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[Java教程]JAVA运行时问题诊断

该BLOG内容是之前在部门组织讨论运行时问题时自己写的PPT内容,内容以点带面,主要是方便以后自己回顾查看。

大纲包括:1、运行时问题分类 2、服务器自带工具 3、其他工具 4、例子 5、实际情况

运行时问题分类-软件角度:1、内存泄漏,对象未释放 2、线程阻塞、死锁 3、线程死循环 4、网络IO连接超时时间过长 5、磁盘不可写 .....

运行时问题分类-硬件角度:1、内存占用高 2、CPU占用高 3、网络无反应 4、硬盘空间满 ....

Linux指令:1、top, top -Hp pid 2、free 3、df 4、netstat, netstat -natp ...

JDK指令:1、jps, jps -v 2、jstack, jstack pid 3、jmap, jmap -dump:format=b,file=/opt/...  4、jstat, jstat -gcutil(gc,gccapacity) pid ....

工具:

实时分析工具: 1、Jconsole 2、VisualVM  3、JProfiler  4、JavaMelody  5、LambdaProbe ....

离线分析工具: 1、MemoryAnalyzer tool  2、Thread Dump Analyzer ....

DEMO:1、内存溢出  2、CPU占用过高  3、线程死锁  4、线程阻塞

准备工作:堆栈内存设置低一点,打印GC日志和OOM时输出dump文件: set JAVA_OPTS=-server -Xms24m -Xmx50m -XX:PermSize=28M -XX:MaxPermSize=80m -XX:+PrintGCDetails -XX:+HeapDumpOnOutOfMemoryError -XX:HeapDumpPath=d:\temp\dump

内存溢出:

    Map<String, Person> map = new HashMap<String, Person>();    Object[] array = new Object[1000000];    for (int i = 0; i < 1000000; i++) {      String d = new Date().toString();      Person p = new Person(d, i);      map.put(i + "person", p);      array[i] = p;    }

MAT-关键字(个人理解,不一定准确):

Histogram:内存中的类对象实例的对象的个数和大小

Dominator Tree:堆对象树,对象大小和占用百分比

Leak Suspects:MAT分析的内存泄漏的可疑点

shallow heap:对象自身占用内存大小

retained heap:对象自身和引用的对象占用内存大小

Merge Shortest Paths to GC Roots:从GC根节点到该对象的路径视图

with outgoing references:对象持有的外部对象引用

with incomming references:对象被哪些外部对象引用

....

 

CPU占用过高:

		int i = 0;		while (i < 1000000) {			i++;			System.out.println(i);			try {				Thread.sleep(0);			} catch (InterruptedException e) {				// TODO Auto-generated catch block				e.printStackTrace();			}		}

  

 

线程死锁:

		Thread t1 = new Thread(new SyncThread(obj1, obj2), "t1");		Thread t2 = new Thread(new SyncThread(obj2, obj1), "t2");		t1.start();		try {			Thread.sleep(3000);		} catch (InterruptedException e) {			// TODO Auto-generated catch block			e.printStackTrace();		}		t2.start();		synchronized (obj1) {			System.out.println("主线程 lock on " + obj1.getName());		}

  

	private Person obj1;	private Person obj2;	public SyncThread(Person o1, Person o2) {		this.obj1 = o1;		this.obj2 = o2;	}	public void run() {		String name = Thread.currentThread().getName();		System.out.println(name + " acquiring lock on " + obj1.getName());		synchronized (obj1) {			System.out.println(name + " acquired lock on " + obj1.getName());			work();			System.out.println(name + " acquiring lock on " + obj2.getName());			synchronized (obj2) {				System.out.println(name + " acquired lock on " + obj2.getName());				work();			}			System.out.println(name + " released lock on " + obj2.getName());		}		System.out.println(name + " released lock on " + obj1.getName());		System.out.println(name + " finished execution.");	}	private void work() {		try {			Thread.sleep(10000);		} catch (InterruptedException e) {			e.printStackTrace();		}	}

  

 

线程阻塞:

		WaitThread thread1 = new WaitThread();		thread1.setName("线程1");		NotifyThread thread2 = new NotifyThread();		thread2.setName("线程2");		thread1.start();		try {			Thread.sleep(20000);		} catch (InterruptedException e) {			e.printStackTrace();		}		thread2.start();

  

public class NotifyThread extends Thread {	@Override	public void run() {		synchronized (RequestThreadWait.object) {			System.out.println("线程" + Thread.currentThread().getName() + "占用了锁");			try {				Thread.sleep(20000);			} catch (InterruptedException e) {				// TODO Auto-generated catch block				e.printStackTrace();			}			RequestThreadWait.object.notify();			System.out.println("线程" + Thread.currentThread().getName() + "调用了object.notify()");			try {				Thread.sleep(20000);			} catch (InterruptedException e) {				// TODO Auto-generated catch block				e.printStackTrace();			}		}		System.out.println("线程" + Thread.currentThread().getName() + "释放了锁");	}}public class WaitThread extends Thread {	public void run() {		synchronized (RequestThreadWait.object) {			System.out.println("线程" + Thread.currentThread().getName() + "获取到了锁开始");			try {				RequestThreadWait.object.wait();			} catch (InterruptedException e) {			}			System.out.println("线程" + Thread.currentThread().getName() + "获取到了锁结束!");		}	}}

  

线程状态(个人理解,不一定准确):

WAITING (parking):线程自身挂起等待,正常

WAITING (on object monitor):线程主动执行wait,等待资源,如果是自己的程序,需要关注

BLOCKED (on object monitor):线程阻塞,等待对方释放资源,如果是互相等待对方阻塞的线程,则发生死锁

TIMED_WAITING (on object monitor):线程调用了wait(long timeout),在特定时间内等待

TIMED_WAITING (sleeping):调用了sleeping,休眠一段时间

 

JavaMelody:

LambdaProbe

 

实际情况:

用户反馈各种千奇百怪的问题!

网络访问连接不上

网站、接口访问超时

特定功能很慢

部分功能部分人打不开

.......

->

ping,telnet,traceroute....

top,top -Hp pid,jstack pid....

jstat -gc,gcutil,gccapacity pid...

jmap -dump:format=b,file=/opt/.... tail, df -lh....

netstat -natp....

.....

生产问题没有统一解决办法,具体问题具体分析

内存查看:jstat

线程情况查看:top -Hp pid

CPU查看:jstack

网络查看:netstat

 

实际问题分析:

线上查看 服务器情况分析 获取内存dump 获取javacore

线下分析 工具调试分析内存线程

代码调试 Eclipse Class Decompiler(自动反编译,选择JD-Core,精确行数)

...

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上面是实际生产问题的自己写的PPT,copy下来的,JDK自带的工具和指令比较强大,本篇文章没有太多介绍。