@Override
  public Object putAttribute(String attr, Object value) {
    Object obj = attributes.put(attr, value);
    deltas.put(attr, new DeltaEvent(true, attr, value));
    flush();
    return obj;
  }
{@inheritDoc} Put an attribute, setting the dirty flag and immediately flushing the delta
queue.
extensions/geode-modules-session-internal/src/main/java/org/apache/geode/modules/session/internal/filter/attributes/DeltaSessionAttributes.java