You can encapsulate asynchronous operations within an active object. An active object creates one or more threads to asynchronously execute service requests made by its clients.

This is useful because IOUs (described in The IOU Classes) are not always closed and redeemed when threads exit. Although the RWTThreadIOUFunction class closes the IOU just before exiting, it is possible to create threads that can close an IOU at any time during their processing.