WebSphere Business Integration Adapters: An Adapter Development and WebSphere Business Integration Solution

Chapter 9. Synchronous event processing (callback) 147

scenario two, you would need to enhance your design to enable process multiple

concurrent sequential event requests.

9.4 Adapter termination and sequential event

processing

This section describes the different behaviors of adapter termination when you

use sequential event processing.

9.4.1 Normal termination

When an adapter is shut down normally, the Adapter Framework attempts to call

the termination method of the custom connector agent class. This method should

undertake the necessary processing to terminate the sequential processing

mechanism. We recommend that any currently awaiting requests be handled by

returning a failure status to the back-end application, if at all possible.

Current, in-progress requests will most likely be lost or might need to be thrown

away depending on the connectivity to the application. When an adapter is

terminated, a sequential event request will likely be in one of three states:

 Awaiting processing by the sequential event processing mechanism

 Sent to the broker and awaiting a response

 Processing the broker response to send back to the application

The first point has been discussed previously, and ideally, we would prefer to

process any currently available responses prior to returning from the terminate

method of the custom adapter agent, which can be achieved with thoughtful

adapter design. One consideration that adapter developers should take into

account is the longevity of the broker flows or processes that might be executed.

Ideally, these processes should be short-lived. If this cannot be guaranteed, the

adapter developer must consider weighing the implications of delaying adapter

termination and risk the user pressing Ctrl+C to terminate the adapter abnormally

or terminating the adapter with outstanding requests.

9.4.2 Abnormal termination or no neat adapter shutdown situations

If a custom adapter with sequential event processing is abnormally terminated,

the back-end application will be potentially left in state where it is awaiting

responses from the adapter that it will never receive. Action might be required

within the application to clean-up the application state.

148 WebSphere Business Integration Adapters

In addition, depending on the broker, you can find messages on the

Synchronous Response Queue. On adapter startup, these response messages

are no processed, because the Adapter Framework cannot correlate the

response message with any currently outstanding sequential event processing

requests within the adapter.