What is the Reactor pattern?

Mark Pollack

The new book "Pattern-oriented Software Architecture Volume 2" ISBN 0471606952 has a chapter on the Reactor pattern. It falls under the general category of "Event Handling Patterns". To quote the leading bit of the chapter,

"The Reactor architectural pattern allows event-driven applications to demultiplex and dispatch service requests that are delivered to an application from one or more clients"

It is used in a synchronous manner, so that if the callback you delegate the event to takes a while to complete you will run into problems with scalability.