Processes and Threads

Question 1

what is a process in relation to a program?

Answer 1

a program is a bunch of instructions on a strorage medium, a process is a unit of work being executed on a computer. a program is run as one or more processes

Question 2

what functions of processes does an OS facilitate? (5)

Answer 2

• creation
• deletion
• scheduling
• communication
• syncronisation

Question 3

what are 5 states a process can be in?

Answer 3

• new
• ready
• running
• waiting
• terminated

Question 4

what is a PCB?

Answer 4

a process control block is an OSs representation of a process, held in a table or list

allows OS to suspend a running process and later restore its state

Question 5

what is a context switch?

Answer 5

switching the CPU between execution of processes. the context is the process state, stored in the PCB list or table. there is no useful work done while switching

Question 6

what do parents and children share?

Answer 6

when forking, the child gets a copy of the address space and they share file handlers. they are identical apart from their pid

Question 7

what do threads share?

Answer 7

Share file desc and process space, have their own stacks and registers, can write to each other’s variables. Can communicate easily via variables.

have their own registers and stack

Question 8

what is overwritten when exec is called?

Answer 8

everything, except the process id and file descriptors

Question 9

how can processes share memory?

Answer 9

shm_open and mmap(). creates shared memory in heap

Question 10

why are threads useful?

Answer 10

a process has its own private address space and its inconvient for IPC and expensive to switch contexts

useful in a server handling incoming connections, or a word processer waiting for input