import java.util.LinkedList;
import java.util.concurrent.ConcurrentHashMap;

class Session {
		static public ConcurrentHashMap<String, Session> sessions = 
			new ConcurrentHashMap<String, Session>();

		LinkedList<String> msg = new LinkedList<String>();
		
		public static Session get(String s) {
			Session t = sessions.get(s);
			if (t==null) {
				t = new Session();
				sessions.put(s, t);
			}
			return t;
		}

		public String handlePush() {
			synchronized (msg) {
				if (msg.isEmpty()) {
					try {
						msg.wait();					
					} catch (InterruptedException e) {
						e.printStackTrace();
					}		
				}
				return msg.poll();
			}
		}
		
	}