设计模式-09-事件型设计模式

事件型设计模式事件型设计模式常用的四种用于处理事件的设计模式ReactorProactorAsynchronousCompletionTokenAcceptor-Connector.Reactor设计模式描述Reactor模式允许事件驱动的系统复用和分发对服务请求，这些请求来自与一个或多个客户端Reactor有时也叫做Dispatcher,Notifier结构Reactor结构TheReactorarchitecturalpatternallowsevent-drivenapplicationstodemultiplex&dispatchservicerequeststhataredeliveredtoanapplicationfromoneormoreclientsHandleownsdispatches*notifies**handlesetReactorhandle_events()register_handler()remove_handler()EventHandlerhandle_event()get_handle()ConcreteEventHandlerAhandle_event()get_handle()ConcreteEventHandlerBhandle_event()get_handle()SynchronousEventDemuxerselect()<<uses>>Reactor动态过程:MainProgram:ConcreteEventHandler:Reactor:SynchronousEventDemultiplexerregister_handler()get_handle()handle_events()select()handle_event()HandleHandlesHandlesCon.EventHandlerEventsservice()eventObservationsNoteinversionofcontrolAlsonotehowlong-runningeventhandlerscandegradetheQoSsincecallbacksstealthereactor’sthread!InitializephaseEventhandlingphase结构Reactor使用中注意的问题Reactor中注意以下组件事件监听组件的性能和时间间隔有无必要设定定时器事件事件处理采用同步还是异步方式事件处理的调度可否采用队列Proactor设计模式Proactor设计模式允许事件驱动的系统在异步操作完成时触发操作，使得此时系统能够复用和分发系统请求，借此提高并发处理中的性能TheProactor结构ProblemDevelopingsoftwarethatachievesthepotentialefficiency&scalabilityofasyncI/Oishardduetotheseparationintime&spaceofasyncoperationinvocations&theirsubsequentcompletioneventsSolutionApplytheProactorarchitecturalpattern(P2)tomakeefficientuseofasyncI/OHandle<<executes>>*<<uses>>isassociatedwith<<enqueues>><<dequeues>><<uses>><<uses>>Initiator<<demultiplexes

&dispatches>><<invokes>>EventQueueCompletionAsynchronousOperationProcessorexecute_async_op()AsynchronousOperationasync_op()AsynchronousEventDemuxerget_completion_event()Proactorhandle_events()CompletionHandlerhandle_event()ConcreteCompletionHandlerThispatternallowsevent-drivenapplicationstoefficientlydemultiplex&dispatchservicerequeststriggeredbythecompletionofasyncoperations,therebyachievingtheperformancebenefitsofconcurrencywithoutincurringitsmanyliabilitiesProactor动态结构ResultCompletionHandlerCompletion:AsynchronousOperation:ProactorCompletionHandlerexec_async_handle_Resultservice():AsynchronousOperationProcessor:Initiatorasync_operation()Resulthandle_events()eventeventEv.Queueoperation():CompletionEventQueueResultevent()InitiateoperationProcessoperationRuneventloopGenerate&queuecompletioneventDequeuecompletionevent&performcompletionprocessingNotesimilarities&differenceswiththeReactorpattern,e.g.:BothprocesseventsviacallbacksHowever,it’sgenerallyeasiertomulti-threadaproactorAsynchronousCompletionToken

设计模式AsynchronousCompletionToken(异步完成令牌）允许系统在异步操作完成之后及时处理相应。AsynchronousCompletionTokenStructure&ParticipantsDynamicInteractionshandle_event()Acceptor-Connector设计模式Acceptor-Connector（接收器-连接器）封装网络连接成为通讯的对等端点Acceptor-Connector常用于P2P系统当中，分别封装客户端和服务器14Acceptor-Connector结构Handleownsdispatches*notifies**handlesetReactorhandle_events()register_handler()remove_handler()EventHandlerhandle_event()get_handle()ConnectorSynchronousEventDemuxerselect()<<uses>>AcceptorServiceHandlerTheAcceptor-ConnectorPattern<<activate>>owns*usesuses<<creates>>ownsusesowns<<activate>>******usesnotifiesnotifiesnotifiesConnectorConnector()connect()complete()handle_event()ConcreteServiceHandlerBConcreteServiceHandlerAConcreteAcceptorConcreteConnectorAcceptorAcceptor()Accept()handle_event()peer_acceptor_ServiceHandleropen()handle_event()set_handle()peer_stream_Dispatcherselect()handle_events()register_handler()remove_handler()TransportHandleTransportHandleTransportHandleAcceptorDynamicsServiceHandlerEvents:Application:Acceptor:Dispatcherregister_handler()handle_events()accept()open()register_handler()handle_event()service():ServiceHandleropen()ACCEPT_EVENTHandle1Acceptor:Handle2Handle2Handle2Passive-modeendpointinitializephaseServicehandlerinitializephaseServiceprocessingphaseTheAcceptorensuresthatpassive-modetransportendpointsaren’tusedtoread/writedataaccidentallyAndviceversafordatatransportendpoints…ThereistypicallyoneAcceptorfactoryper-service/per-portAdditionaldemuxingcanbedoneathigherlayers,alaCORBASynchronousConnectorDynamicsHandleAddr:Application:Connector:Dispatcher:ServiceHandlerhandle_events()connect()open()register_handler()handle_event()service()ServiceHandlerEventsServiceHandlerHandleget_handle()MotivationforSynchronySyncconnectioninitiationphaseServicehandlerinitializephaseServiceprocessingphaseIftheservicesmustbeinitializedinafixedorder&theclientcan’tperformusefulworkuntilallconnectionsareestablishedIfconnectionlatencyisnegligiblee.g.,connectingwithaserveronthesamehostviaa‘loopback’deviceIfmultiplethreadsofcontrolareavailable&itisefficienttouseathread-per-connectiontoconnecteachservicehandlersynchronouslyAsynchronousConnectorDynamicsAddr:Application:Connector:Dispatcher:ServiceHandlerhandle_events()complete()connect()open()register_handler()handle_event()service()ServiceHandlerConnectorCONNECTEVENTEventsregister_handler()ServiceHandlerHandleHandleHandleget_handle()Motivation