How to obtain JNIEnv pointer and jobject reference in arbitrary contexts?

Question

Hi,
I need your hand. How to obtain JNIEnv pointer and jobject reference in arbitrary contexts? (See below source codes for details)
I made some tries according to JNI spec, but still failed to get it work. Could you please provide your solutions? Better show me some source codes.
Thank you very much !!!
#include <jni.h>
#include "MessageThread.h"
#include "MyServer.h"
// this is callback function called by the native C++ library
void processEvent(int progress)
   in this function, i want to get "env", "obj" ( HOW? ),
   then i can do below to invoke Java function "updateUI":
   cls = env->GetObjectClass(obj);
   mid = env->GetMethodID(cls, "updateUI", "(I)V");
   env->CallVoidMethod(obj, mid, progress); 
JNIEXPORT void JNICALL
Java_MessageThread_handleMessageQ(JNIEnv *env, jobject obj)
  MyServer* server = MTMServer::Instance();
  if (server != NULL)
    // must register a callback function before "QueryProgress"
    server->RegisterCallback(processEvent);
    // query message within a loop, and callback "processEvent" frequently
    server->QueryProgress();
  return; 
}

Answer 1

jschell, thanks for your suggestions.
And caching the second is definitely wrong. Arguments are passed as local references. The reference lifetime is only guaranteed for the lifetime of the method call.In my case, it just works, because my "callback" is only called before the "handleMessageQ" returns, which means it's within the lifetime of "jobject", etc.
Use GetEnv to get the environment.Could you please provide some sample codes?
Create a static java method which returns the object reference. In your callback call that method to get the reference that you want to work with. I didn't really understand. Could you please show me some sample codes?
Thanks a lot!