Setting Up Message Handlers

Setting up a Listener/Message Handler

To subscribe to messages in a queue, a Message Handler Flow needs to be configured. This will be used to interpret and run actions on messages received from the queue.

The following example will demonstrate how to pull messages from a configured RabbitMQ. A similar process will be involved for other message queues.

1. From a Designer Project, create a new Flow.
2. Navigate to the Properties Panel for the Flow. Under the SETTINGS category, select the drop-down menu under Behavior Type and select Message Queue Handler Flow.
   
   Choosing this Flow behavior provides three additional Flow Inputs; Message, Handler Id, and Headers. The Message Input contains the Payload (Byte[]), Id (String), and MessageDateTime (DateTime) Inputs.
3. From Toolbox, navigate to DATA > TEXT and attach a Get String From UTF 8 Bytes step to the Start step. 
4. On the Properties panel under INPUTS, click Unknown and select Select From Flow. Click Message, select Payload, and click DONE. 
   RabbitMQ Messages are typically encoded in UTF8. Other messengers may use Base 64, Ascii, or a different UTF decoding step to help decode the Payload.

   

5. Attach a Show Popup step from Toolbox > FAVORITE STEPS to the workspace. Map GetStringFromUTF8Bytes1_Output to Message, and Constant map the desired Subject. 

   

6. Click Save to save changes to the Flow.

Subscribing to a Queue

The messaging system Queue will need to be configured in order for Decisions to subscribe to it.

1. If a Queue has not been added, navigate to the desired Designer Folder > Settings > Jobs & Events > Message Queues. Click ADD RABBIT QUEUE from the Global Action Bar. 
2. From the Add Rabbit Queue window, define the Message Queue parameters and click SAVE. 

   

Connect Processing Flow to Queue

The following demonstrates a Message Queue Handler. The setting options can be overridden to specify different servers or queues by navigating to System > Jobs and Events > Message Queues, creating a message queue, and selecting the Override Server Info option.

1. Navigate to the desired Designer Folder > Settings > Jobs and Events > Message Queue Handlers. Click ADD MESSAGE HANDLER.
2. From the Add Message Handler window, define the desired Handler Name, select the desired Message Handling behavior, define the Active Flow Count, create or pick the Message Handler Flow, then select the Message Queue. Click SAVE.  

Thread Fine-Tuning

Starting in v9.4 users are able to configure how many threads are created to handle message queues. They can also specify how long those threads should exist when they are idle. This can help increase performance by dismissing unneeded threads.

The settings are found when first creating a Message Handler or when editing its registration entity.

1. Checking the Fine-Tune Thread Behavior option will bring up the setting for configuring the maximum number of threads to create field. It will also cause the Stop Threads When Idle option to appear.
2. Checking the Stop Threads When Idle option opens up the options for idle threads and the sliders to choose how long the thread can remain idle.

Feature Changes