Mod 1: Introduction

Question 1

What is concurrency?

Answer 1

(1) Concept of managing multiple tasks,
(2) Two or more things happening (seemingly) at the same time,
(3) Several tasks making progress, sharing CPU

Question 2

What is a task?

Answer 2

Unit of a program

Question 3

What is parallell programming?

Answer 3

(1) When two or more tasks run at the same time (actually, not seemingly),
(2) NOT sharing the computer’s CPU,
(3) Requires at least two cores in the CPU (if only one)

Question 4

With the support of which three is concurreny achieved?

Answer 4

(1) The underlying hardware
(2) The Operating system
(3) The application

Question 5

What is a “scheduler”?

Answer 5

Program runned by the OS or Runtime, deciding which process should run within the next period of time

Question 6

What is the purpose of a scheduler?

Answer 6

Decide which process should be allowed to run within the next period of time

Question 7

What are the two types of scheduling?

Answer 7

(1) Preemptive
(2) Cooperative

Question 8

What is preemptive sheduling?

Answer 8

> priority-based
gives every task exclusive access to a computing resource for a given time
common i multitasking OS

Question 9

What is cooperative scheduling?

Answer 9

Mechanism that give every task exclusive access until the task is done, or let the computing resource go

Question 10

What is an interrupt?

Answer 10

Signal to the processor produced by hardware or software indicating an event needing immediate attention

Question 11

What does multitasking refer to?

Answer 11

It refers to

(1) the OS ability to run more than one process at the time,
(2) utilizing one or more CPU resources

Question 12

Give an example of multitasking

Answer 12

Multithreading

multitasking within an application, executing several tasks concurrently

Question 13

What is a process?

Answer 13

Application in execution

Question 14

What does a process consists of?

Answer 14

(1) Program instructions
(2) Stack memory/Call Stack
(3) A heap memory
(4) Program counter (register)
(5) Other resources eg. security info

Question 15

Does two different processes share memory space?

Answer 15

No

Question 16

What is the relationship between a process , a thread and a task?

Answer 16

(1) Both are units of execution
(2) A threads runs within the address space of process, whilst the process run in it’s on space isolated from other processes
(3) Every process has at least one thread
(4) Every thread performs a task
(5) A task is unit of work that is to be scheduled

Question 17

How is concurrency accomplished on a single processor/core?

Answer 17

Time-slicing

Question 18

What defines a concurrent application?

Answer 18

Application containing two or more processes (or threads) that work together to perform a task

Question 19

What is the difference between a sequential application and a concurrent application?

Answer 19

A sequential application has one single thread of execution and a concurrent application has multiple threads of execution

Question 20

How does communication between processes take place?

Answer 20

By using shared variables or message passing

Question 21

What is “Parallelism”?

Answer 21

It refers to the ability to perform multiple tasks simultaneously

Question 22

How can we achieve parallelism in an application?

Answer 22

By splitting the application into smaller tasks where they can be executed in parallel

Question 23

What is the difference between concurrency and parallelism?

Answer 23

Concurrency: running seemingly at the same time (eg. so short intervals it gives the illusion of running parallel)

Parallelism: running exactly at the same time (eg. two applications run purely parallel, each in a separate processor)

Parallelism can be considered as a form of concurrency.

Question 24

Can parallelism be considered a form of concurrency?

Answer 24

Yes

Question 25

What is multithreading about?

Answer 25

Using more than on thread in an application, executing at the same time within the process

Question 26

What is the main advantage of multithreading?

Answer 26

(1) Increased performance
(2) Increased responsiveness

Question 27

Explain why a thread is cheaper than a new process in context switching

Answer 27

Since threads share a process memory it is not required to reload memory maps, updating tables, lists eg. which results in it taking less CPU time and affects performance less negative

Question 28

What are some benefits of multithreading?

Answer 28

(1) Improved throughput
(2) Improved responsivenesss
(3) Performing complex computations

Question 29

What does “improved throughput” mean?

Answer 29

Eg. the processor will be idle waiting for IO operations taking time, one thread can take this job making better use of processor

Question 30

What does “improved responsiveness” mean?

Answer 30

eg. UI can be more responsive it certain parts (eg. IO calls) can be given to a thread

Question 31

What is the downside of multithreading?

Answer 31

• Resource expensive as a large number of thread takes a lot of memory, and take a lot of CPU time

Question 32

How can concurrency be implemented?

Answer 32

(1) Processes
(2) Threads