JAVA運行時問題診斷-工具應用篇

2019-11-14 15:40:29

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該BLOG內容是之前在部門組織討論運行時問題時自己寫的PPT內容，內容以點帶面，主要是方便以后自己回顧查看。

大綱包括：1、運行時問題分類 2、服務器自帶工具 3、其他工具 4、例子 5、實際情況

運行時問題分類-軟件角度：1、內存泄漏，對象未釋放 2、線程阻塞、死鎖 3、線程死循環 4、網絡IO連接超時時間過長 5、磁盤不可寫 .....

運行時問題分類-硬件角度：1、內存占用高 2、CPU占用高 3、網絡無反應 4、硬盤空間滿 ....

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：

實時分析工具： 1、Jconsole 2、VisualVM 3、JPRofiler 4、javaMelody 5、LambdaProbe ....

離線分析工具： 1、MemoryAnalyzer tool 2、Thread Dump Analyzer ....

DEMO：1、內存溢出 2、CPU占用過高 3、線程死鎖 4、線程阻塞

準備工作：堆棧內存設置低一點，打印GC日志和OOM時輸出dump文件： set JAVA_OPTS=-server -Xms24m -Xmx50m -XX:PermSize=28M -XX:MaxPermSize=80m -XX:+PrintGCDetails -XX:+HeapDumpOnOutOfMemoryError -XX:HeapDumpPath=d:/temp/dump

內存溢出：

        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-關鍵字(個人理解，不一定準確):

Histogram：內存中的類對象實例的對象的個數和大小

Dominator Tree：堆對象樹，對象大小和占用百分比

Leak Suspects：MAT分析的內存泄漏的可疑點

shallow heap：對象自身占用內存大小

retained heap：對象自身和引用的對象占用內存大小

Merge Shortest Paths to GC Roots：從GC根節點到該對象的路徑視圖

with outgoing references：對象持有的外部對象引用

with incomming references：對象被哪些外部對象引用

....

CPU占用過高：

		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();			}		}

線程死鎖:

		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("主線程 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();		}	}

線程阻塞：

		WaitThread thread1 = new WaitThread();		thread1.setName("線程1");		NotifyThread thread2 = new NotifyThread();		thread2.setName("線程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("線程" + Thread.currentThread().getName() + "占用了鎖");			try {				Thread.sleep(20000);			} catch (InterruptedException e) {				// TODO Auto-generated catch block				e.printStackTrace();			}			RequestThreadWait.object.notify();			System.out.println("線程" + Thread.currentThread().getName() + "調用了object.notify()");			try {				Thread.sleep(20000);			} catch (InterruptedException e) {				// TODO Auto-generated catch block				e.printStackTrace();			}		}		System.out.println("線程" + Thread.currentThread().getName() + "釋放了鎖");	}}public class WaitThread extends Thread {	public void run() {		synchronized (RequestThreadWait.object) {			System.out.println("線程" + Thread.currentThread().getName() + "獲取到了鎖開始");			try {				RequestThreadWait.object.wait();			} catch (InterruptedException e) {			}			System.out.println("線程" + Thread.currentThread().getName() + "獲取到了鎖結束！");		}	}}