Pattern-Oriented Software Architecture, Volume 2, Patterns for Concurrent and Networked Objects

Asynchronous Completion Token

The Asynchronous Completion Token design pattern allows an application to demultiplex and process efficiently the responses of asynchronous operations it invokes on services.

Also Known As

Active Demultiplexing [PRS+99], ‘Magic Cookie’

Example

Consider a large-scale distributed e-commerce system consisting of clusters of Web servers. These servers store and retrieve various types of content in response to requests from Web browsers. The performance and reliability of such e-commerce systems has become increasingly crucial to many businesses.

For example, in a web-based stock trading system, it is important that the current stock quotes, as well as subsequent buy and sell orders, are transmitted efficiently and reliably. The Web servers in the e-commerce system must therefore be monitored carefully to ensure they are providing the necessary quality of service to users. Autonomous management agents can address this need by propagating management events from e-commerce system Web servers back to management applications:

System administrators can use these management agents, applications, and events to monitor, visualize, and control the status and performance of Web servers in the e-commerce system [PSK+97].

Typically, a management application uses the Publisher-Subscriber pattern [POSA1] to subscribe with one or more management agents to receive various ...