一、模擬死鎖

public class App 
{
    public static void main( String[] args )
    {
        Object object1 = new Object();
        Object object2 = new Object();

        System.out.println("main thread start");
        Thread thread1 = new Thread(new Task1(object1,object2));
        thread1.start();


        Thread thread2 = new Thread(new Task2(object1,object2));
        thread2.start();

        System.out.println("main thread end");

    }

}

class Task1 implements Runnable {

    private Object curObj1;
    private Object curObj2;

    public Task1 (Object obj1,Object obj2) {
        this.curObj1 = obj1;
        this.curObj2 = obj2;
    }

    public void run() {
        System.out.println(Thread.currentThread().getName() + " start");

        synchronized (curObj1) {
            System.out.println(Thread.currentThread().getName() + " get lock on Object1");

            try {
                TimeUnit.SECONDS.sleep(2);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }

            synchronized (curObj2) {
                System.out.println(Thread.currentThread().getName() + " get lock on Object2");
            }

        }

        System.out.println(Thread.currentThread().getName() + " end");
    }
}

class Task2 implements Runnable {

    private Object curObj1;
    private Object curObj2;

    public Task2 (Object obj1,Object obj2) {
        this.curObj1 = obj1;
        this.curObj2 = obj2;
    }

    public void run() {
        System.out.println(Thread.currentThread().getName() + " start");

        synchronized (curObj2) {
            System.out.println(Thread.currentThread().getName() + " get lock on Object2");

            try {
                TimeUnit.SECONDS.sleep(2);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }

            synchronized (curObj1) {
                System.out.println(Thread.currentThread().getName() + " get lock on Object1");
            }
        }



        System.out.println(Thread.currentThread().getName() + " end");
    }
}
 

1、兩個執行緒分別互相等待對方釋放物件鎖

2、打包成jar（注意在POM中加入maven-jar-plugin外掛，否則打包出來的jar在執行時會報錯找不到manifest）

3、java  -jar   jarname  執行

二、排查死鎖

1、top檢視CPU和記憶體使用率

2、找到資源佔用率比較高的程序PID

3、分析PID

4、顯示PID下面的執行緒

     top -H  -p  pid

5、檢視具體某個執行緒

     jstack -l  pid | grep  xxx -A  20

6、jvm常用命令

（1）jps 檢視啟動的JVM程序

（2）jinfo  pid 檢視某個JVM程序ClassPath、VM引數設定等

（3）jstat 檢視某個JVM程序執行狀態：GC情況等

（4）jstack 檢視某個JVM程序下所有執行緒的執行狀態

（5）jmap 檢視某個JVM程序下堆中儲存的物件

檢視結果：