HELP!!! URGENT!!!How do I make JNIEnv and jobject global
Hi!
My JNI code uses a library made by another company. The mentioned library accepts requests but does not return the result/answer of requests in the usual way as return result. Instead, it calls my JNI callback method. The problem here is that my JNI callBack method in turn needs to call my java callback. Since the JNI callback function does not have the JNIEnv and jobject sent by java, it can not call the method callback in java since for it to do that, it has to have JNIEnv and jobject. I tried to declare global JNIEnv and global jobject in this manner:
JNIEnv *envGlobal;
static jobject savedReference;
In the native methods where I accepted JNIEnv as arguments, I assigned the the envGlobal this way:
envGlobal = (JNIEnv*) malloc(sizeof(JNIEnv));
envGlobal = env; // where env is an argument of type JNIEnv of some native method
I also assigned the savedReference variable as
savedReference = env->NewGlobalRef(thisObject); // I got this declaration from the Essential JNI book by Rob Gordon
but it resulted to : "request for member 'NewGlobalRef' to something not a structure or a union"
I really need to know how to do this. I need the JNIEnv and jobject references to connect back to my callBack method in java. Please, please, please help me. I will really appreciate any help. Thanks :-)
Monette
[1412 byte] By [
mon03] at [2007-9-26 8:16:01]
If I undertand your process flow correctly, it is
java program -> your dll
your dll -> other library
other library -> call back routine.
And eventually, this all unwinds.
So what you want is for the callback routine to be able to access the java environment, and the java object which has the native method.
If I have this right, then all you should have to do is the following:
1. In a global space - that is, outside any of the routines declare
JNIEnv * envGlobal;
jobject savedReference;
2. In your native method do the following:
envGlobal = env// The env passed in.
savedReference = obj// The object reference passed in.
3. Go ahead and use these in your callback.
You don't have to malloc space for the environment, and you don't need a new global reference.
Limitation:
If, in the overall processing scheme, the foreign library spawns a thread and lets your native method return immediately, then what I have just shown you won't work, and franly I don't know what WILL work. The JNI is real touchy.
Hi,
the solution is described in "The Java Native Interface" by Sheng Liang (Addison Wesley).
In short:
During loading a JNI lib the JNI_Onload function is called.
The JVM attached to the library is passed to JNI_Onload
and can be cached in a static variable of the lib.
Everytime you need the JNIEnv in a callback, you need
to inquire it with (*cached_jvm)->GetEnv( ... ) since
it might change.
Have fun,
Klaus
Arise, zombie thread! ARISE!
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