package UK.co.demon.xinit.utility;

/* 
 * NAME	  : Fifo  - a thread safe fifo implementation.  
 *
 * NOTES   : This Fifo example is shamelessly taken from 
 *           "Concurrent Programming in Java" by Doug Lea. 
 *           Only the names have been simplified. Read the 
 *	     book, it's well worth the effort
 */ 

public 
class Fifo 
{
    private FIFOnode head_;
    private FIFOnode last_;
    private Object lockOnLast_;

    public 
    Fifo()
    {
	head_ = last_ = new Fifo(null, null);
	lockOnLast_ = new Object();
    }

    public
    void
    put(Object x)
    {
	Fifo newNode = new Fifo(x, null);

	synchronized (lockOnLast_)
	{
	    last_.next = newNode;
	    last_ = newNode;
	}

    }

    public
    synchronized
    Object
    take(Object x)
    {
	Object x = null;

	Fifo first = head_.next;

	if (first != null)
	{
	    x = first.value;
	    head_ = first;
	}

	return x;
    }
}

final
class
FIFOnode
{
    Object value;
    FIFOnode next;

    FIFOnode(Object x, FIFOnode n)
    {
	value = x;
	next = n;
    }
}

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