Question

I’ve got an app where a thread is trying to send lots of Location objects via a Handler to the UI thread, where they get analyzed and passed on to other threads. I’ve noticed the app has a memory leak, as it eventually crashes 2-3 hours after starting up. If I use DDMS to profile the heap, I notice a gradual increase in the number of “Data Objects” (about 1500 per minute). It appears those 1500 are approximately evenly split between 16-byte and 32-byte items.

After gradually disabling parts of my app, I found that the Location generating thread’s call to the Handler appears to cause the leak.

I have gradually narrowed down the required parts of my thread to this:

class UIActivity implements Handler.Callback
{
@Override 
public void onCreate()
{
  m_handler = new Handler(this);
}

@Override
public boolean handleMessage(Message m)
{
  switch(m.what)
  { 
    case FAKE_LOCATION:
      m.obj = null; // desperate anti-leak measures
      return true;
  }
  return false;
}
public static class FakeLocationGenerator extends Thread
{
  private Handler m_callback;
  public FakeLocationGenerator(Handler callback)
  {
    m_callback = callback;
    start();
  }

  @Override
  public void run()
  {
    while(true)
    {
      Thread.sleep(50); // makes for 20hz
      Location l = new Location("fake");
      Message m = new Message();
      m.what = FAKE_LOCATION;
      m.obj = l;
      m_callback.SendMessage(m);
    }
  }
}
}

The Handler.Callback.handleMessage() implementation on the UI activity just returns true and does nothing with the message. If I comment out the m_callback.SendMessage call, then the memory leak disappears. I tried a giant hack of calling Handler.removeMessages(FAKE_LOCATION) after each FAKE_LOCATION message, but that did nothing.

Any ideas?

Answer 1

Firstly, you should be using Message.obtain() and Message.recycle().

Secondly, is it possible that maybe there is no leak and you are simply generating new messages faster than they are being processed…?