Java程序死锁，3种方式快速找到死锁代码

短命女 2022-10-02 00:56 55阅读 0赞

[2019独角兽企业重金招聘Python工程师标准>>> ][2019_Python_] ![hot3.png][]

java程序中出现死锁问题，如果不了解排查方法，是束手无策的，今天咱们用三种方法找到死锁问题。

#### 运行下面代码 ####

package com.jvm.visualvm;
    
    /**
     * <a href="http://www.itsoku.com/archives">Java干货铺子,只生产干货，公众号：javacode2018</a>
     */
    public class Demo4 {
    
        public static void main(String[] args) {
            User u1 = new User("u1");
            User u2 = new User("u2");
            Thread thread1 = new Thread(new SynAddRunalbe(u1, u2, 1, 2, true));
            thread1.setName("thread1");
            thread1.start();
            Thread thread2 = new Thread(new SynAddRunalbe(u1, u2, 2, 1, false));
            thread2.setName("thread2");
            thread2.start();
        }
    
        /**
         * 线程死锁等待演示
         */
        public static class SynAddRunalbe implements Runnable {
            User u1, u2;
            int a, b;
            boolean flag;
    
            public SynAddRunalbe(User u1, User u2, int a, int b, boolean flag) {
                this.u1 = u1;
                this.u2 = u2;
                this.a = a;
                this.b = b;
                this.flag = flag;
            }
    
            @Override
            public void run() {
                try {
                    if (flag) {
                        synchronized (u1) {
                            Thread.sleep(100);
                            synchronized (u2) {
                                System.out.println(a + b);
                            }
                        }
                    } else {
                        synchronized (u2) {
                            Thread.sleep(100);
                            synchronized (u1) {
                                System.out.println(a + b);
                            }
                        }
                    }
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        }
    
        public static class User {
            private String name;
    
            public String getName() {
                return name;
            }
    
            public void setName(String name) {
                this.name = name;
            }
    
            public User(String name) {
                this.name = name;
            }
    
            @Override
            public String toString() {
                return "User{" +
                        "name='" + name + '\'' +
                        '}';
            }
        }
    }

程序中：thread1持有u1的锁，thread2持有u2的锁，thread1等待获取u2的锁，thread2等待获取u1的锁，相互需要获取的锁都被对方持有者，造成了死锁。程序运行中一直无法结束。

通过jdk工具jps、jstack排查死锁问题 jps、jstack都是jdk提供的命令工具，方便用户排查程序的一些问题。更详细的用法见文档最后。

步骤一：使用jsp查找程序进行 jps：jdk提供的一个工具，可以查看到正在运行的java进程

C:\Users\Think>jps -l
    5824 com.jvm.visualvm.Demo4

步骤二：使用jstack查看线程堆栈信息 jstack：jdk提供的一个工具，可以查看java进程中线程堆栈信息。更详细的用法见文档最后。

C:\Users\Think>jstack 5824
    2019-06-04 15:34:37
    Full thread dump Java HotSpot(TM) 64-Bit Server VM (25.121-b13 mixed mode):
    
    "DestroyJavaVM" #14 prio=5 os_prio=0 tid=0x0000000002cf4000 nid=0x9fd8 waiting on condition [0x0000000000000000]
       java.lang.Thread.State: RUNNABLE
    
    "thread2" #13 prio=5 os_prio=0 tid=0x000000002884d800 nid=0x40c4 waiting for monitor entry [0x00000000292ce000]
       java.lang.Thread.State: BLOCKED (on object monitor)
            at com.jvm.visualvm.Demo4$SynAddRunalbe.run(Demo4.java:49)
            - waiting to lock <0x00000007173d4178> (a com.jvm.visualvm.Demo4$User)
            - locked <0x00000007173d41b8> (a com.jvm.visualvm.Demo4$User)
            at java.lang.Thread.run(Thread.java:745)
    
    "thread1" #12 prio=5 os_prio=0 tid=0x000000002885b800 nid=0x99c0 waiting for monitor entry [0x00000000291cf000]
       java.lang.Thread.State: BLOCKED (on object monitor)
            at com.jvm.visualvm.Demo4$SynAddRunalbe.run(Demo4.java:42)
            - waiting to lock <0x00000007173d41b8> (a com.jvm.visualvm.Demo4$User)
            - locked <0x00000007173d4178> (a com.jvm.visualvm.Demo4$User)
            at java.lang.Thread.run(Thread.java:745)
    
    "Service Thread" #11 daemon prio=9 os_prio=0 tid=0x0000000027dd9000 nid=0x7f80 runnable [0x0000000000000000]
       java.lang.Thread.State: RUNNABLE
    
    "C1 CompilerThread3" #10 daemon prio=9 os_prio=2 tid=0x0000000027d80800 nid=0x3b94 waiting on condition [0x0000000000000000]
       java.lang.Thread.State: RUNNABLE
    
    "C2 CompilerThread2" #9 daemon prio=9 os_prio=2 tid=0x0000000027d7c000 nid=0x4c7c waiting on condition [0x0000000000000000]
       java.lang.Thread.State: RUNNABLE
    
    "C2 CompilerThread1" #8 daemon prio=9 os_prio=2 tid=0x0000000027d7b000 nid=0x8f4c waiting on condition [0x0000000000000000]
       java.lang.Thread.State: RUNNABLE
    
    "C2 CompilerThread0" #7 daemon prio=9 os_prio=2 tid=0x0000000027d73000 nid=0x9094 waiting on condition [0x0000000000000000]
       java.lang.Thread.State: RUNNABLE
    
    "Monitor Ctrl-Break" #6 daemon prio=5 os_prio=0 tid=0x0000000027d0a800 nid=0x647c runnable [0x00000000282ce000]
       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 <0x0000000717449cd8> (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 <0x0000000717449cd8> (a java.io.InputStreamReader)
            at java.io.BufferedReader.readLine(BufferedReader.java:389)
            at com.intellij.rt.execution.application.AppMainV2$1.run(AppMainV2.java:64)
    
    "Attach Listener" #5 daemon prio=5 os_prio=2 tid=0x0000000027b61000 nid=0x7cf8 waiting on condition [0x0000000000000000]
       java.lang.Thread.State: RUNNABLE
    
    "Signal Dispatcher" #4 daemon prio=9 os_prio=2 tid=0x0000000027b5f800 nid=0x94f4 runnable [0x0000000000000000]
       java.lang.Thread.State: RUNNABLE
    
    "Finalizer" #3 daemon prio=8 os_prio=1 tid=0x0000000027af1800 nid=0x9960 in Object.wait() [0x0000000027fce000]
       java.lang.Thread.State: WAITING (on object monitor)
            at java.lang.Object.wait(Native Method)
            - waiting on <0x0000000717188ec8> (a java.lang.ref.ReferenceQueue$Lock)
            at java.lang.ref.ReferenceQueue.remove(ReferenceQueue.java:143)
            - locked <0x0000000717188ec8> (a java.lang.ref.ReferenceQueue$Lock)
            at java.lang.ref.ReferenceQueue.remove(ReferenceQueue.java:164)
            at java.lang.ref.Finalizer$FinalizerThread.run(Finalizer.java:209)
    
    "Reference Handler" #2 daemon prio=10 os_prio=2 tid=0x0000000002deb000 nid=0xb2bc in Object.wait() [0x0000000027acf000]
       java.lang.Thread.State: WAITING (on object monitor)
            at java.lang.Object.wait(Native Method)
            - waiting on <0x0000000717186b68> (a java.lang.ref.Reference$Lock)
            at java.lang.Object.wait(Object.java:502)
            at java.lang.ref.Reference.tryHandlePending(Reference.java:191)
            - locked <0x0000000717186b68> (a java.lang.ref.Reference$Lock)
            at java.lang.ref.Reference$ReferenceHandler.run(Reference.java:153)
    
    "VM Thread" os_prio=2 tid=0x0000000025be9000 nid=0xaa90 runnable
    
    "GC task thread#0 (ParallelGC)" os_prio=0 tid=0x0000000002d0a000 nid=0x3fc0 runnable
    
    "GC task thread#1 (ParallelGC)" os_prio=0 tid=0x0000000002d0b800 nid=0x9cf8 runnable
    
    "GC task thread#2 (ParallelGC)" os_prio=0 tid=0x0000000002d0d000 nid=0x51c runnable
    
    "GC task thread#3 (ParallelGC)" os_prio=0 tid=0x0000000002d0e800 nid=0x24d0 runnable
    
    "GC task thread#4 (ParallelGC)" os_prio=0 tid=0x0000000002d12000 nid=0x618c runnable
    
    "GC task thread#5 (ParallelGC)" os_prio=0 tid=0x0000000002d13000 nid=0x5550 runnable
    
    "GC task thread#6 (ParallelGC)" os_prio=0 tid=0x0000000002d16000 nid=0x8994 runnable
    
    "GC task thread#7 (ParallelGC)" os_prio=0 tid=0x0000000002d17800 nid=0x39cc runnable
    
    "VM Periodic Task Thread" os_prio=2 tid=0x0000000027dd9800 nid=0x5294 waiting on condition
    
    JNI global references: 33
    
    
    Found one Java-level deadlock:
    =============================
    "thread2":
      waiting to lock monitor 0x0000000028846468 (object 0x00000007173d4178, a com.jvm.visualvm.Demo4$User),
      which is held by "thread1"
    "thread1":
      waiting to lock monitor 0x0000000025bf0bb8 (object 0x00000007173d41b8, a com.jvm.visualvm.Demo4$User),
      which is held by "thread2"
    
    Java stack information for the threads listed above:
    ===================================================
    "thread2":
            at com.jvm.visualvm.Demo4$SynAddRunalbe.run(Demo4.java:49)
            - waiting to lock <0x00000007173d4178> (a com.jvm.visualvm.Demo4$User)
            - locked <0x00000007173d41b8> (a com.jvm.visualvm.Demo4$User)
            at java.lang.Thread.run(Thread.java:745)
    "thread1":
            at com.jvm.visualvm.Demo4$SynAddRunalbe.run(Demo4.java:42)
            - waiting to lock <0x00000007173d41b8> (a com.jvm.visualvm.Demo4$User)
            - locked <0x00000007173d4178> (a com.jvm.visualvm.Demo4$User)
            at java.lang.Thread.run(Thread.java:745)
    
    Found 1 deadlock.
    从上面的堆栈信息中我们可以发现这个内容：“Found one Java-level deadlock”，表示程序中发现了一个死锁，后面包含跟多详细的信息，重点下面：
    
    Java stack information for the threads listed above:
    ===================================================
    "thread2":
            at com.jvm.visualvm.Demo4$SynAddRunalbe.run(Demo4.java:49)
            - waiting to lock <0x00000007173d4178> (a com.jvm.visualvm.Demo4$User)
            - locked <0x00000007173d41b8> (a com.jvm.visualvm.Demo4$User)
            at java.lang.Thread.run(Thread.java:745)
    "thread1":
            at com.jvm.visualvm.Demo4$SynAddRunalbe.run(Demo4.java:42)
            - waiting to lock <0x00000007173d41b8> (a com.jvm.visualvm.Demo4$User)
            - locked <0x00000007173d4178> (a com.jvm.visualvm.Demo4$User)
            at java.lang.Thread.run(Thread.java:745)

可以死锁的代码是在Demo4.java的49行和42行，此时我们就可以去优化代码，解决死锁问题。

## 通过jdk提供的工具jconsole排查死锁问题 ##

> jconsole：jdk提供的一个可视化的工具，方便排查程序的一些问题，如：程序内存溢出、死锁问题等等。更详细的用法见文档最后。
> 
> jconsole位于jdk的bin目录中

### 步骤一：打开jconsole.exe ###

![1240][]

可以看到我们的程序，点击连接。

### 步骤二：在jconsole窗口中查看线程堆栈信息 ###

![1240 1][]

### 步骤三：堆栈中查看到死锁信息 ###

点击“检测死锁”，可以看到程序死锁信息。

![1240 2][]

![1240 3][]

上图中可以看到详细的死锁信息，和jstack中信息类似。

## 通过jdk提供的工具VisualVM排查死锁问题 ##

> VisualVM：jdk提供的一个非常强大的排查java程序问题的一个工具，可以监控程序的性能、查看jvm配置信息、堆快照、线程堆栈信息。算是程序优化的必备工具。
> 
> 工具位于jdk的bin目录中。

### 步骤一：打开VisualVM.exe ###

![1240 4][]

### 步骤二：在visualvm中查看我们的目标程序 ###

> 目标程序在visualvm左侧窗口中，双击即可打开。

![1240 5][]

### 步骤三：切换到“线程”窗口 ###

![1240 6][]

### 步骤四：查看堆栈信息 ###

在线程窗口中点击“线程Dump”按钮

![1240 7][]

可以看到产生了一个线程堆栈快照

![1240 8][]

线程堆栈快照的信息和jstack查看到的信息一样，即可发现死锁代码。

## 总结 ##

程序中介绍了3中排查死锁的方法，使用到的都是jdk提供给我们的工具，这些工具对于我们优化程序来说，是非常好的，我们一定要掌握。

转载于:https://my.oschina.net/u/4142269/blog/3058798

[2019_Python_]: https://my.oschina.net/u/2663968/blog/3061697
[hot3.png]: /images/20220113/a8c4a4a58c064fe0803532eb43f8aea6.png
[1240]: /images/20220113/46054d54dc344b4cbca884c7b6068857.png
[1240 1]: /images/20220113/89ef4027ee674f31bf672cc60cda4759.png
[1240 2]: /images/20220113/ec64daddd32346d5a2af17d9e8cbfd89.png
[1240 3]: /images/20220113/8c771d2af4f94896929ea25ce0c874ab.png
[1240 4]: /images/20220113/7caee9280ab6445da79df466210df293.png
[1240 5]: /images/20220113/5fdaa0fea73949f89d0b17dab61fbb23.png
[1240 6]: /images/20220113/e9e3921994bf40f2aad8eec8ce90d6e4.png
[1240 7]: /images/20220113/d14ab21c75d0409493fcac57eac142fb.png
[1240 8]: /images/20220113/383011c900f54f07b12476f2614282ab.png