实战

准备项目

随便找个SpringBoot项目

package com.example.demo;
/**
 */
public class DeadLockTest extends Thread {
    private String first;
    private String second;
    public DeadLockTest(String name, String first, String second) {
        super(name);
        this.first = first;
        this.second = second;
    }
    public  void run() {
        synchronized (first) {
            try {
                System.out.println(this.getName() + " ...synchronized:===>  first " + first);
                Thread.sleep(1000L);
                synchronized (second) {
                    System.out.println(this.getName() + " ...synchronized:===>  second  " + second);
                }
            } catch (InterruptedException e) {}
        }
    }
    public static void main(String[] args) throws InterruptedException {
        String lockA = "lockA";
        String lockB = "lockB";
        DeadLockTest t1 = new DeadLockTest("t1", lockA, lockB);
        DeadLockTest t2 = new DeadLockTest("t2", lockB, lockA);
        t1.start();
        t2.start();
        t1.join();
        t2.join();
    }
}

package com.example.demo;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;
@SpringBootApplication
@RestController
public class DemoApplication {
    public static void main(String[] args) {
        SpringApplication.run(DemoApplication.class, args);
    }
      @GetMapping("/hello")
        public String c_ () throws InterruptedException {
          String lockA = "lockA";
          String lockB = "lockB";
          DeadLockTest t1 = new DeadLockTest("t1", lockA, lockB);
          DeadLockTest t2 = new DeadLockTest("t2", lockB, lockA);
          t1.start();
          t2.start();
          t1.join();
          t2.join();
        return "你好";
        }
}

打包部署

这个我就不演示了,将你自己的项目打包, 部署到 linux上,这个我就不演示了,,大家都会.

访问网址

浏览器get请求敲击url: http://zjj101:8080/demo/hello ,发现浏览器一直在转圈圈,说明一直访问不通.

看tomcat日志发现已经是死锁状态了.

t1 ...synchronized:===>  first lockA
t2 ...synchronized:===>  first lockB

使用jstack工具

查看进程号

使用 ps -ef|grep java 命令查看到Java进程是11271

[root@zjj101 logs]# ps -ef|grep java
root      11271      1  3 09:45 pts/0    00:00:24 /usr/bin/java -Djava.util.logging.config.file=/root/apache-tomcat-8.5.28/conf/logging.properties -Djava.util.logging.manager=org.apache.juli.ClassLoaderLogManager -Djdk.tls.ephemeralDHKeySize=2048 -Djava.protocol.handler.pkgs=org.apache.catalina.webresources -Dignore.endorsed.dirs= -classpath /root/apache-tomcat-8.5.28/bin/bootstrap.jar:/root/apache-tomcat-8.5.28/bin/tomcat-juli.jar -Dcatalina.base=/root/apache-tomcat-8.5.28 -Dcatalina.home=/root/apache-tomcat-8.5.28 -Djava.io.tmpdir=/root/apache-tomcat-8.5.28/temp org.apache.catalina.startup.Bootstrap start

将日志导出到文件中

使用 jstack -l [进程号]>deadlock.jstack 命令将日志导出到deadlock.jstack文件中

[root@zjj101 logs]# jstack -l 11271 >deadlock.jstack
[root@zjj101 logs]# ls
catalina.2021-10-12.log      localhost.2021-10-12.log
catalina.out                 localhost_access_log.2021-10-12.txt
deadlock.jstack              manager.2021-10-12.log
host-manager.2021-10-12.log

查看日志文件

使用less命令查看,

敲击命令: less deadlock.jstack

然后打开文件一直翻,直到找到 “Found one Java-level deadlock:”字眼的东西,

然后看”Java stack information for the threads listed above:”下的内容, 上面说了两个线程在 DeadLockTest.java:21 行锁住了.

Found one Java-level deadlock:
=============================
"t2":
  waiting to lock monitor 0x00007f61983ba9e8 (object 0x00000000e90f32c8, a java.lang.String),
  which is held by "t1"
"t1":
  waiting to lock monitor 0x00007f61983bfe78 (object 0x00000000e90f3300, a java.lang.String),
  which is held by "t2"

Java stack information for the threads listed above:
===================================================
"t2":
        at com.example.demo.DeadLockTest.run(DeadLockTest.java:21)
        - waiting to lock <0x00000000e90f32c8> (a java.lang.String)
        - locked <0x00000000e90f3300> (a java.lang.String)
"t1":
        at com.example.demo.DeadLockTest.run(DeadLockTest.java:21)
        - waiting to lock <0x00000000e90f3300> (a java.lang.String)
        - locked <0x00000000e90f32c8> (a java.lang.String)

Found 1 deadlock.

查看你自己写的代码

发现的确是这里锁住了,然后你就去修改代码即可