memoryutils.java

非常棒的java数据库

/*
 * Copyright 2004-2008 H2 Group. Licensed under the H2 License, Version 1.0
 * (http://h2database.com/html/license.html).
 * Initial Developer: H2 Group
 */
package org.h2.util;

/**
 * This is a utility class with functions to measure the free and used memory.
 */
public class MemoryUtils {

    private static long lastGC;
    private static final int GC_DELAY = 50;
    private static final int MAX_GC = 8;

    /**
     * Get the used memory in KB.
     *
     * @return the used memory
     */
    public static int getMemoryUsed() {
        collectGarbage();
        Runtime rt = Runtime.getRuntime();
        long mem = rt.totalMemory() - rt.freeMemory();
        return (int) (mem >> 10);
    }

    /**
     * Get the free memory in KB.
     *
     * @return the used memory
     */
    public static int getMemoryFree() {
        collectGarbage();
        Runtime rt = Runtime.getRuntime();
        long mem = rt.freeMemory();
        return (int) (mem >> 10);
    }

    private static synchronized void collectGarbage() {
        Runtime runtime = Runtime.getRuntime();
        long total = runtime.totalMemory();
        long time = System.currentTimeMillis();
        if (lastGC + GC_DELAY < time) {
            for (int i = 0; i < MAX_GC; i++) {
                runtime.gc();
                long now = runtime.totalMemory();
                if (now == total) {
                    lastGC = System.currentTimeMillis();
                    break;
                }
                total = now;
            }
        }
    }

}