JNI Object Lifetimes Quick Reference

table.md

JNI Object	Use across JNI calls?	Use on different thread?	Notes
JavaVM	Yes	Yes	To obtain an instance of JavaVM, either: Expose a native export jint JNI_OnLoad(JavaVM* vm, void* reserved), which will be invoked when LoadLibrary is called from Java Call pJNIEnv->GetJavaVM(&pJavaVM) on a valid JNIEnv You don't need to clean up a JavaVM.
JNIEnv	Yes	No	A JNIEnv is valid across JNI calls, but only on its original thread. If you are going to cache a JNIEnv, consider using a thread_local or similar. If a JNIEnv is not available for the current thread (e.g. within a native callback), one can be obtained by calling pJavaVM->AttachCurrentThread(&pJNIEnv, null). In this case you are responsible for cleaning up with pJavaVM->DetachCurrentThread(). Otherwise, you don't need to clean up a JNIEnv.
Primitive value types jboolean, jchar, jshort, jfloat, jdouble, jsize, jint, jlong, jbyte	Yes	Yes	These are just aliases for normal native value types, so there are no special lifetime or cleanup considerations.
Reference types jobject, jclass, jthrowable, jstring, jarray, jbooleanArray, jbyteArray, jcharArray, jshortArray, jintArray, jlongArray, jfloatArray, jdoubleArray, jobjectarray	No (local refs)	No (local refs)	If one of these is passed in as an argument to a JNI call, or returned from another JNI API, it is typically a local reference and is only valid for the duration of that JNI call, on that same thread. These do not require any cleanup. A durable global reference can be created from any local reference by calling globalJThing = (jthing) pJNIEnv->NewGlobalRef(localJThing). Global references are valid across JNI calls and on any thread. Global references must be cleaned up with pJNIEnv->DeleteGlobalRef(globalJThing).
	Yes (global refs)	Yes (global refs)
ID types jfieldID, jmethodID	Yes	Yes	These are durable and can be used without restriction. No cleanup is required.