🚀 go-pugleaf

Hi all,
This is a longish post, so I must apologise. What I am trying to do is to
simulate a Semaphore. For some reason the implementation seems to enter into
a deadlocked state. Could anyone help in finding out why? TeamB?

8<--------------------Semaphore.java------------------------------
/**
 * Implementation of the synchronisation primitive
 * commonly known as a Semaphore.
 */
public class Semaphore{
    int _initialCount;//the max no. of resources this semaphore
                      // is guarding.
                      // In other words - the max no of threads
                      // that have performed the down() op and
                      // are still in the running state.

    int _freeCount;// the no. of times down()can be performed
                   //  without suspending the calling thread.

    Object _waitObject;

    public Semaphore(int count){
        if(count == 0)
            throw new IllegalArgumentException("parameter cannot be zero");
        _initialCount = count;
        _freeCount = _initialCount;
        _waitObject = new WaitObject();
    }

    public synchronized void down(){
        --_freeCount;
        if( _freeCount < 0 ){
            _freeCount = 0;


{ 
                synchronized(_waitObject){
                    _waitObject.wait();
                }
            }catch(Exception e){
                System.out.println("Exception:");
                e.printStackTrace();
            }
        }
    }
    
    public synchronized void up(){
        ++_freeCount;
        if(_freeCount > _initialCount)
            _freeCount = _initialCount;
        synchronized(_waitObject){
            _waitObject.notify();
        }
    }
    
    
    public static void test(){
        Semaphore s = new Semaphore(1);
        
        Thread t1 = new TestThread(s,1);
        Thread t2 = new TestThread(s,2);
        Thread t3 = new TestThread(s,3);
        t1.start();
        t2.start();
        t3.start();
       
 for(int i = 0;i<1000;++i);
        Thread.yield();
        Thread.yield();
        Thread.yield();
        try{
            Thread.sleep(200000000L);
        }catch(Exception e){};
    }

    public static void main(String[] a){
        Semaphore.test();
    }
}

class WaitObject{}

class TestThread extends Thread{
    Semaphore _s;
    int _id;
    public TestThread(Semaphore s, int id){
        _s = s;
        _id = id;
    }

    public void run(){
        System.out.println("Before down : " + _id);
        _s.down();
        yield();
        System.out.println("1st After down : " + _id);
        yield();
        System.out.println("2nd After down : " + _id);
        yield();
        System.out.println("3rd After down : " + _id);
        yield();
        System.out.println("4th After down : " + _id);
        _s.up();
    }
}

8<--------------------------------------------------------------------------
--------

I think that the notifies are getting lost somewhere. Is that correct?


Many thanks
-MM