死锁编码与分析

死锁产生的主要原因：两个或两个以上进程在执行过程中，因争夺资源而造成的一种循环等待现象，若无外力干涉它们将无法推进下去

• 编码

class HoldLockThread implements Runnable{
    private String lockA;
    private String lockB;
    public HoldLockThread(String lockA, String lockB) {
        this.lockA = lockA;
        this.lockB = lockB;
    }
    @Override
    public void run() {
        synchronized (lockA){
            System.out.println(Thread.currentThread().getName()+"\t 自己持有:"+lockA+"  尝试获得:"+lockB);
            try {TimeUnit.SECONDS.sleep(2);} catch (InterruptedException e){e.printStackTrace();}
            synchronized (lockB){
                System.out.println(Thread.currentThread().getName()+"\t 自己持有:"+lockB+"  尝试获得:"+lockA);
            }
        }
    }
}
public class DeadLockDemo {
    public static void main(String[] args) {
        String str1="str1";
        String str2="str2";  //两个资源

        new Thread(new HoldLockThread(str1,str2),"AAA").start();
        new Thread(new HoldLockThread(str2,str1),"BBB").start();
    }
}

运行结果：

两个线程操纵两个资源 str1与str2，AAA线程获取str1的锁之后，进入休眠，此时BBB线程进来获取了str2的锁，尝试获取str1的锁，但是str1的锁被AAA线程占有，AAA线程苏醒，尝试获取str2的锁，str2被线程BBB占有，所以就出现了循环等待现象，就是死锁

• 定位分析

 jps  -l    命令查看运行程序进程号

D:\IntelliJIDEAproject\InterviewFirst>jps -l
2880 org.jetbrains.jps.cmdline.Launcher
3952 org.jetbrains.jps.cmdline.Launcher
13448 org.jetbrains.kotlin.daemon.KotlinCompileDaemon
15276 sun.tools.jps.Jps
15996 eight.DeadLockDemo
5996

jstack 进程号   命令定位分析 确认是死锁！

=============================
"BBB":
  waiting to lock monitor 0x00000000033ab1a8 (object 0x00000000d5f7cda8, a java.lang.String),
  which is held by "AAA"
"AAA":
  waiting to lock monitor 0x00000000033a8868 (object 0x00000000d5f7cdd8, a java.lang.String),
  which is held by "BBB"

Java stack information for the threads listed above:
===================================================
"BBB":
        at eight.HoldLockThread.run(DeadLockDemo.java:21)
        - waiting to lock <0x00000000d5f7cda8> (a java.lang.String)
        - locked <0x00000000d5f7cdd8> (a java.lang.String)
        at java.lang.Thread.run(Thread.java:748)
"AAA":
        at eight.HoldLockThread.run(DeadLockDemo.java:21)
        - waiting to lock <0x00000000d5f7cdd8> (a java.lang.String)
        - locked <0x00000000d5f7cda8> (a java.lang.String)
        at java.lang.Thread.run(Thread.java:748)

Found 1 deadlock.