Question

Is the following operation of semaphore correct, please explain.

signal (mutex) …. wait (mutex)  

Note:

wait (S) {

    while (S <= 0)

       ; // busy wait

    S--;

}

signal (S) {

    S++;

}

Answer 1

Yes, the given operation of the semaphore is correct.

Explanation:

Semaphore:

A semaphore is a simple and special variable and it solves the critical section problem that can be accessed by only two system calls signal() and wait() which are atomic in nature.

The given code is for counting semaphore and it has unrestricted domain.

The translated code using V() is given below:

signal(S)
{
S++;
}

The translated code using P() is given below:

wait(S)
{
while(S<=0);
S--;
}

The wait() operation is the waits operation and it waits until the variable 'S' is less than or equal to 0. The while() loop is terminated by semicolon means it will be executed while the condition is true. If no resource is available the busy-waiting state will occur.

The signal() operation increments the value by one.