@Override
  public synchronized void onFailure(@Nullable Throwable t) {
    if (mIsFinished) {
      return;
    }
    mIsFinished = true;
    try {
      onFailureImpl(t != null ? t : new Throwable("null throwable"));
    } catch (Exception e) {
      onUnhandledException(e);
    }
  }
Creates a simple status value which only identifies whether this is the last result.
imagepipeline/src/main/java/com/facebook/imagepipeline/producers/BaseConsumer.java