Process Synchronization

Question 1

Race Condition

Answer 1

Situation where several processes or threads manipulate shared data, and the outcome depends on the execution order

Question 2

To prevent race conditions, concurrent processes must be

Answer 2

synchronized

Question 3

Synchronized

Answer 3

Ensures that only one process at a time is manipulating the shared variable, operations must be performed atomically

Question 4

Atomic Operation

Answer 4

An operation without interruption

Question 5

Where are there significant race conditions?

Answer 5

I/O
Variable sharing

Question 6

Critical Section

Answer 6

Segment of code in which the process may be changing shared data

Question 7

Solution to critical section problem must satisfy 3 requirements

Answer 7

Mutual Exclusion
Progress
Bounded Waiting

Question 8

Mutual Exclusion

Answer 8

If a process is in its critical section then no other processes can be executing in their critical sections

Question 9

Progress

Answer 9

The decision of which process enters the critical section cannot be postponed indefinitely

Question 10

Bounded Waiting

Answer 10

There must be a limit on how many times other processes can enter their critical section after a process requests access

Question 11

We need _ from critical sections

Answer 11

Mutual Exclusion

Question 12

Disabling hardware interrupts CS problem

Answer 12

Works but not reasonable, not feasible due to the risk of indefinitely blocking other processes

Question 13

Simple lock variable CS problem

Answer 13

Suffers from race condition of setting the lock

Question 14

Indivisible lock variable CS problem

Answer 14

Works, uses Test and Set Lock (TSL) instruction to prevent race condition. Finds lock at 0 and sets it in one shot

Question 15

no-TSL toggle for two thread CS problem

Answer 15

Doesnt have progress, if B is faster than A, will lock itself out of CS. Tries to take turns but doesnt work if one process should enter multiple times before other

Question 16

Petersons no-tsl, no alternation CS problem

Answer 16

idk

Question 17

Busy waiting

Answer 17

Means the process/thread continuously execute a tight loop until some condition changes

Question 18

Why is busy waiting bad?

Answer 18

Waste of CPU time
Paradox of inversed priority

Question 19

Busy waiting basic solution

Answer 19

Waiting process needs to block, not keep idling

Question 20

Semaphores

Answer 20

Semaphore S can be accessed by two operations
wait()/P(), and signal()/V()

Question 21

Counting semaphore

Answer 21

Integer value can range over an unrestricted domain

Question 22

Binary Semaphore

Answer 22

Integer value can range only between 0 and 1 aka mutex locks