The problem is GOLThread is calling SurfaceHolder.lockCanvas()
and getting null as a result too often.
From the docs on SurfaceHolder.lockCanvas()
If you call this repeatedly when the Surface is not ready (before Callback.surfaceCreated or after Callback.surfaceDestroyed), your calls will be throttled to a slow rate in order to avoid consuming CPU.
So the OS was throttling calls by putting my threads to sleep.
I fixed it by updating the code in GOLThread.run()
to have
Canvas c = null;
try {
c = mSurfaceHolder.lockCanvas();
if (c == null) {
// Pause here so that our calls do not get throttled by the
// OS for calling lockCanvas too often.
pause();
} else {
synchronized (GOLLock) {
if (gameOfLife != null) {
gameOfLife.drawAndUpdate(c);
} else {
pause();
}
}
}
} finally {
// do this in a finally so that if an exception is thrown
// during the above, we don't leave the Surface in an
// inconsistent state
if (c != null) {
mSurfaceHolder.unlockCanvasAndPost(c);
}
}