tailieunhanh - An Object Behavioral Pattern for Demultiplexing and Dispatching Handles for Synchronous Events

The cache diffusion algorithm then works as follows. Every time the root basestation receives a tuple that does not join, it sends the maximal ERD which that tuple inter- sects one hop in the direction that the tuple came from. This node then checks its local value cache for tuples that are contained within this ERD. If one is found, this value and any other values that overlap with the ERD are re- moved from the local value cache, and the ERD is added to the ERD cache table with priority 1. If no match is found, then the ERD. | Reactor An Object Behavioral Pattern for Demultiplexing and Dispatching Handles for Synchronous Events Douglas C. Schmidt schmidt@ Department of Computer Science Washington University St. Louis MO1 An earlier version of this paper appeared as a chapter in the book Pattern Languages of Program Design ISBN 0201-6073-4 edited by Jim Coplien and Douglas C. Schmidt and published by Addison-Wesley 1995. 1 Intent The Reactor design pattern handles service requests that are delivered concurrently to an application by one or more clients. Each service in an application may consist of serveral methods and is represented by a separate event handler that is responsible for dispatching service-specific requests. Dispatching of event handlers is performed by an initiation dispatcher which manages the registered event handlers. Demultiplexing of service requests is performed by a synchronous event demultiplexer. 2 Also Known As CLIENT NETWORK CLIENT DATABASE PRINTER SOCKET HANDLES CONSOLE CLIENT LOGGING RECORDS Figure 1 Distributed Logging Service CONNECTION REQUEST LOGGING RECORDS LOGGING SERVER SERVER Dispatcher Notifier 3 Example To illustrate the Reactor pattern consider the event-driven server for a distributed logging service shown in Figure 1. Client applications use the logging service to record information about their status in a distributed environment. This status information commonly includes error notifications debugging traces and performance reports. Logging records are sent to a central logging server which can write the records to various output devices such as a console a printer a file or a network management database. The logging server shown in Figure 1 handles logging records and connection requests sent by clients. Logging records and connection requests can arrive concurrently on multiple handles. A handle identifies network communication resources managed within an OS. The logging server communicates with clients using a connection-oriented .