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ProcessesinUnix,Linux,andWindowsCS502OperatingSystems(SlidesincludematerialsfromOperatingSystemConcepts,7thed.
,bySilbershatz,Galvin,&GagneandfromModernOperatingSystems,2nded.
,byTanenbaum)GenericProcesses–ReviewProcessstate–informationmaintainedbyOSforrepresentingprocess,inPCBPSW,registers,conditioncodes,etc.
Memory,files,resources,etc.
Priority,blockingstatus,etc.
QueuesReadyQueueSemaphorequeuesOtherkindsofqueuesnotyetcovered(e.
g.
,fordisks,communicationresources,etc.
)GenericProcesses–Review(continued)InterruptsandtrapsSwitchingcontextsSavingstateofoneprocessLoadingstateofanotherprocessSchedulingDecidingwhichprocesstorun(orserve)nextMorenextweekInterprocessCommunicationLaterinthecourseReadingAssignmentChapter3ofSilbershatzEspecially:§3.
1–3.
3Process(withcapital"P")AProcessinUnix,Linux,orWindowscomprises:–anaddressspace–usuallyprotectedandvirtual–mappedintomemorythecodefortherunningprogramthedatafortherunningprogramanexecutionstackandstackpointer(SP)theprogramcounter(PC)asetofprocessorregisters–generalpurposeandstatusasetofsystemresourcesfiles,networkconnections,pipes,…privileges,(human)userassociation,……Processes–AddressSpace0x000000000xFFFFFFFFVirtualaddressspaceprogramcode(text)staticdataheap(dynamicallyallocated)stack(dynamicallyallocated)PCSPSeealsoSilbershatz,figure3.
1ProcessesintheOS–RepresentationTousers(andotherprocesses)aprocessisidentifiedbyitsProcessID(PID)IntheOS,processesarerepresentedbyentriesinaProcessTable(PT)PIDisindexto(orpointerto)aPTentryPTentry=ProcessControlBlock(PCB)PCBisalargedatastructurethatcontainsorpointstoallinfoabouttheprocessLinux-definedintask_struct–over70fieldsseeinclude/linux/sched.
hNT–definedinEPROCESS–about60fieldsProcessesintheOS–PCBTypicalPCBcontains:executionstatePC,SP&processorregisters–storedwhenprocessisnotinrunningstatememorymanagementinfoPrivilegesandownerinfoschedulingpriorityresourceinfoaccountinginfoProcess–startingandendingProcessesarecreated…WhenthesystembootsBytheactionsofanotherprocess(morelater)BytheactionsofauserBytheactionsofabatchmanagerProcessesterminate…Normally–exitVoluntarilyonanerrorInvoluntarilyonanerrorTerminated(killed)bytheactionsauseroraprocessProcesses–SwitchingWhenaprocessisrunning,itshardwarestateisintheCPU–PC,SP,processorregistersWhentheOSsuspendsrunningaprocess,itsavesthehardwarestateinthePCBContextswitchistheactofswitchingtheCPUfromoneprocesstoanothertimesharingsystemsmaydo100sor1000sofswitches/sectakes1-100microsecondsontoday'shardwareProcesses–StatesProcesshasanexecutionstateready:waitingtobeassignedtoCPUrunning:executingontheCPUwaiting:waitingforanevent,e.
g.
I/OProcesses–StateQueuesTheOSmaintainsacollectionofprocessstatequeuestypicallyonequeueforeachstate–e.
g.
,ready,waiting,…eachPCBisputontoaqueueaccordingtoitscurrentstateasaprocesschangesstate,itsPCBisunlinkedfromonequeue,andlinkedtoanotherProcessstateandthequeueschangeinresponsetoevents–interrupts,trapsProcesses–PrivilegesUsersaregivenprivilegesbythesystemadministratorPrivilegesdeterminewhatrightsauserhasforanobject.
Unix/Linux–Read|Write|eXecutebyuser,groupand"other"(i.
e.
,"world")WinNT–AccessControlListProcesses"inherit"privilegesfromuserProcesses–CreationUnix/LinuxCreateanew(child)process–fork();AllocatesnewPCBClonesthecallingprocess(almost)CopyofparentprocessaddressspaceCopiesresourcesinkernel(e.
g.
files)PlacesnewPCBonReadyqueueReturnfromfork()call0forchildchildPIDforparentExampleoffork()intmain(intargc,char**argv){char*name=argv[0];intchild_pid=fork();if(child_pid==0){printf("Childof%sseesPIDof%d\n"name,child_pid);return0;}else{printf("Iamtheparent%s.
Mychildis%d\n",name,child_pid);return0;forktestChildofforktestseesPIDof0Iamtheparentforktest.
Mychildis486StartingNewProgramsUnix&Linux:–intexec(char*prog,char**argv)CheckprivilegesandfiletypeLoadsprogram"prog"intoaddressspaceReplacingpreviouscontents!
Executionstartsatmain()Initializescontext–e.
g.
passesarguments*argvPlacePCBonreadyqueuePreserves,pipes,openfiles,privileges,etc.
ForkingaNewProgramfork()followedbyexec()CreatesanewprocessascloneofpreviousoneFirstthingthatclonedoesistoreplaceitselfwithnewprogramFork+Exec–shell-likeintmain(intargc,char**argv){char*argvNew[5];intpid;if((pid=fork())<0){printf("Forkerror\n");exit(1);}elseif(pid==0){/*childprocess*/argvNew[0]="/bin/ls";argvNew[1]="-l";argvNew[2]=NULL;if(execve(argvNew[0],argvNew,environ)<0){printf("Execveerror\n");exit(1);}}else{/*parent*/wait(pid);/*waitforthechildtofinish*/}}Processes–NewProgramsWindows/NT–combinesfork&execCreateProcess(10arguments)NotaparentchildrelationshipNote–privilegesrequiredtocreateanewprocessWindows,Unix,andLinux(traditional)ProcessesareinseparateaddressspacesBydefault,nosharedmemoryProcessesareunitofschedulingAprocessisready,waiting,orrunningProcessesareunitofresourceallocationFiles,I/O,memory,privileges,…Processesareusedfor(almost)everything!
ANoteonImplementationManyOSimplementationsinclude(partsof)kernelineveryaddressspaceProtectedEasytoaccessAllowskerneltoseeintoclientprocessesTransferringdataExaminingstate…Processes–AddressSpace0x000000000xFFFFFFFFVirtualaddressspacecode(text)staticdataheap(dynamicallyallocated)KernelCodeandDataPCSPUserSpacestack(dynamicallyallocated)KernelSpace32-bitLinux&WinXP–3G/1Guserspace/kernelspaceLinuxKernelImplementationKernelmayexecuteineitherProcesscontextvs.
InterruptcontextInProcesscontext,kernelhasaccesstoVirtualmemory,files,otherprocessresourcesMaysleep,takepagefaults,etc.
,onbehalfofprocessInInterruptcontext,noassumptionaboutwhatprocesswasexecuting(ifany)Noaccesstovirtualmemory,files,resourcesMaynotsleep,takepagefaults,etc.
ProcessesinOtherOperatingSystemsImplementationswilldifferSometimesasubsetofUnix/Linux/WindowsSometimesquitedifferentMayhavemorerestrictedsetofresourcesOften,specializeinreal-timeconstraintsQuestionsImplementationReadyqueuePCBPCBPCBPCBSemaphoreAcount=0PCBPCBSemaphoreBcount=2