trunk/activemq-core/src/main/java/org/apache/activemq/usage/MemoryUsage.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.apache.activemq.usage;

/**
 * Used to keep track of how much of something is being used so that a
 * productive working set usage can be controlled. Main use case is manage
 * memory usage.
 * 
 * @org.apache.xbean.XBean
 * 
 */
public class MemoryUsage extends Usage<MemoryUsage> {

    private long usage;

    public MemoryUsage() {
        this(null, null);
    }

    /**
     * Create the memory manager linked to a parent. When the memory manager is
     * linked to a parent then when usage increased or decreased, the parent's
     * usage is also increased or decreased.
     * 
     * @param parent
     */
    public MemoryUsage(MemoryUsage parent) {
        this(parent, "default");
    }

    public MemoryUsage(String name) {
        this(null, name);
    }

    public MemoryUsage(MemoryUsage parent, String name) {
        this(parent, name, 1.0f);
    }

    public MemoryUsage(MemoryUsage parent, String name, float portion) {
        super(parent, name, portion);
    }

    /**
     * @throws InterruptedException
     */
    public void waitForSpace() throws InterruptedException {
        if (parent != null) {
            parent.waitForSpace();
        }
        synchronized (usageMutex) {
            for (int i = 0; percentUsage >= 100; i++) {
                usageMutex.wait();
            }
        }
    }

    /**
     * @param timeout
     * @throws InterruptedException
     * @return true if space
     */
    public boolean waitForSpace(long timeout) throws InterruptedException {
        if (parent != null) {
            if (!parent.waitForSpace(timeout)) {
                return false;
            }
        }
        synchronized (usageMutex) {
            if (percentUsage >= 100) {
                usageMutex.wait(timeout);
            }
            return percentUsage < 100;
        }
    }

    public boolean isFull() {
        if (parent != null && parent.isFull()) {
            return true;
        }
        synchronized (usageMutex) {
            return percentUsage >= 100;
        }
    }

    /**
     * Tries to increase the usage by value amount but blocks if this object is
     * currently full.
     * 
     * @param value
     * @throws InterruptedException
     */
    public void enqueueUsage(long value) throws InterruptedException {
        waitForSpace();
        increaseUsage(value);
    }

    /**
     * Increases the usage by the value amount.
     * 
     * @param value
     */
    public void increaseUsage(long value) {
        if (value == 0) {
            return;
        }
        int percentUsage;
        synchronized (usageMutex) {
            usage += value;
            percentUsage = caclPercentUsage();
        }
        setPercentUsage(percentUsage);
        if (parent != null) {
            ((MemoryUsage)parent).increaseUsage(value);
        }
    }

    /**
     * Decreases the usage by the value amount.
     * 
     * @param value
     */
    public void decreaseUsage(long value) {
        if (value == 0) {
            return;
        }
        int percentUsage;
        synchronized (usageMutex) {
            usage -= value;
            percentUsage = caclPercentUsage();
        }
        setPercentUsage(percentUsage);
        if (parent != null) {
            parent.decreaseUsage(value);
        }
    }

    protected long retrieveUsage() {
        return usage;
    }

    public long getUsage() {
        return usage;
    }

    public void setUsage(long usage) {
        this.usage = usage;
    }
}