Thread Dead Lock Demo

产生死锁原因：在多线程或者多进程中，两个或者两个以上线程或者进程占有共有资源，并且互相等待对方持有资源，出现相互等待的状态或者产生僵死的状态。成为死锁

死锁四个必要条件：
1、互斥条件

2、请求与等待条件

3、不可剥夺条件

4、循环等待条件

package com.chen.test.Thread.DeadLockDemo;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

public class DeadLockDemo {
    private static final Logger log = LoggerFactory.getLogger(DeadLockDemo.class);

    //new two resource object
    private static Object resource1 = new Object();
    private static Object resource2 = new Object();

    //ThreadA
    public static class ThreadA extends Thread{
        @Override
        public void run() {
            synchronized (resource1){
             log.info(Thread.currentThread() +"ThreadA get resource1 !");
             try{
                 log.info(Thread.currentThread() + "ThreadA sleep 2s ,for ThreadB get resource2!");
                 sleep(2000);

             }catch (InterruptedException e){
                 e.printStackTrace();
             }
             log.info(Thread.currentThread() + "ThreadA waiting resource2!");
             synchronized (resource2){
                 log.info(Thread.currentThread() + "ThreadA get resource2!");
             }
            }
        }
    }

    //ThreadB
    public static class ThreadB extends Thread{
        @Override
        public void run(){
            synchronized (resource2){
                log.info(Thread.currentThread() + "ThreadB get resource2!");
                try{
                    log.info(Thread.currentThread()+ "ThreadB sleep 2s , for ThreadA get resource1 !");
                    sleep(2000);
                }catch (InterruptedException e){
                    e.printStackTrace();
                }

                log.info(Thread.currentThread() + "ThreadB waiting resource1!");
                synchronized (resource1){
                    log.info(Thread.currentThread() + "ThreadB get resource1!");
                }
            }
        }
    }

    //main Method
    public static void main(String[] args) {
        ThreadA threadA = new ThreadA();
        ThreadB threadB = new ThreadB();
        threadA.start();
        threadB.start();
    }
}

结果：

 查看死锁的方法：jstack 进程号 ，jdk工具中自带查看java堆栈信息工具

1、先用jps  -l  或者jcmd -l 查询进程号

2、再用jstack -l 进程号 查询堆栈信息

jps -l 或者 jcmd -l

jstack -l 62744

查询结果：可以看到死锁信息：BLOCKED是死锁线程

2022-04-26 11:33:20
Full thread dump Java HotSpot(TM) 64-Bit Server VM (25.221-b11 mixed mode):

"DestroyJavaVM" #14 prio=5 os_prio=0 tid=0x0000000002b26000 nid=0xec34 waiting on condition [0x0000000000000000]
   java.lang.Thread.State: RUNNABLE

   Locked ownable synchronizers:
        - None

"Thread-1" #13 prio=5 os_prio=0 tid=0x000000001f074800 nid=0xce3c waiting for monitor entry [0x000000001f9ef000]
   java.lang.Thread.State: BLOCKED (on object monitor)
        at com.chen.test.Thread.DeadLockDemo.DeadLockDemo$ThreadB.run(DeadLockDemo.java:49)
        - waiting to lock <0x000000076e5f5ad8> (a java.lang.Object)
        - locked <0x000000076e5f5ae8> (a java.lang.Object)

   Locked ownable synchronizers:
        - None

"Thread-0" #12 prio=5 os_prio=0 tid=0x000000001f071000 nid=0xc360 waiting for monitor entry [0x000000001f8ef000]
   java.lang.Thread.State: BLOCKED (on object monitor)
        at com.chen.test.Thread.DeadLockDemo.DeadLockDemo$ThreadA.run(DeadLockDemo.java:28)
        - waiting to lock <0x000000076e5f5ae8> (a java.lang.Object)
        - locked <0x000000076e5f5ad8> (a java.lang.Object)

   Locked ownable synchronizers:
        - None

"Service Thread" #11 daemon prio=9 os_prio=0 tid=0x000000001ed8a800 nid=0xf300 runnable [0x0000000000000000]
   java.lang.Thread.State: RUNNABLE

   Locked ownable synchronizers:
        - None

"C1 CompilerThread3" #10 daemon prio=9 os_prio=2 tid=0x000000001e3de000 nid=0xd56c waiting on condition [0x0000000000000000]
   java.lang.Thread.State: RUNNABLE

   Locked ownable synchronizers:
        - None

"C2 CompilerThread2" #9 daemon prio=9 os_prio=2 tid=0x000000001e3ad800 nid=0xdcc8 waiting on condition [0x0000000000000000]
   java.lang.Thread.State: RUNNABLE

   Locked ownable synchronizers:
        - None

"C2 CompilerThread1" #8 daemon prio=9 os_prio=2 tid=0x000000001e3ab000 nid=0xfeb4 waiting on condition [0x0000000000000000]
   java.lang.Thread.State: RUNNABLE

   Locked ownable synchronizers:
        - None

"C2 CompilerThread0" #7 daemon prio=9 os_prio=2 tid=0x000000001e3a8000 nid=0xdfa8 waiting on condition [0x0000000000000000]
   java.lang.Thread.State: RUNNABLE

   Locked ownable synchronizers:
        - None

"Monitor Ctrl-Break" #6 daemon prio=5 os_prio=0 tid=0x000000001e3db800 nid=0xf750 runnable [0x000000001e93f000]
   java.lang.Thread.State: RUNNABLE
        at java.net.SocketInputStream.socketRead0(Native Method)
        at java.net.SocketInputStream.socketRead(SocketInputStream.java:116)
        at java.net.SocketInputStream.read(SocketInputStream.java:171)
        at java.net.SocketInputStream.read(SocketInputStream.java:141)
        at sun.nio.cs.StreamDecoder.readBytes(StreamDecoder.java:284)
        at sun.nio.cs.StreamDecoder.implRead(StreamDecoder.java:326)
        at sun.nio.cs.StreamDecoder.read(StreamDecoder.java:178)
        - locked <0x000000076dfc05e0> (a java.io.InputStreamReader)
        at java.io.InputStreamReader.read(InputStreamReader.java:184)
        at java.io.BufferedReader.fill(BufferedReader.java:161)
        at java.io.BufferedReader.readLine(BufferedReader.java:324)
        - locked <0x000000076dfc05e0> (a java.io.InputStreamReader)
        at java.io.BufferedReader.readLine(BufferedReader.java:389)
        at com.intellij.rt.execution.application.AppMainV2$1.run(AppMainV2.java:48)

   Locked ownable synchronizers:
        - None

"Attach Listener" #5 daemon prio=5 os_prio=2 tid=0x000000001e07e800 nid=0x2b70 waiting on condition [0x0000000000000000]
   java.lang.Thread.State: RUNNABLE

   Locked ownable synchronizers:
        - None

"Signal Dispatcher" #4 daemon prio=9 os_prio=2 tid=0x000000001e0d8800 nid=0x90c4 runnable [0x0000000000000000]
   java.lang.Thread.State: RUNNABLE

   Locked ownable synchronizers:
        - None

"Finalizer" #3 daemon prio=8 os_prio=1 tid=0x0000000002c1c000 nid=0xd4ac in Object.wait() [0x000000001e63e000]
   java.lang.Thread.State: WAITING (on object monitor)
        at java.lang.Object.wait(Native Method)
        - waiting on <0x000000076dd08ed8> (a java.lang.ref.ReferenceQueue$Lock)
        at java.lang.ref.ReferenceQueue.remove(ReferenceQueue.java:144)
        - locked <0x000000076dd08ed8> (a java.lang.ref.ReferenceQueue$Lock)
        at java.lang.ref.ReferenceQueue.remove(ReferenceQueue.java:165)
        at java.lang.ref.Finalizer$FinalizerThread.run(Finalizer.java:216)

   Locked ownable synchronizers:
        - None

"Reference Handler" #2 daemon prio=10 os_prio=2 tid=0x000000001e061800 nid=0x2584 in Object.wait() [0x000000001e53f000]
   java.lang.Thread.State: WAITING (on object monitor)
        at java.lang.Object.wait(Native Method)
        - waiting on <0x000000076dd06c00> (a java.lang.ref.Reference$Lock)
        at java.lang.Object.wait(Object.java:502)
        at java.lang.ref.Reference.tryHandlePending(Reference.java:191)
        - locked <0x000000076dd06c00> (a java.lang.ref.Reference$Lock)
        at java.lang.ref.Reference$ReferenceHandler.run(Reference.java:153)

   Locked ownable synchronizers:
        - None

"VM Thread" os_prio=2 tid=0x000000001c259800 nid=0xe9d0 runnable

"GC task thread#0 (ParallelGC)" os_prio=0 tid=0x0000000002b3b800 nid=0xe2bc runnable

"GC task thread#1 (ParallelGC)" os_prio=0 tid=0x0000000002b3d000 nid=0xe914 runnable

"GC task thread#2 (ParallelGC)" os_prio=0 tid=0x0000000002b3e800 nid=0xefd0 runnable

"GC task thread#3 (ParallelGC)" os_prio=0 tid=0x0000000002b41000 nid=0xf464 runnable

"GC task thread#4 (ParallelGC)" os_prio=0 tid=0x0000000002b43800 nid=0xf424 runnable

"GC task thread#5 (ParallelGC)" os_prio=0 tid=0x0000000002b44800 nid=0xd5c0 runnable

"GC task thread#6 (ParallelGC)" os_prio=0 tid=0x0000000002b48000 nid=0xf8c4 runnable

"GC task thread#7 (ParallelGC)" os_prio=0 tid=0x0000000002b49000 nid=0xbf50 runnable

"VM Periodic Task Thread" os_prio=2 tid=0x000000001ee37800 nid=0xe5c4 waiting on condition

JNI global references: 12


Found one Java-level deadlock:
=============================
"Thread-1":
  waiting to lock monitor 0x000000001c2635b8 (object 0x000000076e5f5ad8, a java.lang.Object),
  which is held by "Thread-0"
"Thread-0":
  waiting to lock monitor 0x000000001c2612a8 (object 0x000000076e5f5ae8, a java.lang.Object),
  which is held by "Thread-1"

Java stack information for the threads listed above:
===================================================
"Thread-1":
        at com.chen.test.Thread.DeadLockDemo.DeadLockDemo$ThreadB.run(DeadLockDemo.java:49)
        - waiting to lock <0x000000076e5f5ad8> (a java.lang.Object)
        - locked <0x000000076e5f5ae8> (a java.lang.Object)
"Thread-0":
        at com.chen.test.Thread.DeadLockDemo.DeadLockDemo$ThreadA.run(DeadLockDemo.java:28)
        - waiting to lock <0x000000076e5f5ae8> (a java.lang.Object)
        - locked <0x000000076e5f5ad8> (a java.lang.Object)

Found 1 deadlock.

 处理死锁方法，破坏死锁四个必要条件，由于资源互斥条件是资源固有的特性是没办法改变的

1、破坏 “不可剥夺条件”

2、破坏 “请求与等待条件”

3、破坏 “循环等待条件”

产生死锁的原因是互斥条件、请求与等待条件、不可剥夺条件、循环等待条件，那么只要破坏死锁这四个必要条件，就可以避免死锁的产生。所以避免死锁的方法破坏四个必要条件任何一条可避免死锁。最常用的方法是资源有序分配方式来破坏循环等待条件。

避免死锁方法：

（1）持有多个锁的话，锁的顺序要一致
（2）尽量避免锁的嵌套
（3）持有锁的方法尽量不要引用外部对象，可能外部对象也持有你的锁，会造成死锁