samples.websocket.jetty.snake.SnakeTimer.java Source code

Introduction

Here is the source code for samples.websocket.jetty.snake.SnakeTimer.java

Source

/*
 * Copyright 2012-2018 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package samples.websocket.jetty.snake;

import java.util.Collection;
import java.util.Collections;
import java.util.Iterator;
import java.util.Timer;
import java.util.TimerTask;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.CopyOnWriteArrayList;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;

/**
 * Sets up the timer for the multi-player snake game WebSocket example.
 */
public final class SnakeTimer {

    private static final long TICK_DELAY = 100;

    private static final Object MONITOR = new Object();

    private static final Log logger = LogFactory.getLog(SnakeTimer.class);

    private static final ConcurrentHashMap<Integer, Snake> snakes = new ConcurrentHashMap<>();

    private static Timer gameTimer = null;

    private SnakeTimer() {
    }

    public static void addSnake(Snake snake) {
        synchronized (MONITOR) {
            if (snakes.isEmpty()) {
                startTimer();
            }
            snakes.put(Integer.valueOf(snake.getId()), snake);
        }
    }

    public static Collection<Snake> getSnakes() {
        return Collections.unmodifiableCollection(snakes.values());
    }

    public static void removeSnake(Snake snake) {
        synchronized (MONITOR) {
            snakes.remove(Integer.valueOf(snake.getId()));
            if (snakes.isEmpty()) {
                stopTimer();
            }
        }
    }

    public static void tick() throws Exception {
        StringBuilder sb = new StringBuilder();
        for (Iterator<Snake> iterator = SnakeTimer.getSnakes().iterator(); iterator.hasNext();) {
            Snake snake = iterator.next();
            snake.update(SnakeTimer.getSnakes());
            sb.append(snake.getLocationsJson());
            if (iterator.hasNext()) {
                sb.append(',');
            }
        }
        broadcast(String.format("{'type': 'update', 'data' : [%s]}", sb.toString()));
    }

    public static void broadcast(String message) throws Exception {
        Collection<Snake> snakes = new CopyOnWriteArrayList<>(SnakeTimer.getSnakes());
        for (Snake snake : snakes) {
            try {
                snake.sendMessage(message);
            } catch (Throwable ex) {
                // if Snake#sendMessage fails the client is removed
                removeSnake(snake);
            }
        }
    }

    public static void startTimer() {
        gameTimer = new Timer(SnakeTimer.class.getSimpleName() + " Timer");
        gameTimer.scheduleAtFixedRate(new TimerTask() {
            @Override
            public void run() {
                try {
                    tick();
                } catch (Throwable ex) {
                    logger.error("Caught to prevent timer from shutting down", ex);
                }
            }
        }, TICK_DELAY, TICK_DELAY);
    }

    public static void stopTimer() {
        if (gameTimer != null) {
            gameTimer.cancel();
        }
    }

}