Proactor pattern

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Proactor is a software design pattern for event handling in which long running activities are running in an asynchronous part. A completion handler is called after the asynchronous part has terminated. The proactor pattern can be considered to be an asynchronous variant of the synchronous reactor pattern.[1]


UML Sequence diagram of Proactor

Operation specific actors:

  • The Proactive Initiator starts the asynchronous operation via the Asynchronous Operation Processor and defines the Completion Handler
  • Completion Handler is a call at the end of the operation from the Asynchronous Operation Processor
  • Asynchronous Operation

Standardized actors

  • The Asynchronous Operation Processor controls the whole asynchronous operation
  • The Completion Dispatcher handles the call, depending on the execution environment.


See also[edit]

  • Reactor pattern (a pattern that also asynchronously queues events, but demultiplexes and dispatches them synchronously)


  1. ^ Pattern-Oriented Software Architecture, Volume 2, Schmidt et al., Jon Wiley & Sons, Ltd, 2000

External links[edit]