Hermes: A Tutorial and Reference Manual - Researcher - IBM
Hermes: A Tutorial and Reference Manual - Researcher - IBM
Hermes: A Tutorial and Reference Manual - Researcher - IBM
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Ifallalternativesaredisabled,thentheotherwiseclauseisexecuted.If oneormorealternativesareenabled,oneofthemischosen,<strong>and</strong>control transferstothatalternative.However,analternativewithaneventguard canonlybechosenifthatinputporthasatleastonewaitingcallmessage. ports,theselectstatementblocksuntilamessagearrivesatoneofthese Ifalltheenabledalternativeshaveeventguardsreferringtoemptyinput 1.Introductionto<strong>Hermes</strong>27<br />
buer.JustleaveoutthequeuesizetestfromthePutservice. whichcontainsdenitionsfortypesusedinternallybyBoundedBuffer(in nativeisenabledprovidedthenumberoflinesinthequeueislessthan inthequeue.Theotherwiseclause,althoughsyntacticallym<strong>and</strong>atory, canneverbereached.Itiseasytomodifythisprogramintoanunbounded ports.<br />
thiscase,thetypeLinesusedtoimplementthequeue),(2)BBExternal, Capacity,<strong>and</strong>theGetalternativeisenabledprovidedthereareanylines Theboundedbuerprocessusesfourinterfaces:(1)BBLocal(notshown), Inthisexample,theQuitalternativeisalwaysenabled;thePutalter-<br />
buer. languagefeatureswe'vealreadydescribed.Trytowriteityourself<strong>and</strong>then checkwiththedenitionhere: ules,becausetheywillbereusedinapplicationsotherthanthebounded whichdenesthePutLine<strong>and</strong>GetLine,<strong>and</strong>(4)Quit,whichdenesthe interfacefortheQuitoperation.St<strong>and</strong>ard<strong>and</strong>Quitareinseparatemod-<br />
whichdenestheinitializationinterfacefortheboundedbuer,(3)St<strong>and</strong>ard, Theinterfacedenition,BBExternal,isstraightforward,<strong>and</strong>usesonly BBInterface:callmessage( BBExternal:using(Quit,St<strong>and</strong>ard)definitions<br />
BBIn:inportofBBInterfacefinit(Capacity)g; BBOut:outportofBBIn; Capacity:integer,--maximumnumberofmessagesallowed<br />
enddefinitions Put:PutLineOut,--portforwriters<br />
TheQuitdenitionisevensimpler: Get:GetLineOut,--portforreaders<br />
Quit:using()definitions constant(Capacity) exitffullg; Quit:QuitOut)--portforshutdown<br />
object-orientedlanguageslikeSmalltalkInbothcases,wehavetheability enddefinitions Howdoes<strong>Hermes</strong>dierfromdataabstractionlanguageslikeAdaor QuitIn:inportofQuitInterfacefg; QuitInterface:callmessage()exitfg; QuitOut:outportofQuitIn;
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