@Override
    public String toString() {
      StringBuilder sb = new StringBuilder();
      sb.append("StateStabilizedMessage ");
      sb.append(processorId);
      if (super.getSender() != null) {
        sb.append(" from ");
        sb.append(super.getSender());
      }
      if (!getRecipients().isEmpty()) {
        String recip = getRecipientsDescription();
        sb.append(" to ");
        sb.append(recip);
      }
      sb.append(" on behalf of ");
      sb.append(sendingMember);
      ReplyException ex = getException();
      if (ex != null) {
        sb.append(" with exception ");
        sb.append(ex);
      }

      return sb.toString();
    }
the member for whom this ack is being sent
geode-core/src/main/java/org/apache/geode/internal/cache/StateFlushOperation.java