code: public void unfinalizeBlock(int namespaceId, Block b) throws IOException {
      lock.writeLock().lock();
      try {
        // remove the block from in-memory data structure
        ActiveFile activefile = volumeMap.removeOngoingCreates(namespaceId, b);
        if (activefile == null) {
          return;
        }
        volumeMap.remove(namespaceId, b);
        
        // delete the on-disk temp file
        File metaFile = null;
        if (!activefile.isInlineChecksum()) {
          metaFile = BlockWithChecksumFileWriter.getMetaFile(
              activefile.getDataFileToRead(), b);
        }
        if (delBlockFromDisk(activefile.getDataFileToRead(), metaFile, b)) {
          DataNode.LOG.warn("Block " + b + " unfinalized and removed. " );
        }
      } finally {
        lock.writeLock().unlock();
      }
    }
docs: Remove the temporary block file (if any)