private static boolean isTaskCancelled(Task<?> task) {
    return task.isCancelled()
        || (task.isFaulted() && task.getError() instanceof CancellationException);
  }
Partial disk cache producer.

<p>This producer looks in the disk cache to see if it holds part of the requested image. If the
image is found, then it is passed to the consumer as a non-final result, but an adjusted request
is still sent further along to request the remainder of the image.

<p>When the final result comes from the input producer, the two parts are stitched back together
and returned as a whole.
imagepipeline/src/main/java/com/facebook/imagepipeline/producers/PartialDiskCacheProducer.java