Subscriber.java

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/*
 * Software License Agreement (BSD License)
 *
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// author: Jason Wolfe



package ros;

import java.util.Queue;
import java.util.concurrent.ConcurrentLinkedQueue;

import ros.communication.Message;

public interface Subscriber<M extends Message> {
        public String getTopic();
        public void shutdown();
        public boolean isValid();
        
        public static interface Callback<M extends Message> {
                // request must be treated as constant, since it may be concurrently accessed by other threads..
                public void call(M request);
        }
        
        public static class QueueingCallback<M extends Message> implements Callback<M> {
                private Queue<M> queue;
                
                public QueueingCallback() {
                        queue = new ConcurrentLinkedQueue<M>();
                }
                
                @SuppressWarnings({ "unchecked"})
                public void call(M request) {
                        synchronized(queue) {
                                queue.add((M) request.clone());
                                queue.notify();
                        }
                }
                
                public M pop() throws InterruptedException {
                        synchronized(queue) {
                                while(queue.isEmpty()) {
                                        queue.wait();
                                }
                                return queue.remove();
                        }
                }
                

                public M peek() throws InterruptedException {
                        synchronized(queue) {
                                while(queue.isEmpty()) {
                                        queue.wait();
                                }
                                return queue.peek();
                        }
                }

                public void clear() {
                        synchronized(queue) {
                                queue.clear();
                        }
                }

                
                public boolean isEmpty() {
                        return queue.isEmpty();
                }
                
                public int     size() {
                        return queue.size();
                }
                
        }
}