java.lang.UnsatisfiedLinkError: Native Library {____.dll} already loaded in another classloader

Question

I'm using a JAR file of my own, which uses a Java library (JHDF5), that in turn uses a dll through JNI. When I use my own JAR file in MATLAB, and then have to rebuild it while debugging, I get this error when I try to use it again, after calling clear java and creating a new object from my JAR file:

java.lang.UnsatisfiedLinkError: 
Native Library C:\deka\proj\java\ESPDF\dist\lib\jhdf5.dll 
already loaded in another classloader

and I can't solve it without shutting down MATLAB and reopening, which is a pain in the neck.

What is this error and whose fault is it? (mine? MATLAB's? JHDF5 for not freeing the DLL or checking to see if it's already loaded)

Answer 1

In general, there is no way for Java code to unload a native dll. http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=5075039

Given that, once a dll is loaded, it's there for the lifetime of the JVM and the VM will ensure that it is loaded once and only once.

To answer the question of blame, I suppose it's the fault of the code that attempts to load the dll without checking if its already available.