chapter 31: semaphores

Question 1

what are the 3 main things about a semaphore?

Answer 1

init counter variable, sem_wait() and sem_post()

Question 2

what does sem_post() do?

Answer 2

increment the variable, unblock a waiting thread if there are any

Question 3

what does sem_wait() do?

Answer 3

decrement the variable and block until semaphore is free

Question 4

what does the counter variable of the semaphore do?

Answer 4

when negative, it is equal to the number of waiting threads. although generally isn’t seen by the user.

Question 5

semaphore as locks (binary semaphore) and what should the initial value be?

Answer 5

sem_wait(&m)
CS
sem_post(&m)

sem_value = 1