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]

Interaction

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.

Implementations

• Proactor and Boost.Asio (C++)
• Adaptive Communication Environment (C++)
• RJR (Ruby)

See also

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

References

External links

• Proactor - An Object Behavioral Pattern for Demultiplexing and Dispatching Handlers for Asynchronous Events, Irfan Pyarali, Tim Harrison, Douglas C. Schmidt, Thomas D. Jordan, 1997 (pdf 143 kB)