Is it necessary to wait for rendering thread to terminate in surfaceDestroyed(...)

Question

I just wrote a simple Android app that uses SurfaceHolder.Callback interface to communicate the state of the SurfaceView. In the Callback.surfaceDestroyed() method i just informed the rendering thread to terminate and returned, like so:

    public void surfaceDestroyed(SurfaceHolder holder) {
    renderingThread.requestStop();  
    }

I did this because in the Android documentation SurfaceHolder.lockCanvas() it states that a null will be returned when the surface is not available. And also that the SurfaceHolder holds a lock internally until SufraceHolder.unloackCanvasAndPost() is called, which prevents calls to SurfaceHolder.Callback methods.

So to me it seems that it's not necessary to wait for the rendering thread to finish. However all examples I've seen wait for the thread to finish, usually something like:

    public void surfaceDestroyed(SurfaceHolder holder) {
       boolean retry = true;
       rederingThread.setRunning(false);
       while (retry) {
          try {
            thread.join();
            retry = false;
          } catch (InterruptedException e) {
        }
     }
  }

Is this really necessary? My application runs without problems.

Answer 1

One reason to follow what most of the examples do is because just because the current implementations allow for this usage, it doesn't mean future implementations will. It's better to code defensively and to what the API is documented to do rather than what a particular implementation does.

In this case, you already have working code that's been implemented the correct way. Just toss it in your code and then you don't have to worry about it again.

Answer 2

I believe for the most part it is just good practice. Imagine if it was a thread that did a lot of heavy IO. If you simply killed the thread, you could potentially cause data corruption if it was in the middle of writing to disk. Now for a rendering thread, I'm not sure what the consequences would be. Memory leaks? It really just depends on what all is happening in your rendering thread.

Answer 3

I'm not sure that your code needs to wait the end of renderingThread but it is a generic approach or a Best Practise.

I use renderingThread.requestStop() too without problems.