Concurrent message processing

[dartvandru]

Events with the same eventType and swimlane MUST BE processed sequentially. All other events can and should be processed concurrently.

In the Java code, SwimlaneBasedDispatcher.java maintains a separate queue of events for each swimlane (BUG it should be eventType and swimlane). A thread based mechanism pulls events from the queue and processes them one at a time. NodeJS doesn’t have threads but I’d imagine a callback-based messaging would be good:

• When the processing of one message completes, get the next message from the queue if there is one
• Each queue keeps track of whether processing is happening so that after adding an event to the queue:
  • If not processing, start processing
  • If processing, do nothing - event will be processed eventually