ActiveMQ example source code file (Valve.java)

This example ActiveMQ source code file (Valve.java) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" ^TM.

Java - ActiveMQ tags/keywords

illegalstateexception, illegalstateexception, interruptedexception, interruptedexception, object, object, unbalanced, unbalanced, valve

The ActiveMQ Valve.java source code

/**
 * 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.apache.activemq.thread;

/**
 * A Valve is a synchronization object used enable or disable the "flow" of
 * concurrent processing.
 * 
 * 
 */
public final class Valve {

    private final Object mutex = new Object();
    private boolean on;
    private int turningOff;
    private int usage;

    public Valve(boolean on) {
        this.on = on;
    }

    /**
     * Turns the valve on. This method blocks until the valve is off.
     * 
     * @throws InterruptedException if wait is interrupted
     */
    public void turnOn() throws InterruptedException {
        synchronized (mutex) {
            while (on) {
                mutex.wait();
            }
            on = true;
            mutex.notifyAll();
        }
    }

    public boolean isOn() {
        synchronized (mutex) {
            return on;
        }
    }

    /**
     * Turns the valve off. This method blocks until the valve is on and the
     * valve is not in use.
     * 
     * @throws InterruptedException if wait is interrupted
     */
    public void turnOff() throws InterruptedException {
        synchronized (mutex) {
            if (turningOff < 0) {
                throw new IllegalStateException("Unbalanced turningOff: " + turningOff);
            }
            try {
                ++turningOff;
                while (usage > 0 || !on) {
                    mutex.wait();
                }
                on = false;
                mutex.notifyAll();
            } finally {
                --turningOff;
            }
        }
    }

    /**
     * Increments the use counter of the valve. This method blocks if the valve
     * is off, or is being turned off.
     * 
     * @throws InterruptedException  if wait is interrupted
     */
    public void increment() throws InterruptedException {
        synchronized (mutex) {
            if (turningOff < 0) {
                throw new IllegalStateException("Unbalanced turningOff: " + turningOff);
            }
            if (usage < 0) {
                throw new IllegalStateException("Unbalanced usage: " + usage);
            }
            // Do we have to wait for the value to be on?
            while (turningOff > 0 || !on) {
                mutex.wait();
            }
            usage++;
        }
    }

    /**
     * Decrements the use counter of the valve.
     */
    public void decrement() {
        synchronized (mutex) {
            usage--;
            if (turningOff < 0) {
                throw new IllegalStateException("Unbalanced turningOff: " + turningOff);
            }
            if (usage < 0) {
                throw new IllegalStateException("Unbalanced usage: " + usage);
            }
            if (turningOff > 0 && usage < 1) {
                mutex.notifyAll();
            }
        }
    }

}