Looking more into this, it looks like there is some legacy code that
results in so many dispatch queue threads being instantiated:
* map package uses static default EM (2 threads)
* each Configuration instance uses its own EM (+5 threads per
Configuration)
Some cleanup is due here. The first case is really legacy stuff used
by the Modeler. No need to carry it over in runtime. The second case
can be improved. First CAY-610 needs to be fixed [1], second, we may
implement a smarter dispatch thread pooling, shutting down unused
threads.
To summarize, there is nothing critically broken in the current
implementation, but cleaning it up is desirable at some point. BTW, I
changed shared EM instance to be 'volatile', but I don't think it
caused us any grief to date.
Andrus
[1] https://issues.apache.org/cayenne/browse/CAY-610
On Mar 30, 2007, at 4:40 PM, Andrus Adamchik wrote:
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.
