OPERATING SYSTEMS: Lesson 3: Introduction to Process ...ocw.uc3m.es/ingenieria-informatica/operating...Operating Systems Process • Process: Program in execution. – Each execution

OperatingSystems

OPERATING SYSTEMS:

Lesson 3:Introduction to Process Management

1

Jesús Carretero PérezDavid Expósito SinghJosé Daniel García SánchezFrancisco Javier García BlasFlorin Isaila

OperatingSystems

Contents

¨Processconcept.¨Basiclifecycleofaprocess.¨Processinformation¨Multitasking.¨Contextswitch.¨Generatinganexecutable.

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OperatingSystems

Process

• Process:Programinexecution.– Eachexecutionofaprogramleadstoaprocess.– Processistheunitofmanagementforoperatingsystem

• Aprocessconsistsof:– Programtext:Instructions.– Setofdataassociatedtoprogramexecution.

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OperatingSystems

Programexecution

ExecutableProgram

A

Mai

n M

emor

y

Process A1

Process A2

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OperatingSystems

Memoryrepresentation

• Aprocessneedsmemoryforinstructionsanddata.

• Differentinstancesofaprogramneedindependentareasfordata.

text

data

heap

stack

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OperatingSystems

Contents


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OperatingSystems

Basiclifecycleofprocess

Running

BlockedReady

Wait an event

End of event blocking

Time-slicefinished

Activation

As many asprocessors

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New processes

Fin

OperatingSystems

Simplifiedqueuingmodel:Singleprocessor

Processor

Ev 1

New processes Finished processes

Ev 2

Ev 3…

End of time-slice

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OperatingSystems

Simplifiedqueuingmodel:Multipleprocessors

Processor

Ev 1

New processes

Ev 2

Ev 3

…

End of time-slice

FinishedProcesses

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OperatingSystems

Contents


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OperatingSystems

Processinformation

• Alltheinformationallowingtheprocesscorrectexecution.

• Threecategories:– Informationstoredintheprocessor.– Informationstoredinmemory.– Additionalinformationmanagedbyoperatingsystem.

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OperatingSystems

Processorstate

¨Processorstateincludesvaluesofprocessorregisters.¤Registersaccessibleinusermode.

¤ Generalregisters: Registerfile.¤ Programcounter.¤ Stackpointer.¤ Userpartinstatusregister.

¤Registersaccessibleinprivilegedmode:n Privilegedpartfromstatusregister.nMemorymanagement registers(e.g.PTBR).

¨Contextswitch:¨ Saveprocessorstateforoutgoingprocess.¨ Restoreprocessorstateforincomingprocess.

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OperatingSystems

Memoryimageofaprocess

¨Memoryimageconsistsofthememoryspacesthataprocessisauthorizedtouse.

¨Ifaprocessgeneratesanaddressoutoftheaddressspace,hardwaregeneratesatrap.

¨Dependingonspecificcomputer,memoryimagemaybereferredtovirtualmemoryorphysicalmemory.

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OperatingSystems

Memoryimagemodels:Singleregion

• Processwithasinglefixedsizeregion.– Usedinsystemswithoutvirtualmemory.

• Processwithasinglevariablesizedregion.– Systemswithoutvirtualmemory:

• Needreservespace" Memorywaste.

– Systemswithvirtualmemory:• Virtualreservespace" Feasiblebutlessflexiblethanmultipleregion.

• Notused.

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OperatingSystems

Memoryimagemodels:Multipleregions

• Processwithfixednumberofregionsofvariablesize.– Prefixedregions(text,data,stack).– Eachregionmaygrow.– Withvirtualmemory,theholebetweenstackandheapdoesnotconsumeresources.

text

data

stack

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OperatingSystems

Memoryimagemodels:Multipleregions

• Processwithvariablenumberofregionsofvariablesize.– More advancedoption(usedincurrentversionsinWindowsandUNIX).

– Processstructuredasanumberofregions.– Veryflexible:

• Sharedregions.• Regionsmaydifferinpermissions.

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OperatingSystems

Operatingsysteminformation

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• Operatingsystemkeepsadditionalinformationonprocesses.

• Operatingsystemkeepsinformationinatable:ProcessTable.

• ProcessControlBlock (PCB):Eachentryintablekeepsinformationaboutoneprocess.

• AlmostallinformationaboutprocessstoredinPCB.nSomeinformationelementskeptoutsideduetoimplementationreasons.

OperatingSystems

Example:•Process identification.•Parent process identification.•User information.

ContenidosdelBCP

• Identificationinformation.

• Processorstate.• Processcontrolinformation.

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On process start:•Initial values for processor state.After context switch:•Copy state values to processor.

Scheduling and state information:•Process state.•Waited event (if blocked).•Process priority.•Scheduling information.Allocated regions description.•Per region information.Allocated resources:•Open files.•Used communication ports.•Timers.Pointers for structuring process queues (or rings).Information for inter process communication.

OperatingSystems

InformationoutofPCB

• NotalltheinformationreferredtoaprocessisstoredinitsPCB.

• Decisiontakeninfunctionof:– Efficiency.

• Tablesshouldhaveaprefixedsizeandalwaysbeinmemory.• Sizeneedstobeoptimized.

– InformationSharing.• IfdataneedstobeshareditcannotbeinthePCB.• Pointersareusedtopointtootherstructures (tables)allowingforinformation sharing.

– Openfiles.– Memorypages.

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OperatingSystems

PageTable

• PlacedoutsidePCB.

• Describesprocessmemoryimage.• PCBcontainspointertopagetable.• Reasons:

– Variablesize.– MemorysharingamongprocessesrequiresittobeexternaltoPCB.

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OperatingSystems

Filepositionpointers

• PlacedoutsidePCB.

• Ifaddedtoopenfilestable(inPCB)cannotbeshared.

• Ifassociatedtoi-nodeisalwaysshared.

• StoredinacommonstructureformultipleprocessesandanewoneallocatedwithOPENservice.

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OperatingSystems

Example:Runningacommand

#include <sys/types.h>

#include <stdio.h>int main(int argc, char** argv) {pid_t pid;pid = fork();switch (pid) {

case -1: /* error */exit(-1);

case 0: /* proceso hijo */if (execvp(argv[1], &argv[1])<0) { perror(“error”); }break;

default:printf(“Proceso padre”);

}

return 0;}

prog cat f1

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OperatingSystems

Forkservice

• pid_t fork(void);

¨ Duplicatesprocessinvokingthecall.¨ Parentprocessandchildprocessgoonrunningthesameprogram.¨ Childprocessinheritsopenfilesfromparentprocess.

¨ Openfiledescriptorsarecopied.¨ Pendingalarmsaredeactivated.

• Returns:– -1onerror.– Inparentprocess:childprocessdescriptor.– Inchildprocess:0.

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OperatingSystems

Forkservice

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Process A

Process A’

FORK

OperatingSystems

Execservice

• Singleservicewithmultiple libraryfunctions.int execl(const char *path, const char *arg, ...);int execv(const char* path, char* const argv[]);int execve(const char* path, char* const argv[], char* const envp[]);int execvp(const char *file, char *const argv[])

• Changescurrentprocessimage.– path:pathtoexecutable file.– file:LooksfortheexecutablefileinalldirectoriesspecifiedbyPATH.

• Description:– Returns-1onerror,otherwiseitdoesnotreturn.– Thesameprocessrunsanotherprogram.– Openfilesremainopen.– Signalswithdefaultactionremaindefaulted,signalswithhandlertakedefault

action.

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OperatingSystems

Execservice

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Process A

Proceso A’

EXEC

Process B

OperatingSystems

Exitservice

• Finalizesprocessexecution.

void exit(status);

• Allopenfilesdescriptorsareclosed.• Allprocessresourcesarereleased.• PCB (ProcessControlBlock)isreleased.

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OperatingSystems

Contents


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OperatingSystems

Operatingsystemtypes

Operating Systems

Multiprocess(several processes

running)

Multiuser(several users

at a time)

Monouser(a single user

at a time)

Monoprocess(single process)

Monouser(a single user at a

time)

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OperatingSystems

Principlesofmultitasking

• RealparallelismbetweenI/OandCPU(DMA).• ProcessalternatebetweenI/Oandprocessingphases.

• Severalprocessesstoredinmemory.

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OperatingSystems

Advantagesofmultitasking

• Easesprogramming,dividingaprograminmultipleprocesses(modularity).

• Allowssimultaneousinteractiveserviceofmultipleusersinanefficientway.

• TakesadvantageoftimesaprocessspendswaitingforanI/Ooperationtobecompleted.

• IncreasesutilizationofCPU.

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OperatingSystems

Multiprogrammingdegree

• Multiprogrammingdegree:Numberofactiveprocesses.

• Mainmemoryneeds:Systemwithoutvirtualmemory.

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100%

Multiprogramming degree

% C

PU u

tiliz

atio

n

OperatingSystems

Multiprogramming:CPUuse

1 process

2 processes

Execution

I/O

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OperatingSystems

Multiprogrammingandvirtualmemory

• Systemswithvirtualmemory:– Divideaddressingspaceofprocessesinpages.– Dividephysicalmemoryaddressingspaceinmainmemoryinpageframes.

• Atagiventime,eachprocesshasacertainnumberofitspagesinmainmemory(residentset).

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OperatingSystems

Memoryneeds:Virtualmemorysystem

Page

fram

es p

er p

roce

ss


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OperatingSystems

Performance:Smallphysicalmemory

¨Whenmultiprogrammingdegreeincreases:¨ Residentsetsize

decreasesforeachprocess.

¨TrashinghappensbeforeachievingahighCPUutilizationpercentage.

¨Solution:Addmoremainmemory.

100%


% C

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n

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OperatingSystems

Performance:Largephysicalmemory

• Whenmultiprogrammingdegreeincreases:– Residentsetsizedecreasesfor

eachprocess.

• HighCPUutilizationpercentageisachievedwithlessprocessesthatfitinmemory.

• Solution:Improveprocessororaddmoreprocessors.

100%


% C

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OperatingSystems

Contents


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OperatingSystems

Contextswitching

• Whenoperatingsystemassignsprocessortoanewprocess.

• Actions:– SaveprocessstateinPCBforprocessinexecution.– Restorestateofnewprocessinprocessor.

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OperatingSystems

Contextswitch

Save state in PCB0

Restore state from PCB1

Save state in PCB1

Restore state from PCB0

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OperatingSystems

Contextswitchingtypes

¨Voluntarycontextswitch:¤ Processperformscalltooperatingsystem(orgeneratesexceptionlike

pagefault)implyingwaitingforanevent.¤Running" Blocked.¤ Examples:readingfromterminal,pagefault.¤Reason⇒ Processoruseefficiency.

¨ Involuntarycontextswitch:¤OSappropriatesCPU.¤Running" Ready.¤ Examples:timesliceellapsed orprocessmovesfromblockedtoready

andhashigherpriority.¤Reason⇒ Processorusesharing

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OperatingSystems

Contents


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OperatingSystems

Executablegeneration

Linker (ld)

Compiler

a.c

a.o

Compiler

b.c

b.o

p

Relocatable object files separately generated

Executable object file (contains code and data for all defined functions in a.c and b.c).

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OperatingSystems

LinkEditor(linker)

n Combinesobjectfiles:¨ Mergesseveralrelocatableobjectfiles(.o)inasingle

executableobjectfile:inputforloader.

n Resolvesexternalreferences:¨ Referencestosymbolsdefinedinotherobjectfile.

n Relocatessymbols:n Fromrelativepositionsin.otoabsolutepositionsin

executable:adjustrefstothesenewpositions.n Symbols:refstofunctionsanddata.

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OperatingSystems

Ejemplo:FormatoELF

n ELF:ExecutableandLinkableFormat

¨ formatobinarioestándarparaficherosobjeto¨ originaldeSystemVà BSD,Linux,Solaris¨ formatounificadopara:

n ficherosobjetoreubicablesn ficherosobjetoejecutablesn ficherosobjetocompartidos

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OperatingSystems

ELFformat

ELF header

Program header table(required for executables)

.text section

.data section

.bss section

.symtab

.rel.txt

.rel.data

.debug

Section header table(required for relocatables)

0

Code

“block started bysymbol” Non-

initialized staticdata

Type (.o, .exe, .so, etc); machine; Big /Little end; etc

Symbol table

Relocationinfo

Iinitialized staticdata

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OperatingSystems

Executableload

ELF header

Program header table(required for executables)

.text section

.data section

.bss section

.symtab

.rel.text

.rel.data

.debug

Section header table(required for relocatables)

0

.text segment(r/o)

.data segment(initialized r/w)

.bss segment(uninitialized r/w)

Process image

0x08048494

init and shared libsegments

0x080483e0

Virtual addr

0x0804a010

0x0804a3b0

MEMORYDISK

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OperatingSystems

Staticlibrary

Compiler

a.c

a.o

Compiler

b.c

b.o libc.aStatic library: file with contatenation of relocatableobject files.

Executable object file: includes code from functions in libc used in the program.

Linker (ld)

p

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OperatingSystems

Staticanddynamiclibraries

n Drawbacksofstaticlibraries:¨ Codepotentiallyduplicatedinexecutables:

¨ Disk(filesystem).¨ Virtualmemoryspaceinprocesses.

¨ Bugsinlibraries" newversion" needtorelink

n Solution:dynamiclibraries(*.so) (dynamiclinklibraries,DLLs):n Componentsloadedinmemoryandexecutedatruntime.n Functionsfromlibrariesmaybesharedamongmultipleprocesses.

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OperatingSystems

Dynamiclibraries

Functions from libc.so and invoked from a.c and b.c are loaded and linked.Potentially shared among multiple processes.

Shared library

Compiler

a.c

a.o

Compilerb.c

b.o

libc.so

Linker (ld)

p

Cargador / Enlazador dinámico

(ld-linux.so)

Executable in memory P’50

OperatingSystems

Reminder

¨ Differencebetweenprogramandprocess.¨ Aprocessisaporgram inexecution.

¨ Operatingsystemmanagesrunningprocesses(processlifecycle).¨ Processinformationconsistingof:processstate,memoryimage

andPCB.¨Multitaskingallowsabetteruseofcomputerresources.¨ Contextswitchingintroducesasmalloverhead.¨ Staticlibrariesarelinkedatcompiletimewhiledynamiclibraries

arelinkedatprocesscreationtime.¨ Processcreationimpliescreationofitsmemoryimageandthe

allocationofaPCB.

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OperatingSystems

OPERATING SYSTEMS:

Lesson 3:Introduction to Process Management

52

Jesús Carretero PérezDavid Expósito SinghJosé Daniel García SánchezFrancisco Javier García BlasFlorin Isaila

Documents

OPERATING SYSTEMS: Lesson 3: Introduction to Process ...ocw.uc3m.es/ingenieria-informatica/operating...Operating Systems Process • Process: Program in execution. – Each execution