Friday, August 12, 2016

Oracle BPM 11g/12c: How to Catch an Event in the Same Process

A customer of mine was kind of surprised that when you throw an event in a component of a SCA composite, that the same component cannot catch that event and act upon it. This is a known limitation, for which there is a work-around, which I will discuss in this article.

The work-around is quite simple: another loosely coupled component in the same composite can listen to the event, so all you have to do is to create a BPEL or BPM process as-a-service that is subscribed to the event, and that interacts with the main process that you want to act upon it.

To show that a component cannot listen to its own event, and that the work-around actually works, I used the following test process. No worries, it looks more complex than it is.

The parent process above takes a parameter as input so that I can let it execute either one of the following three scenarios, which consist of throwing an event and then catch it:

  1. In the same (parent) process model
  2. In a reusable sub-process (called through a Call activity)
  3. In a process as-a-service that is called through a Send / Receive activity

There are 4 parallel flows between the OR-gateways:

  • The top flow has a Wait User activity to make it pause and waits for the event.
  • The second flow has a Call Child Call activity which calls the reusable process below.
  • The third flow has the Send/Receive activities to call the process as-a-service below.
  • The bottom one waits 2 seconds to give one of the other flows time to be activated, and then throws either one of two events, depending on whether I want to test catching it in the parent or in the reusable child (for this you cannot use the same event type, that's why).

Only 1 of the first 3 flows is activated at any time, while the last flow (with the events) is always activated. Furthermore the parent process has an Event Sub-process that listens to the event that is thrown by the Throw Internal Event event.

The reusable child is also very basic. It has a User activity to make it pause and wait for the event. It also has a an Event Sub-process that listens to the event that is thrown by the Throw Internal Event for Child event. If it is activated, it will map some variable to itself (to see something concrete in the audit trail), and then it will withdraw the Wait task.
The (child) process as-a-service does the same as the reusable child, except for that it has a start and end event which makes it an asynchronous BPM process as-a-service.
Now when you start an instance of the parent for each of the 3 scenarios, the result in Enterprise Manager is as below:
The instance at the bottom (1450067) belongs to the scenario where the parent tries to catch the event. Which fails as you can see by the fact that it is still running. And yes, I did make sure the Catch Event is correlated properly to the Start Event. The next instance (1450068) is the one that catches it, but as you can see they both are still running. When clicking on the second one, it somehow figured out that both instances are related, but the first instance won't act upon it.

The third instance (1450069) is that of the scenario where the reusable child tries to catch the event. From the fact that there is no other instance, you can see that it does not even listen to the event.

The fourth instance (1450070) is that of the parent that calls the child process as-a-service. The fifth (top) instance (1450071) is that of the child that catches the event, and then calls back the parent instance. As you can see, those are the only two instances that actually completed. So only in this scenario it actually works.