src/java.management/share/classes/sun/management/Sensor.java

/*
 * Copyright (c) 2003, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Oracle in the LICENSE file that accompanied this code.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
 * or visit www.oracle.com if you need additional information or have any
 * questions.
 */

package sun.management;

import java.lang.management.MemoryUsage;
import java.util.Iterator;
import java.util.Map;
import java.util.HashMap;

/**
 * An abstract sensor.
 *
 * <p>
 * An {@code AbstractSensor} object consists of two attributes:
 * <ul>
 *   <li>{@code on} is a boolean flag indicating if a sensor is
 *       triggered. This flag will be set or cleared by the
 *       component that owns the sensor.</li>
 *   <li>{@code count} is the total number of times that a sensor
 *       has been triggered.</li>
 * </ul>
 *
 * @author  Mandy Chung
 * @since   1.5
 */

public abstract class Sensor {
    private final Object lock = new Object();
    private final String name;
    private long count;                 // VM-initialized to 0
    private boolean on;                 // VM-initialized to false

    /**
     * Constructs a {@code Sensor} object.
     *
     * @param name The name of this sensor.
     */
    public Sensor(String name) {
        this.name = name;
    }

    /**
     * Returns the name of this sensor.
     *
     * @return the name of this sensor.
     */
    public String getName() {
        return name;
    }

    /**
     * Returns the total number of times that this sensor has been triggered.
     *
     * @return the total number of times that this sensor has been triggered.
     */
    public long getCount() {
        synchronized (lock) {
            return count;
        }
    }

    /**
     * Tests if this sensor is currently on.
     *
     * @return {@code true} if the sensor is currently on;
     *         {@code false} otherwise.
     *
     */
    public boolean isOn() {
        synchronized (lock) {
            return on;
        }
    }

    /**
     * Triggers this sensor. This method first sets this sensor on
     * and increments its sensor count.
     */
    public void trigger() {
        synchronized (lock) {
            on = true;
            count++;
        }
        triggerAction();
    }

    /**
     * Triggers this sensor. This method sets this sensor on
     * and increments the count with the input {@code increment}.
     */
    public void trigger(int increment) {
        synchronized (lock) {
            on = true;
            count += increment;
            // Do something here...
        }
        triggerAction();
    }

    /**
     * Triggers this sensor piggybacking a memory usage object.
     * This method sets this sensor on
     * and increments the count with the input {@code increment}.
     */
    public void trigger(int increment, MemoryUsage usage) {
        synchronized (lock) {
            on = true;
            count += increment;
            // Do something here...
        }
        triggerAction(usage);
    }

    /**
     * Clears this sensor.
     */
    public void clear() {
        synchronized (lock) {
            on = false;
        }
        clearAction();
    }


    /**
     * Clears this sensor
     * and increments the count with the input {@code increment}.
     */
    public void clear(int increment) {
        synchronized (lock) {
            on = false;
            count += increment;
        }
        clearAction();
    }

    public String toString() {
        return "Sensor - " + getName() +
            (isOn() ? " on " : " off ") +
            " count = " + getCount();
    }

    abstract void triggerAction();
    abstract void triggerAction(MemoryUsage u);
    abstract void clearAction();
}