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package horstmann.ch09_queue2;
import java.util.ArrayList;
import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;
/**
A first-in, first-out bounded collection of objects.
*/
public class BoundedQueue<E>
{
/**
Constructs an empty queue.
@param capacity the maximum capacity of the queue
*/
public BoundedQueue(int capacity)
{
elements = new ArrayList<E>(capacity);
head = 0;
tail = 0;
size = 0;
}
/**
Removes the object at the head.
@return the object that has been removed from the queue
*/
public E remove() throws InterruptedException
{
queueLock.lock();
try
{
while (size == 0)
valueAvailableCondition.await();
E r = elements.get(head);
head++;
size--;
if (head == elements.size())
head = 0;
spaceAvailableCondition.signalAll();
return r;
}
finally
{
queueLock.unlock();
}
}
/**
Appends an object at the tail.
@param newValue the object to be appended
*/
public void add(E newValue) throws InterruptedException
{
queueLock.lock();
try
{
while (size == elements.size())
spaceAvailableCondition.await();
elements.set(tail,newValue);
tail++;
size++;
if (tail == elements.size())
tail = 0;
valueAvailableCondition.signalAll();
}
finally
{
queueLock.unlock();
}
}
private ArrayList<E> elements;
private int head;
private int tail;
private int size;
private Lock queueLock = new ReentrantLock();
private Condition spaceAvailableCondition
= queueLock.newCondition();
private Condition valueAvailableCondition
= queueLock.newCondition();
}
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