Attach native thread to JVM

Question

Hi,
I use JNI to extend my Java class with some Windows specific functions.
In the native code I have to check the value of a variable from Java and for this I created a new native thread.
The documentation says that "the JNI interface pointer is valid only in current thread", so one must attach the new thread to the JVM in order to get a new interface pointer. But for attaching a thread to the JVM you need the ORIGINAL JNI INTERFACE POINTER. On the other hand, the documentation says that you "must not pass the interface pointer from one thread to another". So, I don't understand how to do it?
Here is a sample from my code:
JNIEXPORT jint JNICALL
Java_com_cts__TestJNI_startTask(JNIEnv *env, jobject obj, jstring name)
//creating a global reference
jobject globalObj = env->NewGlobalRef(obj);
//create the new thread
hThread = CreateThread(NULL,
0,
(LPTHREAD_START_ROUTINE) WaitForStop,
(LPVOID) env,//=>>> it mustn't be passed!
0,
&tid);
//the thread method, which check the value of "status" field from Java
void WINAPI WaitForStop(LPARAM lparam)
JavaVM *jvm;
JNIEnv *jenv;
pInitData->lparam->env->GetJavaVM(&jvm);
jint res = jvm->AttachCurrentThread((void**) &jenv, NULL);
if (res < 0) {
return;
jclass jclasjni = jenv->GetObjectClass(globalObj);
jfieldID jfid = jenv->GetFieldID( jclasjni, "status", "I");
jint jstatus = 0;
do
     Sleep(1000);
     jstatus = jenv->GetIntField(globalObj, jfid);
} while (jstatus == 0);
jvm->DetachCurrentThread();
Is it correct the way I attached the thread?
Because I don't quite understand this JNI interface pointer issue.
Thanks in advance

Answer 1

Ahhh - ha - got it working.
Here is how I did it:
dynamically link to the GetCreatedJavaVMs() function in the jni library (hJVM is the result of an earlier call to LoadLibrary):
     // type definitions for function addresses returned by loading jvm.dll
     typedef jint (JNICALL GetCreatedJavaVMs_t)( JavaVM**, jsize, jsize* );
     // function definitions for functions used in jvm.dll
     GetCreatedJavaVMs_t *GetCreatedJavaVMs;
     GetCreatedJavaVMs = (GetCreatedJavaVMs_t*)GetProcAddress( hJVM, "JNI_GetCreatedJavaVMs" );
     return GetCreatedJavaVMs( jvm, bufLen, nVMs);Get an appropriate instance on the JVM by called GetCreatedJavaVMs and pulling the first one. Once we have that, call AttachCurrentThread to get a JNIEnv pointer that we can use for doing work:
     JavaVM *jvm;
     JNIEnv *jenv;
     jint nSize = 1;
     jint nVms;
     jint nStatus = JAVAVM.GetCreatedJavaVMs( &jvm, nSize, &nVms );
     jint res = jvm->AttachCurrentThread((void**) &jenv, NULL);
    jclassStartup =
       jenv->FindClass(sStartupClass); // do some workWhen all done with the invocation, detach the jenv pointer from the current thread:
     jvm->DetachCurrentThread();Works like a charm.
- K