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]

This article relies largely or entirely on a single source. (March 2024)

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.

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

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