Calling into a saved java object via JNI from a different thread
- by Drake Amara
I have a java object which calls into a C++ shared object via JNI. In C++, I am saving a reference to the JNIEnv and jObject.
JavaVM * jvm;
JNIEnv * myEnv;
jobject myobj;
JNIEXPORT void JNICALL Java_org_api_init
(JNIEnv *env, jobject jObj) {
myEnv = env;
myobj = jObj;
}
I also have a GLSurface renderer and it eventually calls the C++ shared object mentioned above on a different thread, the GLThread. I am then trying to call back into my original Java object using the jobject I saved initially, but I think because I am on the GLThread, I get the following error.
W/dalvikvm(16101): JNI WARNING: 0x41ded218 is not a valid JNI reference
I/dalvikvm(16101): "GLThread 981" prio=5 tid=15 RUNNABLE
I/dalvikvm(16101): | group="main" sCount=0 dsCount=0 obj=0x41d6e220 self=0x5cb11078
I/dalvikvm(16101): | sysTid=16133 nice=0 sched=0/0 cgrp=apps handle=1555429136
I/dalvikvm(16101): | schedstat=( 0 0 0 ) utm=42 stm=32 core=1
The code calling back into Java :
void setData()
{
jvm->AttachCurrentThread(&myEnv, 0);
jclass javaClass = myEnv->FindClass("com/myapp/myClass");
if(javaClass == NULL){
LOGD("ERROR - cant find class");
}
jmethodID method = myEnv->GetMethodID(javaClass, "updateDataModel", "()V");
if(method == NULL){
LOGD("ERROR - cant access method");
}
// this works, but its a new java object
//jobject myobj2 = myEnv->NewObject(javaClass, method);
//this is where the crash occurs
myEnv->CallVoidMethod(myobj, method, NULL);
}
If instead I create a new jObject using env-NewObject, I can succuessfully call back into Java, but it is a new object and I dont want that. I need to get back to my original Java Object.
Is it a matter of switching threads before I call back into Java? If so, how do I do so ?
