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！");		}	}}