On 1/20/11 6:02 PM, Per-Erik Svensson wrote:
Hi,
I would like to know when a class is loaded. I guess it is a bit different
depending on things like usage of static members and the like but... Say
java.util.Logger. I have a bundle that only consumes services. When the
bundle is started it is running a few background threads. When the bundle is
stopped, the background threads are cancelled. When they are cancelled, they
will post a task on the event dispatch thread (I'm using swing workers) and,
since they were cancelled, they will log just that ("Background thread
interrupted" or similar is written to log).
Now, everything worked fine up until the edt-task was about to log. At that
point, felix threw an exception. Sadly, I don't have the stack trace atm and
I'm not sure I can reproduce. I'm just curious if anyone knows what this can
be. The offending line was calling
java.util.Logger.getLogger(getClass().getName()).log(Level.INFO, "BG-thread
cancelled) //or similar
And remember that the bundle jar-file has been removed (with the help of
FileInstall) from the system. It might linger in the bundle cache (I don't
know how long it stays there) but the bundle is stopped and (presumably)
uninstalled.
I just removed the logger code to make it work. However, I'm suspecting that
the cause of the error is either
1. getClass() must have a class loader and that is gone because the
bundle is uninstalled.
If you have a thread executing on the class, then the class loader isn't
gone since the thread has a reference to the class and the class has a
reference to its class loader.
2. The static Logger isn't loaded yet or uses classes that aren't loaded
yet and thus felix informs me that it cant find the class.
Something like this could be.
So, (a) when is a class loaded, (b) is there any good "pattern" for dealing
with disposing threads in OSGi, and (c) am I completely off here? :)
For (a) it just depends. They are loaded on demand by the JVM. In some
cases loading a class will cause other class loads for dependent types
necessary for defining the class. For types used in methods, they will
be loaded on demand (although I'm not sure if this is mandated).
For (b), the best you can do is stop your threads in your activator
stop() method. Your bundle will not be uninstalled until after it
returns from its stop() method. In Felix, we don't hold locks for class
loading, so you can end up with situations were threads will have issues
loading classes from a dependent bundle, but they won't have problems
loading classes from themselves as long as they are stopped in their
activator stop() method.
-> richard
Ok, (d) would it help writing "MyClass.class.getName()"?
Regards,
Per-Erik Svensson
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