The implication that the example singleton class causes a memory leak just
because "...it creates a hard reference to a class instance into the class
itself" is hard to believe. There are plenty of other ways to pin classes
loaded by the web app's class loader, but the singleton pattern isn't one
of them.
One common way to pin classes is through the JavaBeans Introspector. Since
the Introspector caches information about the classes it processes, those
references will keep the web app's class loader from becoming eligible for
collection. If you're using a container that doesn't take this into
account, the common solution is to create a ServletContextListener that
calls Introspector.flushCaches in its contextDestroyed method.
If your singleton is really causing a performance issue, there's probably
something else going on. If it's released open source, you might want to
post a link to the code so someone can take a look at it.
Luca Passani wrote:
Tarek Nabil wrote:
Thanks a lot Luca for pointing this out. I must say it's completely new
information to me. I wonder if it's really accurate and relevant to all
containers.
For example, in Oracle Containers for Java (OC4J), when you redeploy an
application, the OC4J instance is restarted. You can reload an
application without restarting the OC4J instance. Do you think that
would make it immune against this kind of problem? I'm also going to the
Oracle forums with that question.
can you post (or send me off-line) a pointer to your post on the Oracle
forum?
I am interested in this for a bit of open source that I have released
and where I have used a Singleton.
If I restart the application, it takes increasingly more time for the
app-server to recover each time the Singleton is rebuilt.
This is a problem I want to fix for the first release.
Luca
--
Kris Schneider <mailto:[EMAIL PROTECTED]>
D.O.Tech <http://www.dotech.com/>
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