Chapter 23

Question 1

What is semaphore

Answer 1

Semaphore is an integer variable that can be accessed by 2 atomic operations.

Question 2

What block() operation do

Answer 2

block() suspends the process that invokes it

Question 3

What wakeup() operation do

Answer 3

wakeup(P) resumes the execution of a blocked process P.

Question 4

When critical sections are small which one is better

• busy-waiting
• queue-waiting

Answer 4

busy-waiting

Question 5

When critical sections are long which one is better

• busy-waiting
• queue-waiting

Answer 5

queue-waiting

Question 6

Could we have semaphorse based solution for process synchronization

Answer 6

Yes

Question 7

If programmer mistakenly use semaphore wait operation, what will happen

Answer 7

Then there will be 3 general problems

1. Mutual exclusion violation
2. Infinite blocking of some process (starvation)
3. Deadlocks (2 processes waiting for each other to execute and no one execute)

Question 8

What are 2 types of deadlock

Answer 8

1. Traffic deadlock

2. one-way bridge-crossing

Question 9

Why programming error occurs in semaphore

Answer 9

Due to tandem use of wait() and signal() operations

Question 10

What is the solution of programming errors in semaphore

Answer 10

Make wait() and signal() operations as programming construct. Then programmer do not need to implement it.

Question 11

What are 2 examples of programming constructs for semaphor

Answer 11

1. Critical regions

2. Monitors

Question 12

What are types of semaphores

Answer 12

1. Counting semaphore

2. Binary semaphore

Question 13

What are binary semaphore

Answer 13

Its integer value can not be >1. They are simpler to implement. Values can be negative.

Question 14

What are counting semaphore

Answer 14

Integer value can range over an unrestricted integer domain.