Question

A semaphore is a useful synchronization primitive. Which of the following statements are true of semaphores?

a. Each semaphore has an integer value.
b. If a semaphore is initialized to 1, it can be used as a lock.
c. Semaphores can be initialized to values higher than 1.
d. Semaphore values can be negative in certain cases.
e. We have discussed the classic wait() and signal() semaphore operations. POSIX declares these operations sem_wait() and sem_post(), respectively. Thus, calling sem_post() may block, depending on the current value of the semaphore.

Answer 1

Semaphores are synchronization primitives with an integer value. They can act as locks when initialized to 1 and can handle multiple resources when set above 1. Semaphore values don't go negative, and sem_post() does not block.

Step-by-step explanation:

A semaphore is indeed a useful synchronization primitive in concurrent programming. Here are the clarifications for the statements provided:

• a. True. Each semaphore has an integer value which typically represents the number of resources available.
• b. True. If a semaphore is initialized to 1, it can act as a mutex lock, ensuring exclusive access to a resource.
• c. True. Semaphores can be initialized with values higher than 1, enabling control over access to multiple resources of the same type.
• d. True. Semaphore values can indirectly be negative if more processes are waiting than the number of resources available, though the actual counter does not go below zero.
• e. False. Calling sem_post() increments the semaphore's value and never blocks; it might wake up another thread if it is waiting.

It is important to understand how semaphores function as they play a critical role in avoiding race conditions and ensuring proper synchronization in multi-threaded applications.