多线程死锁分析

编写下面代码，用于演示死锁情况：

public class ThreadDeadlock {

      public static void main(String[] args) throws InterruptedException {

            Object obj1 = new Object();

            Object obj2 = new Object();

            Object obj3 = new Object();

            

            Thread t1 = new Thread( new SyncThread(obj1, obj2), "t1");

        Thread t2 = new Thread( new SyncThread(obj2, obj3), "t2");

        Thread t3 = new Thread( new SyncThread(obj3, obj1), "t3");

 

        t1.start();

        Thread.sleep(5000);

        t2.start();

        Thread.sleep(5000);

        t3.start();

      }

}

class SyncThread implements Runnable {

      private Object obj1;

      private Object obj2;

      public SyncThread(Object obj1, Object obj2) {

             this. obj1 = obj1;

             this. obj2 = obj2;

      }

      @Override

      public void run() {

            String name = Thread. currentThread().getName();

            System. out.println(name + "申请锁:"+obj1 );

             synchronized ( obj1) {

                  System. out.println(name + "获取锁:"+obj1 );

                  work();

                  System. out.println(name + "申请锁:"+obj2 );

                   synchronized ( obj2) {

                        System. out.println(name + "获取锁:"+obj2 );

                        work();

                  }

                  System. out.println(name + "释放锁:"+obj2 );

            }

            System. out.println(name + "释放锁:"+obj1 );

            System. out.println(name + "运行结束");

      }

      

      private void work(){

             try {

                  Thread. sleep(30000);

            } catch (InterruptedException e) {

                  e.printStackTrace();

            }

      }

}

执行上面的程序时，就产生了输出，但是程序却因为死锁无法停止

t1申请锁:java.lang.Object@1d87b360
t1获取锁:java.lang.Object@1d87b360
t2申请锁:java.lang.Object@47bb2cb
t2获取锁:java.lang.Object@47bb2cb
t3申请锁:java.lang.Object@653e4653
t3获取锁:java.lang.Object@653e4653
t1申请锁:java.lang.Object@47bb2cb
t2申请锁:java.lang.Object@653e4653
t3申请锁:java.lang.Object@1d87b360

要分析线程执行情况，需要用工具 dump 线程信息。可以使用 VisualVM (http://visualvm.java.net/)

运行 VisualVM，直接右键就可以Dump

如果在linux 上 可以用jdk 提供 jstack 工具：

ps -eaf|grep java    找到PID

jstack 26444 >> ~/a.dump

参考文章：
http://www.importnew.com/9668.html
http://www.journaldev.com/1053/how-to-generate-thread-dump-in-java