How to garbage collect a direct buffer in Java

Question

I have a memory leak that I have isolated to incorrectly disposed direct byte buffers.

ByteBuffer buff = ByteBuffer.allocateDirect(7777777);

The GC colle

Answer 1

The DBB will be deallocated once it hits the reference queue, and the finalizer is run. However, as we cannot depend on a finalizer to run, we can use reflection to manually call its "cleaner".

Using reflection:

/**
* DirectByteBuffers are garbage collected by using a phantom reference and a
* reference queue. Every once a while, the JVM checks the reference queue and
* cleans the DirectByteBuffers. However, as this doesn't happen
* immediately after discarding all references to a DirectByteBuffer, it's
* easy to OutOfMemoryError yourself using DirectByteBuffers. This function
* explicitly calls the Cleaner method of a DirectByteBuffer.
* 
* @param toBeDestroyed
*          The DirectByteBuffer that will be "cleaned". Utilizes reflection.
*          
*/
public static void destroyDirectByteBuffer(ByteBuffer toBeDestroyed)
    throws IllegalArgumentException, IllegalAccessException,
    InvocationTargetException, SecurityException, NoSuchMethodException {

  Preconditions.checkArgument(toBeDestroyed.isDirect(),
      "toBeDestroyed isn't direct!");

  Method cleanerMethod = toBeDestroyed.getClass().getMethod("cleaner");
  cleanerMethod.setAccessible(true);
  Object cleaner = cleanerMethod.invoke(toBeDestroyed);
  Method cleanMethod = cleaner.getClass().getMethod("clean");
  cleanMethod.setAccessible(true);
  cleanMethod.invoke(cleaner);

}