软件体系结构

软件体系结构3 数据流体系结构DataFlowArchitectures 孙志岗sun sun 2 2020 4 18 Styles MovingfromQualitiestoArchitectures Architecturalstyleshelpsoftwareengineerstoreasonaboutarchitecturalqualities 体系结构风格帮助软件工程师推断软件体系结构的质量 sun 3 2020 4 18 Styles MovingfromQualitiestoArchitectures Astyledescribesaclassofarchitectures描述一类体系结构isfoundrepeatedlyinpractice在实践中被多次设计 应用isapackageofdesigndecisions是若干设计思想的综合hasknownpropertiesthatpermitreuse具有已经被熟知的特性 并且可以复用 sun 4 2020 4 18 ArchitecturalStyles Astyleisdetermined described byasetofcomponenttypes e g datarepository process object 一组组件类型 例如 数据容器 过程 对象 asetofconnectortypes interactionmechanisms e g subroutinecall event pipe 一组连接件类型 交互机制 例如 过程调用 事件 管道 atopologicallayoutofthesecomponents这些组件的拓扑分布 sun 5 2020 4 18 ArchitecturalStyles Astyleisdetermined described byasetofconstraintsontopologyandbehavior e g adatarepositoryisnotallowedtochangestoredvalues pipelinesareacyclic 一组对拓扑和行为的约束 例如 数据容器不能自己改变数据 管道不能是循环的aninformaldescriptionofthecostsandbenefitsofthestyle e g Usethepipeandfilterstylewhenreuseisdesiredandperformanceisnotatoppriority一些对风格的成本和益处的非正式的描述 例如 如果你需要重用性并且性能不是很重要 那么可以使用管道风格 sun 6 2020 4 18 ArchitecturalStyles GarlanandShawcompiledacatalogofarchitecturalstylesin1995 Others suchasBuschmann haveaugmentedthis Thereisnocompletelist 没有完备的列表Thereisnounique non overlappinglist 没有无重叠的列表Stylesoverlap 风格是彼此重叠的Systemsexhibitmultiplestylesatonce 一个系统通常表现出多种风格 sun 7 2020 4 18 TypesofArchitecturalStyles sun 8 2020 4 18 NotesaboutArchitecturalStyles Whenweintroduceanewstyle wewilltypicallyfirstexamineits pure form purearchitecturalstylearerarelyfoundinpractice纯粹的体系风格在实际中很难遇到systemsinpracticeregularlydeviatefromtheacademicdefinitionsofthesesystems 循规蹈矩地背离了对这些系统的学术定义typicallyfeaturemanyarchitecturalstylessimultaneously典型地 融合很多体系风格的特色asanarchitectyoumustunderstandthe pure stylestounderstandthestrengthandweaknessesofthestyleaswellastheconsequencesofdeviatingfromthestyle作为一个架构师 你必须理解 纯 的风格 理解它的优点与缺陷 也要理解背离此种风格之后会带来什么结果 sun 9 2020 4 18 DataFlowStyle 数据流风格 Adataflowsystemisoneinwhichtheavailabilityofdatacontrolsthecomputation由数据控制计算thestructureofthedesignisdominatedbyorderlymotionofdatafromprocesstoprocess系统结构由数据在处理之间的有序移动决定thepatternofdataflowisexplicit数据流系统的结构是显而易见的Inapuredataflowsystem thereisnootherinteractionbetweenprocesses在纯数据流系统中 处理之间除了数据交换 没有任何其他的交互 sun 10 2020 4 18 TheDataFlowStyle Therearevarietyofvariationsonthisgeneratheme howcontrolisexerted e g pushversuspull 如何施加控制 比如 推还是拉 degreeofconcurrencybetweenprocesses并行的程度topology sun 11 2020 4 18 DataFlowStyles Components DataFlowComponentsInterfacesareinputportsandoutputports组件接口是输入端口和输出端口Inputportsreaddata outputportswritedata从输入端口读数据 向输出端口写数据Computationalmodel readdatafrominputports compute writedatatooutputports计算模型 从入口读数 计算 然后写到出口 sun 12 2020 4 18 DataFlowStyles Connectors DataStreamsUni directional 单向 usuallyasynchronous buffered 通常是异步的 有缓冲 Interfacesarereaderandwriterroles接口是reader和writer计算模型 把数据从writer转向readerSystemsArbitrarygraphs 任意拓扑结构 Computationalmodel functionalcomposition 计算模型 功能组合 sun 13 2020 4 18 PatternsofDataFlowinSystems sun 14 2020 4 18 ControlFlowvs DataFlow ControlFlow typicalcaseinproceduralsystems Dominantquestionishowlocusofcontrolmovesthroughtheprogram主要问题是控制点怎样在程序或系统之间移动Datamayaccompanythecontrolbutisnotthedrivingforce数据可能跟着控制走 但是并不起推动系统运转的作用Primaryreasoningisaboutorderofcomputation关注的核心是计算顺序 sun 15 2020 4 18 ControlFlowvs DataFlow DataFlowDominantquestionishowdatamovesthroughacollectionof atomic computations主要问题是数据怎样在运算单元之间流动Asdatamoves controlis activated 数据到了 控制 计算 单元便开始工作Wereasonaboutdataavailability transformations latency 我们关心数据是否可用 转换 潜伏 sun 16 2020 4 18 ThreeExamplesofDataFlow BatchSequential 批处理 Pipe and Filter 管道 ProcessControl 控制 sun 17 2020 4 18 BatchSequentialPattern sun 18 2020 4 18 CharacteristicsofBatchSequentialSystems Processingstepsareindependentprograms每个处理步骤是一个独立的程序Eachsteprunstocompletionbeforenextstepstarts每一步必须在前一步结束后才能开始Datatransmittedasawholebetweensteps数据必须是完整的 以整体的方式传递Typicalapplications classicaldataprocessingprogramcompilation computeraidedsoftwareengineering sun 19 2020 4 18 CharacteristicsofBatchSequentialSystems ArchitecturalHeuristicscomponents processingsteps areindependentprogramsconnectorsaresometypeofmedia traditionallymagnetictapeeachsteprunstocompletionbeforethenextstepbegins sun 20 2020 4 18 Example BatchSequentialSystems Compilersearlycompilersbeganasessentiallybatchsequentialsystemslexicalanalysis parsing semanticanalysis codegenerationinitiallyamechanismtoturnhigherlevelsourcecodeintoobjectcodeComputerAidedSoftwareEngineeringCASEtoolsinitiallyprovidedanenvironmenttowriteandcompilesourcecodeintoobjectcodecompiler library linker make intoanintegratedtoolearlytoolswereindependentprogramslatertoolssharedonlyfilescommonformats simplesharingmechanisms scriptseventuallytoolsgrewtoincludedesign documentation configurationcontrol andevenautomaticcodegeneration sun 21 2020 4 18 ThreeExamplesofDataFlow BatchSequential 批处理 Pipe and Filter 管道 ProcessControl 控制 sun 22 2020 4 18 Pipe and Filter sun 23 2020 4 18 PipesandFilters Roleof pure filtersreadsstreamsofdataasinput producesstreamsofdataasoutputtraditionallybyte orientedperformsstream to streamtransformationsenrichdatabycomputationandaddinginformation通过计算和增加信息丰富数据refinebydistillingdataorremovingirrelevantdata通过浓缩和删除精炼数据transformdatabychangingitsrepresentation通过改变记录方式转化数据 sun 24 2020 4 18 PipesandFilters incrementallytransformdatafromthesourcetothesink 递增地转化数据 dataisprocessedasitarrives notgatheredthenprocessed数据到来时便被处理 不是收集然后处理 偶有例外 filtersareindependententitiesnocontextinprocessingstreamsnostatepreservationbetweeninstantiationsnoknowledgeofupstream downstreamfiltersthecorrectnessoftheoutputshouldnotdependupontheorderinwhichthepipesareconnectedinapipe and filternetwork过滤器的先后顺序不影响输出的结果 sun 25 2020 4 18 Pipe and Filter Roleof pure pipes SG96 movedatafromafilteroutputtoafilterinput ortoadeviceorfile datamovesinonedirection upstreamflowcontrolisallowedpipesformdatatransmissiongraphsOverallOperationsystemactionismediatedbydatadelivery数据传送引起系统动作pipe and filtersystemsrununtilnomoredataisavailableandnomorecomputationspossible sun 26 2020 4 18 Pipes and Filters inunix unixprocessesthattransformstdintostdoutaregenerallycalledfiltersbutwhentheyconsumealltheinputbeforestartingtheoutput theyviolatethefilterassumptionsort forexampleunixpipescantreatfilesaswellasfiltersasdatasourcesandsinksbutfilesarepassive soyoucan tmakearbitrarycombinationsunixassumesthatthepipescarryASCIIcharacterstreamsthegoodnews anythingcanconnecttoanythingelsethebadnews everythingmustbeencodedinASCII thenshipped thendecoded sun 27 2020 4 18 Pipes and Filters inunix sun 28 2020 4 18 Issue DataPullingandDataPushing Question whatistheforcethatmakesthedataflow Threechoices allwithforceemanatingfromfilters push datasourcepushesdataindownstreamdirectionpull datasinkpullsdatafromupstreamdirectionpush pull afilterisactivelypullingfromupstream computing andpushingdownstreampassive don tdoeither actasasinkfordataCombinationsmaybecomplex Ifmorethanonefilterispushing pulling synchronizationisneededSo Whycan tyoupipeafiletoafileinunix sun 29 2020 4 18 BatchSequentialvsPipe Filter sun 30 2020 4 18 BatchSequentialvsPipe Filter UNIX BothDecomposetaskintofixedsequenceofcomputationsInteractonlythroughdatapassedfromonetoanother把任务分解成为一系列固定顺序的计算单元 组件 组件间只通过数据传递交互 sun 31 2020 4 18 BatchSequentialvsPipe Filter UNIX sun 32 2020 4 18 AVariantonDataFlow Issue insomesystems DataflowsslowlythroughthesystemDatadoesnotremainstrictlyinorder sun 33 2020 4 18 Summary GuidanceforSelectingaDataFlowStyle taskisdominatedbytheavailabilityofdata任务由数据主导datacanbemovedpredictablyfromprocesstoprocess事先知道数据的确切流向pipe and filterarchitecturesaregoodchoicesformanydataflowapplicationsbecausetheypermitreuseandreconfigurationoffiltersgen