objectfifo.java

Java Thread Programming (Source

public class ObjectFIFO extends Object {
	private Object[] queue;
	private int capacity;
	private int size;
	private int head;
	private int tail;

	public ObjectFIFO(int cap) {
		capacity = ( cap > 0 ) ? cap : 1; // at least 1
		queue = new Object[capacity];
		head = 0;
		tail = 0;
		size = 0;
	}

	public int getCapacity() {
		return capacity;
	}

	public synchronized int getSize() {
		return size;
	}

	public synchronized boolean isEmpty() {
		return ( size == 0 );
	}

	public synchronized boolean isFull() {
		return ( size == capacity );
	}

	public synchronized void add(Object obj) 
			throws InterruptedException {

		waitWhileFull();

		queue[head] = obj;
		head = ( head + 1 ) % capacity;
		size++;

		notifyAll(); // let any waiting threads know about change
	}

	public synchronized void addEach(Object[] list) 
			throws InterruptedException {

		//
		// You might want to code a more efficient 
		// implementation here ... (see ByteFIFO.java)
		//

		for ( int i = 0; i < list.length; i++ ) {
			add(list[i]);
		}
	}

	public synchronized Object remove() 
			throws InterruptedException {

		waitWhileEmpty();
		
		Object obj = queue[tail];

		// don't block GC by keeping unnecessary reference
		queue[tail] = null; 

		tail = ( tail + 1 ) % capacity;
		size--;

		notifyAll(); // let any waiting threads know about change

		return obj;
	}

	public synchronized Object[] removeAll() 
			throws InterruptedException {

		//
		// You might want to code a more efficient 
		// implementation here ... (see ByteFIFO.java)
		//

		Object[] list = new Object[size]; // use the current size

		for ( int i = 0; i < list.length; i++ ) {
			list[i] = remove();
		}

		// if FIFO was empty, a zero-length array is returned
		return list; 
	}

	public synchronized Object[] removeAtLeastOne() 
			throws InterruptedException {

		waitWhileEmpty(); // wait for a least one to be in FIFO
		return removeAll();
	}

	public synchronized boolean waitUntilEmpty(long msTimeout) 
			throws InterruptedException {

		if ( msTimeout == 0L ) {
			waitUntilEmpty();  // use other method
			return true;
		}

		// wait only for the specified amount of time
		long endTime = System.currentTimeMillis() + msTimeout;
		long msRemaining = msTimeout;

		while ( !isEmpty() && ( msRemaining > 0L ) ) {
			wait(msRemaining);
			msRemaining = endTime - System.currentTimeMillis();
		}

		// May have timed out, or may have met condition, 
		// calc return value.
		return isEmpty();
	}

	public synchronized void waitUntilEmpty() 
			throws InterruptedException {

		while ( !isEmpty() ) {
			wait();
		}
	}

	public synchronized void waitWhileEmpty() 
			throws InterruptedException {

		while ( isEmpty() ) {
			wait();
		}
	}

	public synchronized void waitUntilFull() 
			throws InterruptedException {

		while ( !isFull() ) {
			wait();
		}
	}

	public synchronized void waitWhileFull() 
			throws InterruptedException {

		while ( isFull() ) {
			wait();
		}
	}
}