Feature Coordination Patterns

Feature design involves defining the sequence of messages that will be exchanged between tasks. When designing a feature one of the tasks in the feature should be identified as the Feature Coordinator. The main role of the Feature Coordinator is to ensure that the feature goes to a logical completion. No feature should be left in suspended animation because of message loss or failure of a single task involved in the message interactions.

In most cases, the task coordinating the feature will be running a timer to keep track of progress of the feature. If the timer times out, the coordinator will take appropriate recovery action to take the feature execution to a logical conclusion, i.e. feature success or failure.

Feature coordination can be achieved in several ways. Some of the frequently seen design patterns are described here. The description is in terms of four tasks A, B, C and D that are involved in a feature. A is the feature coordinator in all cases.

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