G52CON: Exercise 4, Java

A semaphore s is an integer variable which can take only non-negative values. Once it has been given its initial value, the only permissible operations on s are the atomic actions:

• P(s) : if s > 0 then s = s - 1, else suspend execution of the process that called P(s)
• V(s) : if some process p is suspended by a previous P(s) on this semaphore then resume p, else s = s + 1

(a) Using the skeleton below, give a definition of a Java class GeneralSemaphore that implements a general semaphore. The class should have two methods P() and V() that implement the corresponding semaphore operations.

class GeneralSemaphore {
    private long resource;

    public GeneralSemaphore (long r) {
        resource = r;
    }

    // method to implement the P operation

    // method to implement the V operation
}