utils/misc/src/main/java/org/onlab/util/Timer.java

/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you 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 org.onlab.util;

import org.jboss.netty.util.HashedWheelTimer;

/**
 * Hashed-wheel timer singleton. Care must be taken to shutdown the timer
 * only when the VM is ready to exit.
 */
public final class Timer {

    private static volatile HashedWheelTimer timer;

    // Ban public construction
    private Timer() {
    }

    /**
     * Returns the singleton hashed-wheel timer.
     *
     * @return hashed-wheel timer
     */
    public static HashedWheelTimer getTimer() {
        if (Timer.timer == null) {
            initTimer();
        }
        return Timer.timer;
    }

    private static synchronized  void initTimer() {
        if (Timer.timer == null) {
            HashedWheelTimer hwTimer = new HashedWheelTimer();
            hwTimer.start();
            Timer.timer = hwTimer;
        }
    }

}