OS Section 03 Processes

8/9/2019 OS Section 03 Processes

1/20

3: Processes 1

Jerry Breecher

OPERATING SYSTEMS

PROCESSES


2/20

3: Processes 2

What Is In This Chapter?

Process Definition Scheduling Processes What Do Processes Do?

Inter-process Communication

OPERATING SYSTEM

Processes


3/20

3: Processes 3

PROCESSESPROCESS CONCEPT:

A pro ra! is passive; a process active. Attributes held b a process include

hard!are state" memor "

CP#" progress $e%ecuting&

W"Y "A#E PROCESSES?

'esource sharing $ logical $files& and ph sical$hard!are& &.

Computation speedup - ta(ing advantage of multiprogramming ) i.e. e%ample of acustomer*server database s stem.

+odularit for protection.

$e%initions


4/20

3: Processes 4

PROCESSES PROCESS STATE Ne& ,he process is ust being put together.

R'nnin Instructions being e%ecuted. ,his running process holds the CP#. Waitin or an event $hard!are" human" or another process.&

Rea(y ,he process has all needed resources - !aiting for CP# onl .

S'spen(e( Another process has e%plicitl told this process to sleep. It !ill bea!a(ened !hen a process e%plicitl a!a(ens it.

Ter!inate( ,he process is being torn apart.


5/20

3: Processes 5

PROCESS CONTRO) B)OC*:

C/0,AI0S I0 /'+A,I/0 ASS/CIA,1D WI,2 1AC2P'/C1SS3

It4s a data structure holding3

PC" CP# registers" memor management information" accounting $ time used" ID" ... & I*/ status $ such as file resources &" scheduling data $ relative priorit " etc. & Process State $so running" suspended" etc. is simpl

a field in the PC5 &.

PROCESSES Process State


6/20

3: Processes 6

,he act of Sche('+in a process means changing the active PC5 pointed to b the CP#. Also called a conte,t s&itch-

A conte%t s!itch is essentiall the same as a process s!itch - it means that the memor "as seen b one process is changed to the memor seen b another process. See .i 're on Ne,t Pa e /0-12

SC"E$3)ING 43E3ES:

$Process is driven b events that are triggered b needs and availabilit &

'ead 6ueue 7 contains those processes that are read to run.

I*/ 6ueue $!aiting state & 7 holds those processes !aiting for I*/ service.

What do the 6ueues loo( li(e? ,he can be implemented as single or double lin(ed.See .i 're Se5era+ Pa es %ro! No& /0-02

PROCESSESSche('+inCo!ponents


7/20

3: Processes 7


,he CP# s!itchingfrom one process toanother.


8/20

3: Processes 8

.i 're 0-0


Rea(y 4An(

IO 46s


9/20

3: Processes 9

)ONG TERM SC"E$3)ER

'un seldom $ !hen ob comes into memor &

Controls degree of multiprogramming

,ries to balance arrival and departure rate through an appropriate ob mi%.

S"ORT TERM SC"E$3)ER

Contains three functions3

Code to remove a process from the processor at the end of its run.a&Process ma go to read 6ueue or to a !ait state.

Code to put a process on the read 6ueue )a&Process must be read to run.b&Process placed on 6ueue based on priorit .



10/20

3: Processes 10

S"ORT TERM SC"E$3)ER /cont-2

Code to ta(e a process off the read 6ueue and run that process $also called(ispatcher &.

a& Al!a s ta(es the first process on the 6ueue $no intelligence re6uired&

b& Places the process on the processor.

,his code runs fre6uentl and so should be as short as possible.

ME$I3M TERM SC"E$3)ER

+i%ture of CP# and memor resource management.

S!ap out*in obs to improve mi% and to get memor .

Controls change of priorit .



11/20

3: Processes 11

INTERR3PT "AN$)ER In addition to doing device !or(" it also readies processes" moving them" for

instance" from !aiting to read .

"o& (o a++

thesesche('+in

co!ponents%it to ether?

.i 0-7


Interr'pt "an(+er

Short Ter!Sche('+er

Short Ter!Sche('+er

)on Ter!Sche('+er

Me(i'! Ter!Sche('+er


12/20

3: Processes 12

What nee(s to 8e (one on a process sche('+e?

What nee(s to 8e (one on a threa( sche('+e?

What is a conte,t s&itch?

PROCESSESSche('+in Processes

an( Threa(s


13/20

3: Processes 13

Parent can run concurrentl !ith child"or !ait for completion.

Child ma share all $for(* oin& or partof parent4s variables.

Death of parent ma force death ofchild.

Processes are static $never terminate&or d namic $ can terminate &.

In(epen(ent 1%ecution isdeterministic and reproducible.1%ecution can be stopped* started!ithout affecting other processes.

Cooperatin 1%ecution depends onother processes or is time dependent.2ere the same inputs !on4t al!a sgive the same outputs; the processdepends on other e%ternal states.

PROCESSESProcess

Re+ationships


14/20

3: Processes 14

This is ho& processes ta+9 to each other-

,here are basicall t!o methods3

Share( !e!ory $!ith a process 8(ic(8& -- fast* no data transfer.

Messa e Passin -- distributed* better isolation.

MET"O$S O. IMP)EMENTATION:

Direct or indirect - to process or mailbo%. S mmetric or as mmetric? 5uffering mechanism Send b cop or b reference? i%ed or variable si9e messages?

.3NCTIONA)ITY O. COMM3NICATION)IN*S:

2o! are the lin(s formed? 2o! man processes on each lin(? 2o! man lin(s per pair of processes? Capacit - buffer space - can messages

be en6ueued. +essage formats and si9es #ni- or bidirectional

PROCESSESInterprocess

Co!!'nication


15/20

3: Processes 15

$IRECT COMM3NICATION:

0eed to (no! name of sender*receiver. +echanism loo(s li(e this3

sen( $ Process:P" message & ;

recei5e $ Process: " message &;

recei5e $ id" message &


16/20

3: Processes 16

Other properties o% $irect Co!!'nication:

=in( established automaticall $!hen send or receive re6uested.& /nl t!o processes in this form. /ne lin( per pair of processes. >enerall 5i-directional 'eceiver ma not need ID of sender.

$isa(5anta e o% $irect Co!!'nication:

,he names of processes must be (no!n - the can4t be easil changed since the aree%plicitl named in the send and receive.


Co!!'nication


17/20

3: Processes 17

IN$IRECT COMM3NICATION

Processes communicate via a named mailbo% rather than via a process name.+echanism loo(s li(e this3

open $ mailbo%:name &; sen( $ mailbo%:name" message &; recei5e $ mailbo%:name" message&;

=in( is established if processes have a shared mailbo%. So mailbo% must be establishedbefore the send*receive.

+ore than t!o processes are allo!ed to use the same mailbo%.

+a cause confusion !ith multiple receivers - if several processes have outstandingreceives on a mailbo%" !hich one gets a message?


Co!!'nication


18/20

3: Processes 18

B3..ERING:

/ptions include3 ero -- sender must !ait for recipient to get message. Provides a rende9vous.

Bo'n(e( -- sender must !ait for recipient if more than n messages in buffer.

3n8o'n(e( -- sender is never dela ed.

MESSAGE .ORMAT:

i%ed" ariable" or , ped $as in language t ping& si9e messages.

Send reference rather than cop $good for large messages&.

Suspended vs. unsuspended sends.


Co!!'nication


19/20

3: Processes 19

Re!ote proce('re ca++ $'PC& abstractsprocedure calls bet!een processes onnet!or(ed s stems.

St'8s ) client-side pro% for the actualprocedure on the server.

,he client-side stub locates the server andmarshalls the parameters.

,he server-side stub receives this message"unpac(s the marshalled parameters" and

peforms the procedure on the server.


Co!!'nication


20/20

3: Processes 20

WRAP3P

PROCESSES

We65e +oo9e( in (etai+ at ho& processes &or9- Speci%ica++y &e65e

@ Seen ho& they et sche('+e( /an( st'(ie( sche('+ers in (oin so2;@ #isite( the actions that can 8e per%or!e( on o8

OS Section 03 Processes

Documents

Transcript of OS Section 03 Processes