Concurrency

Question 1

What’s the main difference between threads and processes?

Answer 1

Threads of the same process share the same address space

Question 2

Allowing multiple threads within the same process to share the same address space allows the threads to be…

Answer 2

independent of each other

Question 3

What do the threads within a process share?

Answer 3

Process ID
Address space
Open files
Other resources

Question 4

What does each thread within a process have, that it doesn’t share?

Answer 4

Thread ID
Set of registers - including PC
Stack

Question 5

Give the definition:
A thread based on the POSIX library where an API specifies the behaviour of its library

Answer 5

POSIX thread - Pthread

Question 6

What sort of results can concurrency lead to?

Answer 6

Non-deterministic results - different results despite the same input

Question 7

⭐️ Give the definition:
When multiple threads of execution update the shared data structure, and the final result depends on the execution order

Answer 7

Race condition

Question 8

⭐️ Give the definition:
An operation that completes in its entirety without worrying about interruption by any other potentially conflict-causing threads

Answer 8

Atomic operation

Question 9

⭐️ What do we call the problem that is to ensure that when one thread is executing in its critical section, no other thread is allowed to execute in that critical section?

Answer 9

The critical section problem

Question 10

⭐️ Give the definition:
A piece of code that accesses a shared resource, usually a variable or data structure

Answer 10

Critical section

Question 11

⭐️ What are the three parts of the solution to the critical section problem?

Answer 11

1. Mutual exclusion
2. Progress
3. Bounded

Question 12

⭐️ Give the definition:
A part of the solution to the critical section problem where only one thread is allowed in the critical section at a time

Answer 12

Mutual exclusion

Question 13

⭐️ Give the definition:
The part of the solution to the critical section problem that ensures that no deadlock occurs; where if there are several simultaneous requests from threads, one must be allowed to proceed

Answer 13

Progress

Question 14

⭐️ Give the definition:
The part of the solution to the critical section problem that ensures that no starvation happens; where one must eventually allow each waiting thread to enter

Answer 14

Bounded

Question 15

⭐️ What are the 3 concurrency problems?

Answer 15

1. Race conditions
2. Critical section problem
3. Deadlocks

Question 16

⭐️ Give the definition:
Threads waiting forever for each other to release resources

Answer 16

Deadlock

Question 17

⭐️ What 3 techniques can be used to solve the concurrency problems?

Answer 17

1. Locks (mutexes)
2. Condition variables
3. Atomic operations

Question 18

⭐️ Give the definition:
Mutual exclusion primitives to protect critical sections. Only one thread can hold them at once.

Answer 18

Lock

Question 19

⭐️ Give the definition: allow threads to wait for certain conditions to be true

Answer 19

Condition variables

Question 20

⭐️ A critical section is a piece of code in a process / thread that accesses shared data (T/F)

Answer 20

True

Question 21

⭐️ What is a race condition?
1. A mechanism to ensure mutual exclusion in critical sections.
2. A type of deadlock where threads are waiting indefinitely
3. A synchronisation primitive used to lock resources
4. Two or more threads accessing shared data, lading to unpredictable results

Answer 21

4

Question 22

⭐️ What are the 3 requirements for a solution to the critical-section problem?

Answer 22

Mutual Exclusion, Progress, Bounded Waiting