JNI via Server-Side Language

Question

I'd like to use the following post as a reference: http://72.5.124.102/thread.jspa?threadID=788137&messageID=4479784
"The DLL will remain loaded between calls, so if you use a global variable to store the connection then it should be ok. "
Of course this makes logical sense. However, JNI doesn't have a handle from my understanding... JNI looks like this:
private native void nativeMethodInvoke();
static {
    System.load(path+dllName) // many alts to this, but yea.
// somewhere in main thread....
SelfClass varRefToSelf=new SelfClass();
// where SelfClass is the current class running.
// This doesn't make sense to me, considering usage of 'this' - so if anyone can explain that, I would greatly appreciate it.
varRefToSelf.nativeMethodInvoke();So.... am I supposed to keep a global reference within my class, to itself?!?
The actual problem is that I'm using a server-side language to invoke Java, and thus C++ via JNI. However, the server-side language is creating a new instance of the JAR upon each invocation. So my plan was to pass a reference to the module handle, and somehow manage to get that back to server-side language, and then furthermore back to Java JNI. Am thinking about moving to a servlet instead, since this doesn't appear to be possible - as unfortunate as that is.
Would SingleThreadModel work in this case? Or should I have C++ thread itself, so when Java makes a call, I can let C++ handle data by forwarding to correct module in memory? Assuming the above mentioned post is accurate, then the DLL, when loaded by Java, will stay in memory until unloaded. If the jvm is exiting after each server-side invocation, I must assume multiple instances of the dll are being created. So, am thinking this prospect will work... servlets aside...
Any help is appreciated. I clearly do not understand JNI as well as I should.
*Edit:
I have already tried this, and found that C++ DLL's thread is definitely active in memory post-jvm exit. The DLL also appears to be loaded multiple times, as the data I'm dealing with appears to be unique, in that it's not "stepping into itself" and overwriting pointers, or anything.
Am I going to have to create an instance of my class, via itself, to launch itself in the jvm manually - to keep the reference to dll in memory?
Although that statement sounds terribly redundant... I believe it's accurate...
1.) Create instance of class that's called by server-side, launch it under new jvm
2.) Have orig class return to server-side as normal, and forward any new requests to the jvm-launched "self"; based on detection of class/jvm in memory...
For being cross-platform "magical", Java sure makes it difficult to perform pretty basic tasks....

Answer 1

Thanks for the great information jschell, this clears up alot. I'll play around with these new prospects and see if I can get this running properly.
Also, let me define more what I'm actually doing.
I'm using Railo, and a CFX "tag" to invoke a JAR. This Jar contains the JNI to execute a DLL's code. This dll's code is merely in place to perform some server tasks - mostly routine file maintenance, and checks to ensure normal operation. Some of this includes db queries. Yes this can be done in Java for the most part, but we plan to use the DLL exports later in a deployment scenario.
So, "Did you mean it is loading the jar each time?", I do believe so. However, the instances appear to be different. If i were to create a thread within the JNI invoking class, which i have tried by the way, and create a global variable with some value, the second calling of the JAR file reports that it has not been defined yet on class initialization. Additionally, the thread I mentioned also halts, and does not exist within the second calling.
Let me show some actual code...
Test.cfm...
<cfx_mytag Library="myLibrary.dll" task="function1">
<cfscript>
... // do some stuff.
</cfscript>If I were to alter that to:
<cfx_mytag Library="myLibrary.dll" task="function1">
<cfx_mytag Library="myLibrary.dll" task="function2">
<cfscript>
... // do some stuff.
</cfscript>I found that function2 in the same JAR, loaded via "cfx_mytag", reports inexistance of function1's execution - which registered a value into a global var.
This is why I must assume that the JAR is being loaded independantly - each time. Correct me if wrong. Perhaps my terminology is off - the class within the jar file is multi-instanced, as far as I can tell. Or rather... Railo is creating mutliple instances of this class - and thus I lose my handle to my dll - every call... Seemingly at least.
//Java...
import com.allaire.cfx.*;
public final class myClass implements CustomTag {
     private Request req;
     private Response res;
        public boolean igetresetoften;
     private native void gogoGadgetDLL();
     public myClass() {
    public void processRequest(Request request,Response response) throws Exception {
         this.req=request;this.res=response;
          if (!this.igetresetoften) {
                 igetresetoften=true;
                 res.write("yea... this is annoying");
            // in actual code - function1() assigns global var.
            // and function2() reports to response buffer the value of the global var , which is constantly false each run.
}Notice the similarity to a servlet (request/response buffers). I've dealt with servlets, so I know that all requests are threaded.. but the global vars in a servlet are, in fact, ... global. Not in this case, it would seem.
Thanks again, I'll let you know of my results, late tonight.
Edited by: jSD7 on Nov 13, 2009 4:20 PM