code: void addToInvalidatesNoLog(Block b, DatanodeInfo n, boolean ackRequired) {
      // We are the standby avatar and we don't want to add blocks to the
      // invalidates list.
      if (this.getNameNode().shouldRetryAbsentBlocks()) {
        return;
      }
  
      LightWeightHashSet<Block> invalidateSet = recentInvalidateSets.get(n
          .getStorageID());
      if (invalidateSet == null) {
        invalidateSet = new LightWeightHashSet<Block>();
        recentInvalidateSets.put(n.getStorageID(), invalidateSet);
      }
      if(!ackRequired){
        b.setNumBytes(BlockFlags.NO_ACK);
      }
      if (invalidateSet.add(b)) {
        pendingDeletionBlocksCount++;
      }
    }
docs: Adds block to list of blocks which will be invalidated on
  specified datanode
  
  @param b block
  @param n datanode