Processes (OS2 L1&2)

Question 1

Processes

Answer 1

program in execution (with restricted rights)- dynamic entity executing or ready to execute

Question 2

Job

Answer 2

unit of work in a time sharing/multi-tasking OS

Question 3

how does a user create a process

Answer 3

double click

cmd

Question 4

What happens when two copies of a program are running two separate processes

Answer 4

OS generally smart enough to not duplicate resources and allow these processes to share those that they can share

Question 5

Relationship between process and the OS kernel

Answer 5

process is the abstraction for protected execution provided by the operating system kernel
process needs permission from kernel before accessing memory of any other process - amongst other things
Kernel maps user process to be executed by hardware?

Question 6

True/False - programs can spawn other processes

Answer 6

True, they can also be an execution environment for other processes

Question 7

Parent process

Answer 7

spawns children processes - forming a tree of processes. Processes are identified by PID

Question 8

innit systemd launchd

Answer 8

examples of parent processes that are the parent of all other processes on the system 
first process executed
manages all other processes
started by kernel
PID = 1

Question 9

Program’s execution context

Answer 9

basically, surrounding info needed for running the process effectively

• state of processor (processor context) which is the value of its program counter and all registers
• process memory map - identifies various regions in memory that have been allocated to the process

Question 10

Process lists

Answer 10

used to keep track of processes

each entry is a process control block - contains info that kernel needs to know about the process

Question 11

process groups

Answer 11

groups of process that are related so that they can be signaled
every process is a member of a group

Question 12

Fields in PCB

Answer 12

process state
program counter
CPU registers - contents of all process centric registers
CPU scheduling information - priorities etc
Mem management information - mem allocated to process
Accounting info - cpu used, clock time elapsed
I/O status information - i/o devices allocated to process

Question 13

for( )

Answer 13

create new process

Question 14

wait( )

Answer 14

e.g. parent can call wait( ) and wait for child to finish executing before executing itself

Question 15

exec( )

Answer 15

overlays a process - replaces a process’s mem space with a new program

Question 16

Resource sharing options between parent and children

Answer 16

share all resources
children share subset of parent resources
no sharing

Question 17

Execution options for parent and children processes - after fork( )

Answer 17

execute concurrently

parents wait until children terminate

Question 18

Address space option for parent and children processes

Answer 18

duplicated

child has other program loaded into it

Question 19

how many processes per processor at a time

Answer 19

1

Question 20

new state

Answer 20

process being created

Question 21

running

Answer 21

instructions being executed

Question 22

waiting

Answer 22

process waiting to event to occur

Question 23

ready

Answer 23

process waiting to be assigned to a processor

Question 24

terminated

Answer 24

process finished execution

Question 25

“System is in the context of that process”

Answer 25

When a process is running its said that System is in the context of that program

Question 26

What needs to be saved during a context switch

Answer 26

enough information so that the kernel can switch back to the earlier process and continue from the exact same place it left off

Question 27

Short term scheduler

Answer 27

selects process to be executed next, invoked frequently

Question 28

long term scheduler

Answer 28

selects processes to be brought into the ready queue. - controls the degree of multitasking

Question 29

i/o bound processes

Answer 29

spend more time doing i/o - many short cpu bursts

Question 30

cpu bound processes

Answer 30

spend more time doing computations - few long cpu bursts

Question 31

Reasons for IPC (cooperating processes)

Answer 31

information sharing
Computation speedup - parallelization
Modularity

Question 32

name the two IPC models

Answer 32

shared memory

message passing

Question 33

explained shared memory as an IPC model

Answer 33

two or more processes agree to remove restrictions (relating to preventing one process from accessing another’s memory) and exchange information by reading and writing data to shared areas

Question 34

explained message passing as an IPC model

Answer 34

send() receive() - parents and children can send messages via a pipe

Question 35

what happens upon process termination?

Answer 35

executes last statement and asks OS to delete it using exit( ). On exit a process may return status value (typically an int) to waiting parent process. On exit all process resources are reclaimed by OS

Question 36

why is a terminate system call only allowed to be invoked by parent process?

Answer 36

otherwise user or misbehaving application could kill another process
parent needs to know identities of children to terminate them

Question 37

why would a parent process terminate its child process

Answer 37

child exceeded allocated resources
Task assigned to child is no longer required
parent is exiting and OS does not allow child with out a parent

Question 38

zombie process

Answer 38

A zombie process or defunct process is a process that has completed execution but still has an entry in the process table as its parent process didn’t invoke an wait() system call.

Question 39

Orphan process

Answer 39

An orphan process is a computer process whose parent process has finished or terminated, though it (child process) remains running itself.