public synchronized int getInUseCount() {
    return mCachedEntries.getCount()
        - mLeastFrequentlyUsedExclusiveEntries.getCount()
        - mMostFrequentlyUsedExclusiveEntries.getCount();
  }
Gets the number of the cached items that are used by at least one client.
imagepipeline-base/src/main/java/com/facebook/imagepipeline/cache/AbstractAdaptiveCountingMemoryCache.java