Operating Systems - CS604 Power Point Slides Lecture 07

7/25/2019 Operating Systems - CS604 Power Point Slides Lecture 07

1/39

Operating

SystemsLecture 7


2/39

January 27, 2016 Copyright Virtual University of Paistan

Agenda for Today

!evie" of previous lecture #he waitan$ execsyste% calls an$

sa%ple co$e

Cooperating processes

Pro$ucer&consu%er pro'le%

(nterprocess co%%unication )(PC* an$process synchroni+ation

!ecap of the lecture


3/39


Review of Lecture 6

che$ulers )long&, an$ short&,

an$ %e$iu%&ter%*

-ispatcher

Process creation an$ ter%ination

forkan$ exit syste% calls


4/39


wait()

#he waitsyste% call suspen$s thecalling process until one of its

i%%e$iate chil$ren ter%inates, or until

a chil$ that is 'eing trace$ stops'ecause it has hit an event of interest.

waitreturns pre%aturely if a signal is

receive$. (f all chil$ren processesstoppe$ or ter%inate$ prior to the call

on wait, return is i%%e$iate.


5/39


Synopsis of wait()

#include

#include

pid_t wait(int *stat_loc);

:/usr/include/sys/types.h


6/39


wait() ...

(f the call is successful, theprocess (- of the ter%inating chil$is returne$.

(f parent ter%inates all its chil$renhave assigne$ as their ne"

parent, the initprocess. #hus thechil$ren still have a parent tocollect their status an$ e/ecution

statistics.


7/39


wait() ...

Zombieprocessa process thathas ter%inate$ 'ut "hose e/it

status has not yet 'een receive$'y its parent process or 'y init.


8/39


Sample Codefork

#include void main()

{

int pid, status;

pid !o"();

i!(pid $%) { p"int!(&!o" !ailed'n);

eit(%);


9/39


Sample Codefork

i!(pid +) { /* hild */ p"int!(&hild he"e-'n);

eit(+);

else { /* a"ent */

wait(status);

p"int!(&0ell done id-'n); eit(+);


10/39


Semantics of fork

P

P

fork


11/39


e!ec()

#ypically the execsyste% call is use$

after a forksyste% call 'y one of the

t"o processes to replace the process

%e%ory space "ith a ne" e/ecuta'le

progra%.

#he ne" process i%age isconstructe$ fro% an or$inary,

e/ecuta'le file.


12/39


e!ec()

#here can 'e no return fro% a

successful exec'ecause the

calling process i%age is overlai$'y the ne" process i%age


13/39


Synopsis of e!ec()

inclu$e 3unist$.h4int e/eclp )const char 5file, const

char 5arg0, ..., const char 5argn,

)char 5*0*


14/39


Sample Codefork

and exec#include void main()

{

int pid, status;

pid !o"();

i!(pid $%) { p"int!(&!o" !ailed'n);

eit(%);

S l C d


15/39


Sample Codefork

and exec i!(pid +) { /* hild */ i! (eeclp(&/1in/ls, &ls, 2344)< +) {

p"int!(&eec !ailed'n);

eit(%);

else { /* a"ent */

wait(status);

p"int!(&0ell done id-'n);

eit(+);


16/39


Semantics of fork

P

P

!o"

pa"ent

child

P

P

pa"ent

child

eec ls

P

ls

pa"ent

child

1 2


17/39


Cooperating "rocesses

Independentprocess cannotaffect or 'e affecte$ 'y the

e/ecution of another process.Cooperatingprocess can affect or

'e affecte$ 'y the e/ecution of

another process


18/39


Cooperating "rocesses

8$vantages of process cooperation (nfor%ation sharing

Co%putation spee$&up

9o$ularity

Convenience


19/39


Para$ig% for cooperating processes,

producerprocess pro$uces

infor%ation that is consu%e$ 'y aconsumerprocess.

unbounded-bufferplaces no practical

li%it on the si+e of the 'uffer

bounded-bufferassu%es that there is

a fi/e$ 'uffer si+e

"roducer#Consumer

"ro$lem


20/39


%ounded#%uffer "ro$lem

ProducerProducer ConsumerConsumer

:%pty Pool

;ull Pool


21/39


%ounded#%uffer Solution

hare$ $ata#de!ine 536678_97 %+

typede! st"uct {

. . . item;

item 1u!!e"536678_97=;

int in +;int out +;

olution is correct, 'ut can only use

:&1 ele%ents


22/39


"roducer "rocess

item net"oduced;

while (%) {

while (((in %) ? 536678_97) out); /* do nothin@ */

1u!!e"in= net"oduced;

in (in %) ? 536678_97;


23/39


Consumer "rocess

item netonsumed;

while (%) {

while (in out); /* do nothin@ */

netonsumed 1u!!e"out=;

out (out %) ? 536678_97;


24/39


&nterprocess

Communication (&"C)9echanis% for processes to

co%%unicate an$ to synchroni+etheir actions.

9essage syste% ? processes

co%%unicate "ith each other"ithout resorting to share$varia'les.


25/39


(PC facility provi$es t"o operations@

Send )message* ? %essage si+e

fi/e$ or varia'le

Receive )message*

&nterprocess

Communication (&"C)


26/39


(f Pan$ Q"ish to co%%unicate,

they nee$ to@esta'lish a communicationlink

'et"een the%

e/change %essages via

sen$Areceive

&nterprocess

Communication (&"C)


27/39


(%ple%entation of co%%unication

linphysical)e.g., share$ %e%ory,

har$"are 'us* logical)e.g., logical properties*

&nterprocess

Communication (&"C)


28/39


&mplementation

'uestions

Bo" are lins esta'lishe$

Can a lin 'e associate$ "ith %orethan t"o processes

Bo" %any lins can there 'e

'et"een every pair of

co%%unicating processes


29/39


&mplementation

'uestions

Dhat is the capacity of a lin

(s the si+e of a %essage that thelin can acco%%o$ate fi/e$ or

varia'le

(s a lin uni$irectional or 'i&

$irectional


30/39


irect Communication

Processes %ust na%e each other

e/plicitly@

send)P, message* ? sen$ a%essage to process P

Receive )Q, message* ? receive a%essage fro% process E


31/39


irect Communication

Properties of co%%unication lin

Lins are esta'lishe$ auto%atically.

8 lin is associate$ "ith e/actly onepair of co%%unicating processes.


32/39


&ndirect Communication

9essages are $irecte$ an$receive$ fro% %ail'o/es )also

referre$ to as ports*.:ach %ail'o/ has a uniFue i$.

Processes can co%%unicate only if

they share a %ail'o/.


33/39



Properties of co%%unication linLin esta'lishe$ only if processes

share a co%%on %ail'o/

8 lin %ay 'e associate$ "ith %anyprocesses.

:ach pair of processes %ay shareseveral co%%unication lins.

Lin %ay 'e uni$irectionalor 'i&$irectional.


34/39


Gperations create a ne" %ail'o/

sen$ an$ receive %essages through

%ail'o/

$estroy a %ail'o/

Pri%itives are $efine$ as@send )A, message*

receive )A, message*



35/39


Mailbox sharing

P1, P2,an$P3share %ail'o/ 8.

P1, sen$s P2an$P3receive.

Dho gets the %essage



36/39


Solutions8llo" a lin to 'e associate$ "ith

at %ost t"o processes.8llo" only one process at a ti%e

to e/ecute a receive operation.

8llo" the syste% to selectar'itrarily the receiver. en$er isnotifie$ "ho the receiver "as.



37/39


Sync*roni+ation

9essage passing %ay 'e either'locing or non&'locing.

Blockingis consi$ere$synchronous

Non-blockingis consi$ere$

asynchronous sendan$ receivepri%itives %ay

'e either 'locing or non&'locing.


38/39


%uffering

Eueue of %essages attache$ to thelin i%ple%ente$ in one of three "ays.

Zero capacity? Ho %essages

en$er %ust "ait for receiver

Bounded capacity? n%essagesen$er %ust "ait if lin full.

Unbounded capacity? infinite length

en$er never "aits.


39/39

J 27 2016 C i ht Vi t l U i

Recap of Lecture

!evie" of previous lecture #he waitan$ execsyste% call an$

sa%ple co$e

Cooperating processes Pro$ucer&consu%er pro'le%

a%ple co$es

(nterprocess co%%unication )(PC* an$

process synchroni+ation

!ecap of the lecture

Operating Systems - CS604 Power Point Slides Lecture 07

Documents

Transcript of Operating Systems - CS604 Power Point Slides Lecture 07