1) With Hoare-style condition variables, a signaling thread immediately
blocks and does not resume until the signaled thread blocks or leaves the
monitor, whereas with Mesa-style condition variables, the signaled thread
is placed on the running queue (allowing the signaling thread to first
leave the monitor or block) or waits for another condition.  Although
Hoare-style variables provide for simpler proof rules, Mesa-style
variables are usually used in real operating systems.

4)
int xmit, rcv;

monitor Radar  {
       int state;
       condvar r;

       void transmit() {
               while(state == 1)
                      r.wait();
       }

       void receive()  {
               while(state == 0)
                       r.wait();
       }

       void release()  {
              state = (state + 1) % 2;
               r.signal();
       }

       void init()     {
               state = 0;
       }
}

void transmitter()     {
       while(1)        {
               Radar.transmit();
               // Transmit
               Radar.release();
       }
}

void receiver()        {
       while(1)        {
               Radar.receive();
               // Receive
               Radar.release();
       }
}

void main()    {
       xmit = thread_create(transmitter);
       rcv = thread_create(receiver);
       Radar.initRadar();
       thread_start(xmit);
       thread_start(rcv);
}

5)
monitor BouncerRobot    {
  int num_old, num_young, num_drinkers, num_smokers;
  condvar young, middle, old;

  int EnterRestaurant(int age, boolean wantToDrink, bool wantToSmoke)   {
        if(age < 40)    {
                while(num_drinkers > 0 || (wantToSmoke && num_old > 0))
                    young.wait();
                if(wantToSmoke)
                        num_smokers++;
                num_young++;
        } else if(age > 90)     {
                while(num_smokers > 0 || (wantToDrink && num_young > 0))
                        old.wait();
                if(wantToDrink)
                        num_drinkers++;
                num_old++;
        } else  {
                while((wantToSmoke && num_old > 0) || 
                      (wantToDrink && num_young > 0))
                        middle.wait();

                if(wantToSmoke)
                        num_smokers++;
                if(wantToDrink)
                        num_drinkers++;
        }
  }

  int ExitRestaurant(int age, boolean wasADrinker, boolean wasASmoker)  {
        if(age < 40)
                if(--num_young == 0) {
                     middle.broadcast();
                     old.broadcast();
                }
        if(age > 90)
                if(--num_old == 0) {
                     middle.broadcast();
                     young.broadcast();
                }                   
        if(wasASmoker) {
                if(--num_smokers == 0)
                     old.broadcast();
        }
        if(wasADrinker) {
                if(--num_drinkers == 0)
                     young.broadcast();
        }
  }