CICS讲义.docx
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CICS讲义.docx
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CICS讲义
1.Ataskistheexecutionofanapplication
program.
•Multitasking:
Twoormoretaskscan
executeatthesametime.
•Multithreading:
Twoormoreuserscan
accessthesamecopyofaprogramat
thesametime.
2.UnderCICS,ausercannotdirectlyinvoke
aprogram.Instead,theuserinvokesa
transaction,whichinturnspecifiesthe
applicationprogramtoberun.
•Whenauserinvokesatransaction,CICS
locatestheapplicationprogram
associatedwiththetransaction,loadsit
intomainstorage(ifitisn’tinstorage
already),andstartsatask(runningthat
program).
3.Thedifferencebetweenataskanda
transactionisthatwhileseveralusers
mayinvokethesametransaction,each
isgivenaseparatetask.
•Eachtransactionisidentifiedbyaunique
four-charactercodecalledatransaction
identifier,ortrans-id
4.PCT(ProgramControlTable).
•Basically,thePCTisalistofvalid
transactionidentifiers.Eachtrans-idin
thePCTispairedwiththenameofthe
programCICSwillloadandexecute
whenthetransactionisinvoked.
5.PPT(ProcessingProgramTable)
•AnotherCICStablecalledtheProcessing
ProgramTable,orPPT,containsalistofall
validprogramnames.Thistablekeepstrack
ofwhichprogramsarelocatedinstorage.•CICSusesPPTtodeterminewhetheranew
copyofaprogramneedstobeloadedinto
storagewhenatransactionisinvoked.
•CICStablessuchasPCT,PPTarecreated
bysystemprogrammersandusedby
applicationprogrammers.
6.PCT(ProgramControlTable)
Trans-idApplicationProgram
ODR1-----------------ORDPGM1
PAY1-----------------PAYROLL
TRN1-----------------TRNPGM1
7.PPT
TRNPGM1….1…..(onecopyinstorage)
ORDPGM1….1.….(onecopyinstorage)
PAYROLL....0…..(notinstorage)
:
8.Howatransactionworks
1.Auserentersthetrans-idTRN1.Then,
CICSsearchestheProgramControlTable
(PCT)tofindtheprogramtobeexecuted.
2.ThenCICSsearchestheProcessing
ProgramTable(PPT)todetermineifthe
programiscurrentlyinmainstorage.Ifitisn’t,
thenCICSlocatestheprogramondisk,loads
itintostorage,updatesthePPT,andinitiates
anewtask.
9.EachterminalintheCICSsystemmustbe
definedintheTerminalControlTable
(TCT).Eachterminalinthistableisassigneda
uniqueone-tofour-characterterminalidentifier,
orterm-id.
10.EachfileaccessedbyCICSmustbedefinedinthe
FileControlTable,orFCT.TheFCTspecifiesthefile
name,alongwithotherinformationsuchasthefiletype
(F,V)andtheoperations(read/write/update…)thatcan
beperformedonthefile.
11.CICSservices:
a)1.Thedatacommunicationservicesallowusers
tocommunicatewithprogramsthroughtheir
terminals.
i.Howanapplicationprogramcommunicateswith
terminaldevices?
•Terminalcontrolletsyousendtextor
receivetextfromtheterminalthatinitiatedthe
task.
•BasicMappingSupport(BMS)letsyou
createmapsthatspecifythepositionandthe
characteristicsoftheindividualdisplayelements
ontheterminalscreen.
b)Thedatamanagementservicesletprograms
accessdatastoredinfilesordatabases
i.CICSprovidesthreeservicestomanagedata:
file
control,SQL,andDL/I.(3waystoaccessdataon
disk)
1.Filecontrolpassesdatarequestsmadebya
programtoVSAM.VSAM,inturn,managesthedata
storedinfilesonDASD.
2.SQLforDB2
3.DL/IforIMS
12.CICScreatesatasktoprocessa
transactionthatisinitiatedbytheuser
enteringatransactionIDintothesystem.A
CICStaskistheinternalrepresentationof
theuser’stransaction.
•InCICS,itispossibleformultipleusersto
enterthesametransactionIDatthesame
time(concurrently).CICScreatesa
uniquetask(task-id)torepresenteach
transaction.Therefore,severaltasksmay
bereadyandwaitingforexecutionatany
givenmoment.
13.There’rethreemajorstagesinatask’s
lifecycle:
1.Readytoexecute
2.Executing
3.Waiting(waitingforaservice,
usuallyanI/O,tocomplete)
14.Whileonetaskiswaiting,a
secondtaskcanexecute.ThisishowCICS
achievesconcurrency.
15.Thestepsinthetransactionprocessing
cycleare:
•AtransactionIDenterstotheCICS
system.
•CICScreatesataskthatisreadyto
execute.Severaltaskscanbeat‘readyto
execute’stageatonetime.
•CICSdispatchesthetaskthatshould
executenext.
•Thetaskexecutes.Thetaskinvokesaprogramandpassescontroltoit.
TheprogramcallsCICStoperforma
serviceonitsbehalfsuchasaterminal
orfileI/Ooperation.
•Thetaskwaitsfortheservicesto
complete.Anothertaskisdispatched
whilethefirstoneiswaiting.
•TheserviceiscompletedandtheCICS
taskisre-dispatchedforexecution.
•TheprogramissuesaRETURNcommand
andCICSterminatesthetaskandrelease
resources
16.Multitasking–TheCICSallowsmorethan
onetasktobeexecutedatthesametime.
•Multithreading–Allowsalltheusersina
CICSregiontousethesamecopyofa
programatthesametime.Formultithreading
towork,theprogrammustbereentrant.
•atrulyreentrantprogramcannot
modifydatainworkingstorage.
•CICSaccomplishesmultithreadingby
providingaseparatecopyofworking
storageforeachuserrunningtheprogram
17.TraditionalCICSBMStasksissuereceivemap,
processtransactionlogic,sendmap,andreturn
controltoCICS.Theycanbefurtherclassified
intoPseudo-conversationaland
conversational.
•AnumberofprogramsmayparticipateinaCICS
transaction.EXECCICSLINKandEXECCICS
XCTLaretheusualAPI.
18.CICSprogramsdonotusestatementssuchas
ACCEPT,DISPLAY,READ,WRITE,OPEN,and
CLOSE.InsteadtheyissueCICScommandsto
performterminalI/O,fileI/O,Programloadingand
control,andotherfunctionsrequiringanexternal
resource.
•AllCICScommandshavetheformat:
EXECCICS
commandoptions…
END-EXEC.
•CICSprogramscanbewritteninCOBOL,C++,
JAVA,Assemblerand….Nomatterwhichlanguage
isused,thebasicformatofCICScommandsisthe
same.
19.Thedifferencebetweenatask
andatransactionisthatwhileseveralusers
mayinvokethesametransaction,eachis
givenaseparatetask
20.CEDA
•CICScreatestheseinternalcontroltables
basedonresourcedefinitionscreatedby
systemsprogrammers.
•SystemsprogrammersuseResource
DefinitionOnline(RDO)todefine
resourcessuchastransactionsand
programsfromaCICSterminal.
•Trans-idforRDOisCEDA,RDOis
sometimesreferredtoasCEDA.
21.CESF-Signoff
•CESF–SignofffromtheCICSsystem.
YourterminalremainsconnectedtoCICS.
•CESFLOGOFF–SignofffromtheCICS
anddisconnectyourterminalfromCICS.
22.CEMT-MastTerminalfunctions
•Toinvokeallthemasterterminalfunctions.
•Byusingthisfunction,anoperatorcaninquire
aboutandchangethevaluesofCICSsystem
parameters,alterthestatusofthesystem
resources,terminatetasks,andshutdown
theCICSsystem.
•CEMTcanalsoopen/closeafile,
enable/disableatrans-id/program,bringina
newcopyofprogram,etc
23.CEOT-toinquireaboutthestatusofyour
owntermiCWTO-WritemessagesTotheconsoleOperator.
24.CWTO‘Systemslow!
’
‘Systemslow!
’willbesenttooperatorconsole.
25.CMSG–MessageSwitching.Tosendmessages
fromyourterminaltoanotherterminal.
CMSG‘Systemiscomingdownat22:
00’,R=all,S
CMSG‘HellofromDenny’,R=term-id,S
term-id:
istheterminalthatyousendthemessagetonal
26.CEDF–theExecutionDiagnosticFacilityusedto
debugaprogram.Usedfortestingapplication
programsthatareassociatedwithuser
transactionsinitiatedfromaterminal.
27.CEDA–DefineresourcestoCICSsystem.
Resources:
program,mapset,file,transaction
28.Torunyourapplicationsystem,youneedto
supplyCICSwithinformationaboutyour
systemresources,includingsoftware
resourcessuchasfiles,programs,
mapsets,andtransactions,andhardware
resourcessuchasterminals,printers
29.Onthefirstlineofthisscreen,youcanseethename
ofthemap(inqmap1)that’susedtodisplaythis
screenandthetrans-id(INQ1)that’susedtostartthe
program.Inaddition,youcanseethenameofthe
program,CustomerInquiry.Thisinformationhelps
theuseridentifythemapandtheprogramthat
displaysit.
30.Aconversationalprogramisanonlineprogram
thatsitsidle(空闲)whileitwaitsforuserinput.(like
screen1)
•Whenaconversationalprogramfirststarts,it
sendsitsinitialmaptotheterminal.Then,it
entersintoaloopwhileitwaitsforinput,
retrievestheinputdatafromtheterminal,
processesthedata,sendsitsoutputtothe
terminal,andwaitsagain.
•Whileaconversationalprogramwaitsforuser
input,thetaskassociatedwiththatprogram
(resource)remainsinstorage.Becauseofthat,
conversationalprogramsareinefficientinterms
ofvirtualstorageusage.
a)Conversationalprogramsareoftenthe
causeofaCICSconditionknownasShort
onStorage,orSOS.
•WhenCICSgoesshortonstorage(SOS),it
suspendsallworkandbegins
terminatingtasksinanefforttofreeup
storage
31.Howpseudo-conversational
programmingworks
•Thesolutiontotheinefficienciesof
conversationalprogramsistoremovethetask
associatedwithaprogramfromstoragewhile
theprogramiswaitingforterminalinput.
•Forexample,whilethemapforthecustomer
inquiryprogramisdisplayed,theinquiryprogram
itselfhasterminatedanditstaskisnolongerin
storage.Whentheuserentersanothercustomer
numberandpressestheEnterkey,theinquiry
programisrestarted.Theresultisthatthe
taskisinstorageonlywhenitneedstobe:
whentheprogramisprocessingdata
a)Becausepseudo-conversational
programsusemainstorageando
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