#vulnerable code 
                                public void setMessageHandler(MessageHandler messageHandler) {
        if (logger.isDebugEnabled())
            logger.debug("Setting the messageHandler for topic: " + origSubData.topic.toStringUtf8()
                         + ", subscriberId: " + origSubData.subscriberId.toStringUtf8());
        synchronized (this) {
            this.messageHandler = messageHandler;
            // Once the MessageHandler is registered, see if we have any queued up
            // subscription messages sent to us already from the server. If so,
            // consume those first. Do this only if the MessageHandler registered is
            // not null (since that would be the HedwigSubscriber.stopDelivery
            // call).
            if (messageHandler != null && subscribeMsgQueue != null && subscribeMsgQueue.size() > 0) {
                if (logger.isDebugEnabled())
                    logger.debug("Consuming " + subscribeMsgQueue.size() + " queued up messages for topic: "
                                 + origSubData.topic.toStringUtf8() + ", subscriberId: "
                                 + origSubData.subscriberId.toStringUtf8());
                for (Message message : subscribeMsgQueue) {
                    asyncMessageConsume(message);
                }
                // Now we can remove the queued up messages since they are all
                // consumed.
                subscribeMsgQueue.clear();
            }
        }
    } 
                            #location 4 
                            #vulnerability type THREAD_SAFETY_VIOLATION
#fixed code
                                public void setMessageHandler(MessageHandler messageHandler) {
        if (logger.isDebugEnabled()) {
            logger.debug("Setting the messageHandler for topic: {}, subscriberId: {}",
                         getOrigSubData().topic.toStringUtf8(),
                         getOrigSubData().subscriberId.toStringUtf8());
        }
        synchronized (this) {
            this.messageHandler = messageHandler;
            // Once the MessageHandler is registered, see if we have any queued up
            // subscription messages sent to us already from the server. If so,
            // consume those first. Do this only if the MessageHandler registered is
            // not null (since that would be the HedwigSubscriber.stopDelivery
            // call).
            if (messageHandler != null && subscribeMsgQueue != null && subscribeMsgQueue.size() > 0) {
                if (logger.isDebugEnabled())
                    logger.debug("Consuming " + subscribeMsgQueue.size() + " queued up messages for topic: "
                                 + origSubData.topic.toStringUtf8() + ", subscriberId: "
                                 + origSubData.subscriberId.toStringUtf8());
                for (Message message : subscribeMsgQueue) {
                    asyncMessageConsume(message);
                }
                // Now we can remove the queued up messages since they are all
                // consumed.
                subscribeMsgQueue.clear();
            }
        }
    }