X. 
   Mutual exclusion
   hold & wait
   no preemption
   cycle in resource request graph



4.

    examHandout = new Semaphore();
    examHandin = new Semaphore();
    studentReady = new Semaphore();
    testStart = new Condition(lock);
    testStop = new Condition(lock); 
     
    Student() {
        examHandout.P();
        println("writing name");
        studentReady.V();
        testStart.sleep();
        println("taking test");
        testStop.sleep();
        examHandin.V();
    }
    TA() {
        repeat 50 {
            examHandout.V();
        }
    }
     
    Professor() {
        repeat 100 {
            studentReady.P();
        }
     
        testStart.wakeAll();
        waitUntil(90*60);
        testStop.wakeAll();
          
        repeat 100 {
            examHandin.P();
        }