java程序死锁，3种方式快速找到死锁代码

程序员文章站 2022-03-12 16:16:19

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。 ......

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。