File remove(long sizeInBytes) {
      File reserveFile = null;
      removeLock.lock();
      Queue<File> reserveFilesForSize = internalMap.get(sizeInBytes);
      if (reserveFilesForSize != null && reserveFilesForSize.size() != 0) {
        reserveFile = reserveFilesForSize.poll();
      }
      removeLock.unlock();
      return reserveFile;
    }
Remove and return a file of the specified size from the reserve file map.
@param sizeInBytes the size of the file to look for.
@return the {@link File}, or {@code null} if no file exists in the map for the specified size.
ambry-store/src/main/java/com/github/ambry/store/DiskSpaceAllocator.java