JNI Function Interception Documentation Correct?
I'm looking at the doc located here:
http://java.sun.com/javase/6/docs/platform/jvmti/jvmti.html#jniIntercept
The code sample is also a part of the Java 5 JVMTI doc. Is this code correct? It won't compile the way it is, even when the obvious ommissions are coded back in.
//JNIEnv originalJniFunctions;
//JNIEnv redirectedJniFunctions;
jniNativeInterface* originalJniFunctions;
jniNativeInterface* redirectedJniFunctions;
int globalRefCount = 0;
jobject JNICALL MyNewGlobalRef(JNIEnv *jni_env, jobject lobj){
++globalRefCount;
return originalJniFunctions->NewGlobalRef(jni_env, lobj);
}
staticvoid JNICALL vm_init(jvmtiEnv *jvmti, JNIEnv *env, jthread thread)
{
jvmtiError err;
jintruntime_version;
/* The exact JVMTI version doesn't have to match, however this
* code demonstrates how you can check that the JVMTI version seen
* in the jvmti.h include file matches that being supplied at runtime
* by the VM.
*/
err = (*jvmti)->GetVersionNumber(jvmti, &runtime_version);
if (err != JVMTI_ERROR_NONE){
fprintf(stderr,"ERROR: GetVersionNumber failed, err=%d\n", err);
exit(1);
}else{
version_check(JVMTI_VERSION, runtime_version);
}
err = JVMTI_ERROR_NONE;
err = (*jvmti)->GetJNIFunctionTable(jvmti, &originalJniFunctions);
if (err != JVMTI_ERROR_NONE){
printf("Couldn't get function table\n, error=%d\n", err);
}
err = (*jvmti)->GetJNIFunctionTable(jvmti, &redirectedJniFunctions);
if (err != JVMTI_ERROR_NONE){
printf("Couldn't get function table\n, error=%d\n", err);
}
redirectedJniFunctions->NewGlobalRef = MyNewGlobalRef;
err = (*jvmti)->SetJNIFunctionTable(jvmti, redirectedJniFunctions);
if (err != JVMTI_ERROR_NONE){
printf("Couldn't set function table\n, error=%d\n", err);
}
}
Notice I needed to comment out the JNIEnv function table types. They generate compile errors because when trying to install the MyNewGlobalRef funtion the L value is constant. Once modified to be of type jniNativeInterface* the source compiles. The function is interecepted during runtime but inside the MyNewGlobalRef call, the call to the original NewGlobalRef does not work. I have not been able to get the error because of the environment I am running in. I did use printf's to see that the nothing happend beyond the globalRef call.
I know more info may be required but I'd first like to ask if my code above is even close to being correct. I was quite confused by the example code in the JVMTI api so I know a coding error on my part is highly likely.
Thanks!
