code: void addMessageHandler(SubscriptionMessageHandler messageHandler)
    {
      if (TraceComponent.isAnyTracingEnabled() && tc.isEntryEnabled())
        SibTr.entry(tc, "addMessageHandler", messageHandler);
  
      final boolean inserted = _subscriptionMessagePool.add(messageHandler);
      // If the message wasn't inserted, then the pool was exceeded
      if (!inserted)
        if (TraceComponent.isAnyTracingEnabled() && tc.isDebugEnabled())
          SibTr.debug(
            tc,
           "SubscriptionObjectPool size exceeded");
  
      if (TraceComponent.isAnyTracingEnabled() && tc.isEntryEnabled())
        SibTr.exit(tc, "addMessageHandler");
    }
docs: Adds a message back into the Pool of available messages.
  
  @param messageHandler The message handler to add back to the pool