How to free memory allocated by native method on Java side?

Question

I am trying to pass a byte array (with random data) from native to Java and I am not sure if this causes any memory leak or not. Here's the C++ code.

JNIEXPORT jbyteArray JNICALL Java_com_sample_test_jni_TestJNI_return_1byte_1array
(JNIEnv *env, jobject obj) {
  unsigned char *byteArray = new unsigned char[LENGTH];
  srand(12345);
  for(int i = 0;i < LENGTH;i++) {
    byteArray[i] = rand() % 64;
  }
  jbyteArray data = (env)->NewByteArray(LENGTH);
  env->SetByteArrayRegion(data, 0, LENGTH, (jbyte*)byteArray);
  delete(byteArray);
  return data;
}

And here's the Java code.

class TestJNI {
  static {
    System.loadLibrary("foobar");
  }
  public native byte[] return_byte_array();
  public static void main(String[] args) {
    byte[] data = new TestJNI().return_byte_array();
    System.out.println("Data length " + data.length);
  }
}

My doubt is whether the jbytearray allocated in native code will be garbage-collected by Java. I cannot free it in native side.

Also, are there good docs which describe JNI memory management with examples?

Answer 1

The Java GC should clean up any objects you allocate.

See this answer for more details.