public LongUpdater reserveLong() {
    if (ignoreWrites) {
      return null;
    }
    checkIfWritable();
    ensureCapacity(8);
    LongUpdater result = new LongUpdater(buffer);
    buffer.putLong(0L);
    return result;
  }
Reserves space in the output for a long and returns a LongUpdater than can be used to update
this particular long.

@return the LongUpdater that allows the long to be updated
geode-serialization/src/main/java/org/apache/geode/internal/serialization/BufferDataOutputStream.java