利用 Runtime 监控 Java 系统资源

这些日子要用爪哇语言(Java)做内存数据中心。于是把用 Java 监控运行环境硬件资源的内容复习了一下。爪哇类库提供了 java.util.Runtim 类,主要负责调用爪哇虚拟机(JavaVM)外部的基层操作系统功能、处理基于一种叫钩子的原理的程序、获取系统资源信息以及控制调试信息生成。本文单独利用其获取系统资源信息的功能。

java.util.Runtim 类具有以下几个方法和获取系统资源信息有关。以下代码可不是简简单单从标准类库里边复制出来的哦。全球目前独此一份。
/**
 * 返回爪哇(Java)虚拟机可用线程数。
 *
 * 

该值在特定的虚拟机调用期间可能发生更改。因此,对可用处理器数目很敏感的 * 应用程序应该不定期地轮询该属性,并相应地调整其资源用法。

* * @return 虚拟机可用的最大处理器数目;从不小于 1 * @since 1.4 */ public native int availableProcessors(); /** * 返回爪哇(Java)虚拟机中的空闲内存量。调用 gc 方法可能导致 * freeMemory 返回值的增加。 * * @return 供将来分配对象使用的当前可用内存的近似总量,以字节为单位。 */ public native long freeMemory(); /** * 返回爪哇(Java)虚拟机中的内存总量。此方法返回的值可能随时间的推移而变化,这 * 取决于主机环境。 *

* 注意,保存一个给定类型的对象所需的内存量可能取决于实现方式。 * * @return 目前为当前和后续对象提供的内存总量,以字节为单位。 */ public native long totalMemory(); // // /** * 返回爪哇(Java)虚拟机能够尝试使用的最大内存量。如果内存本身没有限制,则 * 返回值 {@link java.lang.Long#MAX_VALUE} 。

* * @return 虚拟机能够尝试使用的最大内存量,以字节为单位。 * @since 1.4 */ public native long maxMemory(); /** * 运行垃圾回收器。 * 调用此方法意味着爪哇(Java)虚拟机做了一些努力来回收未用对象,以便能够快速地 * 重用这些对象当前占用的内存。当控制从方法调用中返回时,虚拟机已经尽最大努力回收 * 了所有丢弃的对象。 *

* 名称 gc 代表“垃圾回收器”。虚拟机根据需要在单独的线程中自动执行 * 回收过程,甚至不用显式调用 gc 方法。 *

* 方法 {@link System#gc()} 是调用此方法的一种传统而便捷的方式 */ public native void gc();


我们可以看到这些都是本地方法。这意味着将 Runtime 对象远程传递之后,将不能得到正确执行结果。
这些方法用起来都很简单,文档注释也写得比较明白。
在高可用数据中心中,我认为应该 根据可用 CPU 线数决定程序开启的线程数。此线程数为 CPU 可用线数的某倍数。此倍数应通过实际经验所得。然后程序通过监控 CPU 可用线数,来控制线程池保留数量。
内存的控制,我想应该是在 内存超出警戒线时发出警报,以向运营人员申请增加内存数据中心服务器。同时,应该 在内存过满之前,由程序执行垃圾回收,以消除并无引用的老生代对象。
如果各位有对内存数据中心的想法、建议或者质疑,欢迎来一起讨论。

下边是我编写的一个系统资源测试程序。程序里边使用了 Runtime 类关于系统资源的所有方法。
package cn.spads.test.grammar;

import java.util.LinkedList;
import java.util.Random;

/**
 * 本类用于示范使用 Runtime 检查系统运行情况。
 * 将 Runtime 作为可变成员,是为多系统公用检查预留的设计。
 * @author	Shane Loo Li
 */
public class PerformanceMonitor
{
	/**
	 * 此量控制程序运行时间。此值越大,此演示程序运行时间越长。
	 */
	static public int runLoopTimes = 55;

	/**
	 * 此为每次检测间隔的时间片数。此值越大,间隔时间越长。
	 */
	static public int waitTime = 1500000;

	static public void main(String[] arguments) throws Exception
	{
		Runtime context = Runtime.getRuntime();
		final PerformanceMonitor monitor = new PerformanceMonitor(context);
		final LinkedList pretendedMemory = new LinkedList();
		new Thread(
				new Runnable()
				{
					public void run()
					{
						for (int j = -1; ++j != runLoopTimes; )
						{
							// 检查系统情况
							monitor.checkAll();

							// 每次检查运行情况之后,都会休息 1000 个时间片
							for (int i = -1; ++i != waitTime; ) Thread.yield();

							// 每次检查之后,会制造一些对象,记录其中一部分,并删除些老对象
							for (int i = -1; ++i != 20000; )
							{
								StringBuilder builder = new StringBuilder();
								Random ran = new Random();
								for (int index = -1; ++index != 100; )
									builder.append((char) (ran.nextInt(26) + 64));
								String garbage = new String(builder.toString());
								garbage = garbage.substring(garbage.length());
								pretendedMemory.add(builder.toString());
							}
							int deleteCount = new Random().nextInt(15000);
							for (int i = -1; ++i != deleteCount; )
								pretendedMemory.removeFirst();

							System.out.println("-----------");
						}
					}
				}
			).start();
	}

	private Runtime context;
	private double maxFreeMemory;

	private long lastFreeMemory;
	private long lastTotalMemory;
	private long lastMaxMemory;

	private double lastMemoryRate;

	public PerformanceMonitor(Runtime context)
	{
		this.context = context;
	}

	public void checkAll()
	{
		this.monitorMemory();
		this.monitorCpu();
	}
	/**
	 * 本方法比较当前空余内存与历史记录最大空余内存的关系。若空余内存过小,则执行垃圾回收。
	 */
	public void monitorMemory()
	{
		// 求空余内存,并计算空余内存比起最大空余内存的比例
		long freeMemory = this.context.freeMemory();
		if (freeMemory > this.maxFreeMemory)
			this.maxFreeMemory = Long.valueOf(freeMemory).doubleValue();
		double memoryRate = freeMemory / this.maxFreeMemory;
		System.out.println("There are " + memoryRate * 100 + "% free memory.");

		// 如果内存空余率在变小,则一切正常;否则需要报告内存变化情况
		if (memoryRate >= this.lastMemoryRate) this.reportMemoryChange();

		// 如果内存空余率很低,则执行内存回收
		if (freeMemory / this.maxFreeMemory < 0.3)
		{
			System.out.print("System will start memory Garbage Collection.");
			System.out.println(" Now we have " + freeMemory / 1000 + " KB free memory.");
			this.context.gc();
			System.out.println("After the Garbage Collection, we have "
					+ this.context.freeMemory() / 1000 + " KB free memory.");
		}

		// 记录内存信息
		this.recordMemoryInfo(memoryRate);
	}

	/**
	 * 报告内存变化情况
	 */
	private void reportMemoryChange()
	{
		System.out.print("Last freeMemory = " + this.lastFreeMemory / 1000 + " KB,");
		System.out.println(" now it is " + this.context.freeMemory() / 1000 + " KB.");
		System.out.print("Last totalMemory = " + this.lastTotalMemory / 1000 + " KB,");
		System.out.println(" now it is " + this.context.totalMemory() / 1000 + " KB.");
		System.out.print("Last maxMemory = " + this.lastMaxMemory / 1000 + " KB,");
		System.out.println(" now it is " + this.context.maxMemory() / 1000 + " KB.");
	}

	/**
	 * 记录本次内存信息。
	 */
	private void recordMemoryInfo(double memoryRate)
	{
		this.lastFreeMemory = this.context.freeMemory();
		this.lastMaxMemory = this.context.maxMemory();
		this.lastTotalMemory = this.context.totalMemory();
		this.lastMemoryRate = memoryRate;
	}

	/**
	 * 监测 CPU 的方法。
	 */
	public void monitorCpu()
	{
		int cpuCount = this.context.availableProcessors();
		if (cpuCount > 1) System.out.println("CPU have " + cpuCount + " processors.");
	}
}
我运行这段程序,得到结果报告。通过观察结果报告,我得到了一些新结论。
首先, maxMemory 在一台机器只运行一个爪哇(Java)虚拟机的前提下,一般来说并不会变动。
其次,新生代内存会很快地自动回收,这体现在 freeMemory 总是不断少量自动增加上。
最后,爪哇(Java)虚拟机会在内存不足时,自己申请新的内存。这个内存空间也能够根据报告大概看出一点原则:既不是完全通过可用内存比例,也不是完全通过可用内存数量。

我自己运行的报告附在下边
There are 100.0% free memory.
Last freeMemory = 0 KB, now it is 124371 KB.
Last totalMemory = 0 KB, now it is 126353 KB.
Last maxMemory = 0 KB, now it is 1875378 KB.
CPU have 8 processors.
-----------
There are 79.91675736339026% free memory.
CPU have 8 processors.
-----------
There are 82.1353751773145% free memory.
Last freeMemory = 99921 KB, now it is 102695 KB.
Last totalMemory = 126353 KB, now it is 126353 KB.
Last maxMemory = 1875378 KB, now it is 1875378 KB.
CPU have 8 processors.
-----------
There are 100.0% free memory.
Last freeMemory = 102695 KB, now it is 140522 KB.
Last totalMemory = 126353 KB, now it is 159383 KB.
Last maxMemory = 1875378 KB, now it is 1875378 KB.
CPU have 8 processors.
-----------
There are 82.4930651724349% free memory.
CPU have 8 processors.
-----------
There are 65.90519105111919% free memory.
CPU have 8 processors.
-----------
There are 88.50612783993465% free memory.
Last freeMemory = 92611 KB, now it is 124371 KB.
Last totalMemory = 159383 KB, now it is 159383 KB.
Last maxMemory = 1875378 KB, now it is 1875378 KB.
CPU have 8 processors.
-----------
There are 71.68576727159902% free memory.
CPU have 8 processors.
-----------
There are 54.86540670326339% free memory.
CPU have 8 processors.
-----------
There are 100.0% free memory.
Last freeMemory = 77098 KB, now it is 172330 KB.
Last totalMemory = 159383 KB, now it is 225443 KB.
Last maxMemory = 1875378 KB, now it is 1875378 KB.
CPU have 8 processors.
-----------
There are 86.18976806966614% free memory.
CPU have 8 processors.
-----------
There are 72.37916940114857% free memory.
CPU have 8 processors.
-----------
There are 58.56890497502629% free memory.
CPU have 8 processors.
-----------
There are 46.292794574206056% free memory.
CPU have 8 processors.
-----------
There are 92.98754812452182% free memory.
Last freeMemory = 79776 KB, now it is 160245 KB.
Last totalMemory = 225443 KB, now it is 225443 KB.
Last maxMemory = 1875378 KB, now it is 1875378 KB.
CPU have 8 processors.
-----------
There are 79.17694945600425% free memory.
CPU have 8 processors.
-----------
There are 65.36668502988196% free memory.
CPU have 8 processors.
-----------
There are 51.556035296554015% free memory.
CPU have 8 processors.
-----------
There are 37.745845146519564% free memory.
CPU have 8 processors.
-----------
There are 23.935246478001996% free memory.
System will start memory Garbage Collection. Now we have 41247 KB free memory.
After the Garbage Collection, we have 312897 KB free memory.
CPU have 8 processors.
-----------
There are 100.0% free memory.
Last freeMemory = 312897 KB, now it is 292267 KB.
Last totalMemory = 380108 KB, now it is 380108 KB.
Last maxMemory = 1875378 KB, now it is 1875378 KB.
CPU have 8 processors.
-----------
There are 91.1770148111291% free memory.
CPU have 8 processors.
-----------
There are 84.11856206174096% free memory.
CPU have 8 processors.
-----------
There are 75.29548107031924% free memory.
CPU have 8 processors.
-----------
There are 68.2370940141088% free memory.
CPU have 8 processors.
-----------
There are 59.414100613590705% free memory.
CPU have 8 processors.
-----------
There are 52.35564786420257% free memory.
CPU have 8 processors.
-----------
There are 43.53256687278083% free memory.
CPU have 8 processors.
-----------
There are 34.70958168390994% free memory.
CPU have 8 processors.
-----------
There are 27.6511289345218% free memory.
System will start memory Garbage Collection. Now we have 80815 KB free memory.
After the Garbage Collection, we have 281843 KB free memory.
CPU have 8 processors.
-----------
There are 89.37604181852511% free memory.
Last freeMemory = 281843 KB, now it is 261217 KB.
Last totalMemory = 380108 KB, now it is 380108 KB.
Last maxMemory = 1875378 KB, now it is 1875378 KB.
CPU have 8 processors.
-----------
There are 80.55442250030752% free memory.
CPU have 8 processors.
-----------
There are 73.49712485596086% free memory.
CPU have 8 processors.
-----------
There are 64.67547542837015% free memory.
CPU have 8 processors.
-----------
There are 57.618177784023494% free memory.
CPU have 8 processors.
-----------
There are 48.79652835643279% free memory.
CPU have 8 processors.
-----------
There are 41.739230712086126% free memory.
CPU have 8 processors.
-----------
There are 32.91758128449542% free memory.
CPU have 8 processors.
-----------
There are 24.095931856904713% free memory.
System will start memory Garbage Collection. Now we have 70424 KB free memory.
After the Garbage Collection, we have 258135 KB free memory.
CPU have 8 processors.
-----------
There are 81.32306278893708% free memory.
Last freeMemory = 258135 KB, now it is 237681 KB.
Last totalMemory = 380108 KB, now it is 380108 KB.
Last maxMemory = 1875378 KB, now it is 1875378 KB.
CPU have 8 processors.
-----------
There are 72.5752415442342% free memory.
CPU have 8 processors.
-----------
There are 65.57687068029719% free memory.
CPU have 8 processors.
-----------
There are 56.828918049238894% free memory.
CPU have 8 processors.
-----------
There are 49.83056634581206% free memory.
CPU have 8 processors.
-----------
There are 41.08271772895181% free memory.
CPU have 8 processors.
-----------
There are 32.33487732373877% free memory.
CPU have 8 processors.
-----------
There are 25.33650645980177% free memory.
System will start memory Garbage Collection. Now we have 74050 KB free memory.
After the Garbage Collection, we have 229217 KB free memory.
CPU have 8 processors.
-----------
There are 71.73676393326296% free memory.
Last freeMemory = 229217 KB, now it is 209663 KB.
Last totalMemory = 380108 KB, now it is 380108 KB.
Last maxMemory = 1875378 KB, now it is 1875378 KB.
CPU have 8 processors.
-----------
There are 63.37379248412019% free memory.
CPU have 8 processors.
-----------
There are 55.01088399093938% free memory.
CPU have 8 processors.
-----------
There are 46.64788243242348% free memory.
CPU have 8 processors.
-----------
There are 38.28488087390758% free memory.
CPU have 8 processors.
-----------
There are 31.59450152482077% free memory.
CPU have 8 processors.
-----------
There are 23.231593031639967% free memory.
System will start memory Garbage Collection. Now we have 67898 KB free memory.
After the Garbage Collection, we have 203384 KB free memory.
CPU have 8 processors.
-----------
There are 61.86563040788292% free memory.
Last freeMemory = 203384 KB, now it is 180813 KB.
Last totalMemory = 380108 KB, now it is 380108 KB.
Last maxMemory = 1875378 KB, now it is 1875378 KB.
CPU have 8 processors.
-----------

我最近(2012-11-6 Tuesday 至 2012-11-20 Tuesday)参加了一个博客大赛。欢迎来给我投一票~
投票地址: http://blog.51cto.com/contest2012/5523233 每个 IP 每天可以投一票哦~

本文也发表在我的其他空间。
ITeye : http://surmounting.iteye.com/blog/1724328
开源中国: http://my.oschina.net/shane1984/blog/88803
51CTO : http://shanelooli.blog.51cto.com/5523233/1058490


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