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package org.apache.tomcat.util.collections;
import java.util.Vector;
/**
* A simple FIFO queue class which causes the calling thread to wait
* if the queue is empty and notifies threads that are waiting when it
* is not empty.
*
* @author Anil V ([email protected])
*/
public class Queue {
private Vector vector = new Vector();
private boolean stopWaiting=false;
private boolean waiting=false;
/**
* Put the object into the queue.
*
* @param object the object to be appended to the
* queue.
*/
public synchronized void put(Object object) {
vector.addElement(object);
notify();
}
/** Break the pull(), allowing the calling thread to exit
*/
public synchronized void stop() {
stopWaiting=true;
// just a hack to stop waiting
if( waiting ) notify();
}
/**
* Pull the first object out of the queue. Wait if the queue is
* empty.
*/
public synchronized Object pull() {
while (isEmpty()) {
try {
waiting=true;
wait();
} catch (InterruptedException ex) {
}
waiting=false;
if( stopWaiting ) return null;
}
return get();
}
/**
* Get the first object out of the queue. Return null if the queue
* is empty.
*/
public synchronized Object get() {
Object object = peek();
if (object != null)
vector.removeElementAt(0);
return object;
}
/**
* Peek to see if something is available.
*/
public Object peek() {
if (isEmpty())
return null;
return vector.elementAt(0);
}
/**
* Is the queue empty?
*/
public boolean isEmpty() {
return vector.isEmpty();
}
/**
* How many elements are there in this queue?
*/
public int size() {
return vector.size();
}
}