Adding env.DeleteGlobalRefCache method to avoid memory leak after env…

… instance gets out of scope

jnigi.go

@@ -224,10 +224,7 @@ func (j *JVM) AttachCurrentThread() *Env {
 
 // DetachCurrentThread calls JNI DetachCurrentThread, pass Env returned from AttachCurrentThread for current thread.
 func (j *JVM) DetachCurrentThread(env *Env) error {
-	//free cache
-	for _, v := range env.classCache {
-		deleteGlobalRef(env.jniEnv, jobject(v))
-	}
+	env.DeleteGlobalRefCache()
 
 	if detachCurrentThread(j.javaVM) < 0 {
 		return errors.New("JNIGI: detachCurrentThread error")
@@ -1909,6 +1906,15 @@ func (j *Env) GetUTF8String() *ObjectRef {
 	return utf8
 }
 
+// DeleteGlobalRefCache deletes all globalRef that are in classCache. This methods should
+// be called when an instance of *Env gets out of scope
+func (j *Env) DeleteGlobalRefCache() {
+	for _, v := range j.classCache {
+		deleteGlobalRef(j.jniEnv, jobject(v))
+	}
+	j.classCache = make(map[string]jclass)
+}
+
 // StackTraceElement is a struct holding the contents of java.lang.StackTraceElement
 // for use in a ThrowableError.
 type StackTraceElement struct {

jnigi_test.go

@@ -35,6 +35,7 @@ func TestAll(t *testing.T) {
 	PTestCast(t)
 	PTestNonVirtual(t)
 	PTestRegisterNative(t)
+	PTestDeleteGlobalRefCache(t)
 	PTestDestroy(t)
 }
 
@@ -378,6 +379,7 @@ func PTestGetJVM(t *testing.T) {
 }
 
 func PTestDestroy(t *testing.T) {
+	env.DeleteGlobalRefCache()
 	err := jvm.Destroy()
 	if err != nil {
 		t.Fatalf("DestroyJVM failed %s", err)
@@ -595,6 +597,24 @@ func PTestRegisterNative(t *testing.T) {
 	}
 }
 
+func PTestDeleteGlobalRefCache(t *testing.T) {
+	str, err := env.NewObject("java/lang/String", []byte("hello world"))
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer env.DeleteLocalRef(str)
+	var goBytes []byte
+	if err := str.CallMethod(env, "getBytes", &goBytes); err != nil {
+		t.Fatal(err)
+	}
+
+	env.DeleteGlobalRefCache()
+
+	if !assert.Empty(t, env.classCache) {
+		t.Fail()
+	}
+}
+
 func toGoStr(t *testing.T, o *ObjectRef) string {
 	var goBytes []byte
 	if err := o.CallMethod(env, "getBytes", &goBytes); err != nil {

jnigi_test_c_callback.go

@@ -17,6 +17,7 @@ import "C"
 //export go_callback_Greet
 func go_callback_Greet(jenv unsafe.Pointer, jobj uintptr, arg_0 uintptr) uintptr {
 	env := WrapEnv(jenv)
+	defer env.DeleteGlobalRefCache()
 	env.ExceptionHandler = ThrowableToStringExceptionHandler
 
 	strArgRef := WrapJObject(arg_0, "java/lang/String", false)