problems with that :-)
But could it be that this code is problematic:
public static EventManager getDefaultManager() {
if (defaultManager == null) {
synchronized (EventManager.class) {
if (defaultManager == null) {
defaultManager = new EventManager(2);
}
}
}
return defaultManager;
}
See the problems with double checked locking here:
http://en.wikipedia.org/wiki/Double-checked_locking
Particularly the section:
"One of the dangers of using double-checked locking in J2SE 1.4 ..."
A simple solution can be:
private static EventManager defaultManager = new EventManager(2);
public static EventManager getDefaultManager() {
return defaultManager;
}
OR a full synchronized method.
Peter.
