A multithreaded queue used for implementing producer-consumer style threading patterns
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import java.util.Stack;
/**
* A multithreaded queue used for
* implementing producer-consumer style threading patterns.
* Multiple threads can wait for runnable objects being added
* to the queue while other threads add to the queue.
*/
public class Queue {
private Stack tasks = new Stack();
private long defaultTimeout = 100;
public Queue() {
}
/**
* Returns the current number of runnable objects in the queue
*/
public synchronized int size() {
return tasks.size();
}
/**
* adds a runnable object to the end of the queue.
* At least one thread will be notified.
*/
public synchronized void add(Object runnable) {
tasks.push(runnable);
notifyAll();
}
/**
* Removes the first runnable object from the queue, blocking until one is available.
*/
public synchronized Object remove() {
while (true) {
Object runnable = removeNoWait();
if ( runnable != null ) {
return runnable;
}
try {
wait( defaultTimeout );
}
catch (InterruptedException e) {
e.printStackTrace();
}
}
}
/**
* Removes the first runnable object from the queue without blocking.
* This method will return immediately with an item from the queue or null.
* @return the first runnable object removed from the queue or null if the
* queue is empty
*/
public synchronized Object removeNoWait() {
if ( ! tasks.empty() ) {
return tasks.pop();
} else {
return null;
}
}
}
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