lec3_processes.pptx

7/26/2019 lec3_processes.pptx

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Operating SystemsECE344

Ding Yuan

Lecture 3: Processes


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Ding Yuan, ECE344 OperatingSystem

2

Processes

This lecture starts a class segment that coversprocesses, threads, and synchroniation

These topics are perhaps the most important in this class

You can rest assured that they !ill "e covered in the e#ams

Today$s topics are processes and process management

%hat are the units o& e#ecution'

(o! are those units o& e#ecution represented in the OS'

%hat are the possi"le e#ecution states o& a process'

(o! does a process move &rom one state to another'


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)sers, Programs

)sers have accounts on the system

)sers launch programs

*any users may launch the same program

One user may launch many instances o& thesame program

Then !hat is a process'


3


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4

The Process

The process is the OS a"straction &or e#ecution

+t is the unit o& e#ecution

+t is the unit o& scheduling

+t is the dynamic e#ecution conte#t o& a program

process is sometimes called a-o"or a tas.ora se/uential process

0eal li&e analogy'


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nalogy1 ro"ot ta.ingECE344

Program1 steps &or attending the lecture

Step 1 !al. to 5

Step 21 6nd a seat

Step 31 listen 7or sleep8

Process1 attending the lecture

ction

You are all in the middle o& a process


9


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*acOS e#ample1 ctivity monitor


:


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;inu# e#ample1 ps


1 STTcolumn indicates e#ecution state


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Buestions

%hat state do you thin. a process is in mosto& the time'

or a uniprocessor machine, ho! manyprocesses can "e in running state'

ene6t o& multicore'


5


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Process State raph

Fe! 0eady

0unning

%aiting

Terminated

CreateProcess

ProcessE#it

+AO, Pageault,etc@

+AO Done

ScheduleProcess

)nscheduleProcess


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Process Components

Process State

ne!, ready, running, !aiting, terminatedG

Program Counter

the address o& the ne#t instruction to "e e#ecuted &orthis processG

CP) 0egisters

inde# registers, stac. pointers, general purposeregistersG

CP) Scheduling +n&ormation

process priorityG


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Process Components7cont@8

*emory *anagement +n&ormation

"aseAlimit in&ormation, virtualHphysical mapping, etc

ccounting +n&ormation time limits, process num"erG o!ner

+AO Status +n&ormation

list o& +AO devices allocated to the processG

n ddress Space

memory space visi"le to one process


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Fo! ho! a"out this'

Fo! simultaneously start t!o instances o& this

program *yval 9

*yval :

%hat !ill the outputs "e'


4

intmyval;intmain(int argc, char *argv[]){ myval = atoi(argv[1]);while (1)

printf(myval is %, loc !"%l"#n$, myval, (long) myval);&


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+nstances o& Programs

The address !as al!ays the same

ut the values !ere diIerent

+mplications'

The programs aren$t seeing each other ut they thin. they$re using the same address

Conclusions

addresses are not the =physical memory>

(o!'

*emory mapping

%hat is the "ene6t'Ding Yuan, ECE344 Operating

System:


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into the process$ address space

+nitialies hard!are conte#t and args &or the ne! program

Places the PC onto the ready /ueue

Fote1 +t does notcreate a ne! process

%hat does it mean &or e#ec to return'

%hat does it mean &or e#ec to return !ith an error'


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Ding Yuan, ECE344 OperatingSystem3

Process Creation1 )ni#738

&or.78 is used to create a ne! process, e#ec is used toload a program into the address space

%hy does %indo!s have CreateProcess !hile )ni# uses&or.Ae#ec'

Comparing &or.78 and CreateProcess78' %hich is more convenient to use'

%hich is more e]cient'

%hat happens i& you run =e#ec csh> in your shell'

%hat happens i& you run =e#ec ls> in your shell' Try it@

&or.78 can return an error@ %hy might this happen'

Cannot create child process 7return to parent8@


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Process Termination

ll good processes must come to an end@ ut ho!'

)ni#1 e#it7int status8,%indo!s1 E#itProcess7int status8

Essentially, &ree resources and terminate

Terminate all threads 7ne#t lecture8

Close open 6les, net!or. connections

llocated memory 7and * pages out on dis.8

0emove PC &rom .ernel data structures, delete

Fote that a process does not needto clean up itsel&

%hy does the OS have to do it'


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Physical memory70*8

CopyOn%rite

Lazycopy


c [ 35

" [ 25

a [ 5

c [ 35

" [ 25

a [ 5

5 25 35

Proc@ $s address space Proc@ $s address space

&or.78


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Physical memory70*8

CopyOn%rite

Lazycopy


c [ 35

" [ 25

a [ 5

c [ 45

" [ 25

a [ 5

5 25 35

Proc@ $s address space Proc@ $s address space

&or.78

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Process Termination

%hen e#it78 is called on )ni#1

Threads are terminated 7ne#t lec@8

Open 6les, net!or. connections are closed

ddress space is deallocated ut the PC still remains in the Process Ta"le

Only a parent can remove the PC

Thus completely terminate the process 7called

reap8

Died "ut not yet reaped process is called aom"ie



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!ait78 a second\

O&ten it is convenient to pause until a child processhas 6nished

Thin. o& e#ecuting commands in a shell

)se !ait787%aitorSingleO"-ect8

Suspends the current process until a child process ends

!aitpid78 suspends until the speci6ed child process ends

)ni#1 Every process must "e reaped "y a parent

%hat happens i& a parent process e#its "e&ore a child'

%hat do you thin. a =om"ie> process is'


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)ni# Shells

while (1) {char *cm = rea.comman();int chil.pi = for-();if (chil.pi == !) {

Manipulate STDIN/!T/"## $le descriptors %or pipes&redirection& etc'

e"ec(cm);panic(e"ec faile$);

& else {waitpi(chil.pi);

&&


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Ding Yuan, ECE344 Operating

Process Summary

%hat are the units o& e#ecution' Processes

(o! are those units o& e#ecution represented' Process Control loc.s 7PCs8

(o! is !or. scheduled in the CP)' Process states, process /ueues, conte#t s!itches

%hat are the possi"le e#ecution states o& a process' 0unning, ready, !aiting

(o! does a process move &rom one state to another' Scheduling, +AO, creation, termination

(o! are processes created' CreateProcess 7%indo!s8, &or.Ae#ec 7)ni#8

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lec3_processes.pptx