protected Pair<CacheKey, ImageRequest.RequestLevel> getKey(ProducerContext producerContext) {
    return Pair.create(
        mCacheKeyFactory.getEncodedCacheKey(
            producerContext.getImageRequest(), producerContext.getCallerContext()),
        producerContext.getLowestPermittedRequestLevel());
  }
Multiplex producer that uses the encoded cache key to combine requests.
imagepipeline/src/main/java/com/facebook/imagepipeline/producers/EncodedCacheKeyMultiplexProducer.java