@VisibleForTesting
  protected void awaitIndex() {
    try {
      mCountDownLatch.await();
    } catch (InterruptedException e) {
      FLog.e(TAG, "Memory Index is not ready yet. ");
    }
  }
Blocks current thread until having finished initialization in Memory Index. Call only when you
need memory index in cold start.
imagepipeline-base/src/main/java/com/facebook/cache/disk/DiskStorageCache.java