.dll already loaded in another classloader?

Question

I have a webapp running under Tomcat 3.2.1 that needs to make JNI calls in order to access data and methods in legacy C++ code. A servlet is loaded on startup of the webapp that, as part of its init method, causes a data set specific to that webapp instance to be loaded into the C++ data structures.

This Java code for this servlet contains the following:

static
{
    try {
        System.loadLibrary("JCoreImpl");
        System.out.println("JCoreImpl loaded");
        m_bLibraryLoaded = true;
    } catch (UnsatisfiedLinkError e) {
        m_bLibraryLoaded = false;
        System.out.println("JCoreImpl NOT loaded " + e);
    }
}

Things work fine if there is only one webapp (let's call it "webapps/aaa").

If I have a second webapp ("webapps/bbb") that is identical to webapps/aaa except for the data set used in the C++ data structures, then webapps/aaa starts up just fine, but when webapps/bbb is started I get an error stating that:

JCoreImpl NOT loaded java.lang.UnsatisfiedLinkError: Native Library
E:\WebStation\binDebug\JCoreImpl.dll already loaded in another classloader

I need to have a separate instance of the native library for each of my webapps as each instance needs to contain data that is unique to that particular webapp. I have searched through the mail archives and read emails by Craig McLanahan explaining the classloader hierarchy. But I have not been able to find anything specific to loading a unique instance of a native library for each webapp.

Answer 1

You can't load the same native library twice.

Put the class in a jar file under <tomcat>/lib/, it will be shared over all wars.