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一个简单的死锁例子

yellowone 2022-12-22 阅读 196
java.netJavaSpark大数据


代码如下：

package com.example.demo.service;

import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;

/**
 * @author Dongguabai
 * @description
 * @date 2021-03-28 12:18
 */
public class Test2 {

    static Lock lock1 = new ReentrantLock();
    static Lock lock2 = new ReentrantLock();

    public static void main(String[] args) {
        new Thread(()->{
            lock1.lock();
            System.out.println(Thread.currentThread()+"】】已经获取lock1准备获取lock2");
            lock2.lock();
            lock1.unlock();
            lock2.unlock();
        }).start();


        new Thread(()->{
            lock2.lock();
            System.out.println(Thread.currentThread()+"】】已经获取lock2准备获取lock1");
            lock1.lock();
            lock1.unlock();
            lock2.unlock();
        }).start();
    }
}

通过 ​​jstack​​ 很容易可以看出来：

➜  ~ jps           
560 NutstoreGUI
4642 Jps
4531 Launcher
4532 Test2
4264 
4330 RemoteMavenServer
➜  ~ jstack -l 4532 > 1.txt

2021-03-28 12:24:40
Full thread dump Java HotSpot(TM) 64-Bit Server VM (25.201-b09 mixed mode):

"Attach Listener" #14 daemon prio=9 os_prio=31 tid=0x00007f87a485b000 nid=0x5803 waiting on condition [0x0000000000000000]
   java.lang.Thread.State: RUNNABLE

   Locked ownable synchronizers:
  - None

"DestroyJavaVM" #13 prio=5 os_prio=31 tid=0x00007f879e80e800 nid=0x1003 waiting on condition [0x0000000000000000]
   java.lang.Thread.State: RUNNABLE

   Locked ownable synchronizers:
  - None

"Thread-1" #12 prio=5 os_prio=31 tid=0x00007f87a2119000 nid=0x5703 waiting on condition [0x000070000f26c000]
   java.lang.Thread.State: WAITING (parking)
  at sun.misc.Unsafe.park(Native Method)
  - parking to wait for  <0x00000007957e1a60> (a java.util.concurrent.locks.ReentrantLock$NonfairSync)
  at java.util.concurrent.locks.LockSupport.park(LockSupport.java:175)
  at java.util.concurrent.locks.AbstractQueuedSynchronizer.parkAndCheckInterrupt(AbstractQueuedSynchronizer.java:836)
  at java.util.concurrent.locks.AbstractQueuedSynchronizer.acquireQueued(AbstractQueuedSynchronizer.java:870)
  at java.util.concurrent.locks.AbstractQueuedSynchronizer.acquire(AbstractQueuedSynchronizer.java:1199)
  at java.util.concurrent.locks.ReentrantLock$NonfairSync.lock(ReentrantLock.java:209)
  at java.util.concurrent.locks.ReentrantLock.lock(ReentrantLock.java:285)
  at com.example.demo.service.Test2.lambda$main$1(Test2.java:29)
  at com.example.demo.service.Test2$$Lambda$2/193064360.run(Unknown Source)
  at java.lang.Thread.run(Thread.java:748)

   Locked ownable synchronizers:
  - <0x00000007957e1a90> (a java.util.concurrent.locks.ReentrantLock$NonfairSync)

"Thread-0" #11 prio=5 os_prio=31 tid=0x00007f87a2118000 nid=0xa803 waiting on condition [0x000070000f169000]
   java.lang.Thread.State: WAITING (parking)
  at sun.misc.Unsafe.park(Native Method)
  - parking to wait for  <0x00000007957e1a90> (a java.util.concurrent.locks.ReentrantLock$NonfairSync)
  at java.util.concurrent.locks.LockSupport.park(LockSupport.java:175)
  at java.util.concurrent.locks.AbstractQueuedSynchronizer.parkAndCheckInterrupt(AbstractQueuedSynchronizer.java:836)
  at java.util.concurrent.locks.AbstractQueuedSynchronizer.acquireQueued(AbstractQueuedSynchronizer.java:870)
  at java.util.concurrent.locks.AbstractQueuedSynchronizer.acquire(AbstractQueuedSynchronizer.java:1199)
  at java.util.concurrent.locks.ReentrantLock$NonfairSync.lock(ReentrantLock.java:209)
  at java.util.concurrent.locks.ReentrantLock.lock(ReentrantLock.java:285)
  at com.example.demo.service.Test2.lambda$main$0(Test2.java:20)
  at com.example.demo.service.Test2$$Lambda$1/94438417.run(Unknown Source)
  at java.lang.Thread.run(Thread.java:748)

   Locked ownable synchronizers:
  - <0x00000007957e1a60> (a java.util.concurrent.locks.ReentrantLock$NonfairSync)

"Service Thread" #10 daemon prio=9 os_prio=31 tid=0x00007f87a485a800 nid=0x4103 runnable [0x0000000000000000]
   java.lang.Thread.State: RUNNABLE

   Locked ownable synchronizers:
  - None

"C1 CompilerThread3" #9 daemon prio=9 os_prio=31 tid=0x00007f879f882800 nid=0x4303 waiting on condition [0x0000000000000000]
   java.lang.Thread.State: RUNNABLE

   Locked ownable synchronizers:
  - None

"C2 CompilerThread2" #8 daemon prio=9 os_prio=31 tid=0x00007f879f882000 nid=0x3e03 waiting on condition [0x0000000000000000]
   java.lang.Thread.State: RUNNABLE

   Locked ownable synchronizers:
  - None

"C2 CompilerThread1" #7 daemon prio=9 os_prio=31 tid=0x00007f879f880800 nid=0x3d03 waiting on condition [0x0000000000000000]
   java.lang.Thread.State: RUNNABLE

   Locked ownable synchronizers:
  - None

"C2 CompilerThread0" #6 daemon prio=9 os_prio=31 tid=0x00007f879f87f800 nid=0x3c03 waiting on condition [0x0000000000000000]
   java.lang.Thread.State: RUNNABLE

   Locked ownable synchronizers:
  - None

"Monitor Ctrl-Break" #5 daemon prio=5 os_prio=31 tid=0x00007f879f87e000 nid=0x4703 runnable [0x000070000ea54000]
   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 <0x0000000795858900> (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 <0x0000000795858900> (a java.io.InputStreamReader)
  at java.io.BufferedReader.readLine(BufferedReader.java:389)
  at com.intellij.rt.execution.application.AppMainV2$1.run(AppMainV2.java:64)

   Locked ownable synchronizers:
  - None

"Signal Dispatcher" #4 daemon prio=9 os_prio=31 tid=0x00007f879e808800 nid=0x3a03 runnable [0x0000000000000000]
   java.lang.Thread.State: RUNNABLE

   Locked ownable synchronizers:
  - None

"Finalizer" #3 daemon prio=8 os_prio=31 tid=0x00007f87a1823800 nid=0x4f03 in Object.wait() [0x000070000e748000]
   java.lang.Thread.State: WAITING (on object monitor)
  at java.lang.Object.wait(Native Method)
  - waiting on <0x0000000795588ed0> (a java.lang.ref.ReferenceQueue$Lock)
  at java.lang.ref.ReferenceQueue.remove(ReferenceQueue.java:144)
  - locked <0x0000000795588ed0> (a java.lang.ref.ReferenceQueue$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=31 tid=0x00007f87a2013800 nid=0x5003 in Object.wait() [0x000070000e645000]
   java.lang.Thread.State: WAITING (on object monitor)
  at java.lang.Object.wait(Native Method)
  - waiting on <0x0000000795586bf8> (a java.lang.ref.Reference$Lock)
  at java.lang.Object.wait(Object.java:502)
  at java.lang.ref.Reference.tryHandlePending(Reference.java:191)
  - locked <0x0000000795586bf8> (a java.lang.ref.Reference$Lock)
  at java.lang.ref.Reference$ReferenceHandler.run(Reference.java:153)

   Locked ownable synchronizers:
  - None

"VM Thread" os_prio=31 tid=0x00007f87a200d000 nid=0x3003 runnable 

"GC task thread#0 (ParallelGC)" os_prio=31 tid=0x00007f87a180b800 nid=0x2507 runnable 

"GC task thread#1 (ParallelGC)" os_prio=31 tid=0x00007f87a080b000 nid=0x2403 runnable 

"GC task thread#2 (ParallelGC)" os_prio=31 tid=0x00007f879f00c800 nid=0x2203 runnable 

"GC task thread#3 (ParallelGC)" os_prio=31 tid=0x00007f87a180c000 nid=0x2a03 runnable 

"GC task thread#4 (ParallelGC)" os_prio=31 tid=0x00007f87a180c800 nid=0x5303 runnable 

"GC task thread#5 (ParallelGC)" os_prio=31 tid=0x00007f87a180d800 nid=0x5203 runnable 

"GC task thread#6 (ParallelGC)" os_prio=31 tid=0x00007f87a180e000 nid=0x2d03 runnable 

"GC task thread#7 (ParallelGC)" os_prio=31 tid=0x00007f87a180e800 nid=0x2e03 runnable 

"VM Periodic Task Thread" os_prio=31 tid=0x00007f87a210c000 nid=0x5503 waiting on condition 

JNI global references: 320


Found one Java-level deadlock:
=============================
"Thread-1":
  waiting for ownable synchronizer 0x00000007957e1a60, (a java.util.concurrent.locks.ReentrantLock$NonfairSync),
  which is held by "Thread-0"
"Thread-0":
  waiting for ownable synchronizer 0x00000007957e1a90, (a java.util.concurrent.locks.ReentrantLock$NonfairSync),
  which is held by "Thread-1"

Java stack information for the threads listed above:
===================================================
"Thread-1":
  at sun.misc.Unsafe.park(Native Method)
  - parking to wait for  <0x00000007957e1a60> (a java.util.concurrent.locks.ReentrantLock$NonfairSync)
  at java.util.concurrent.locks.LockSupport.park(LockSupport.java:175)
  at java.util.concurrent.locks.AbstractQueuedSynchronizer.parkAndCheckInterrupt(AbstractQueuedSynchronizer.java:836)
  at java.util.concurrent.locks.AbstractQueuedSynchronizer.acquireQueued(AbstractQueuedSynchronizer.java:870)
  at java.util.concurrent.locks.AbstractQueuedSynchronizer.acquire(AbstractQueuedSynchronizer.java:1199)
  at java.util.concurrent.locks.ReentrantLock$NonfairSync.lock(ReentrantLock.java:209)
  at java.util.concurrent.locks.ReentrantLock.lock(ReentrantLock.java:285)
  at com.example.demo.service.Test2.lambda$main$1(Test2.java:29)
  at com.example.demo.service.Test2$$Lambda$2/193064360.run(Unknown Source)
  at java.lang.Thread.run(Thread.java:748)
"Thread-0":
  at sun.misc.Unsafe.park(Native Method)
  - parking to wait for  <0x00000007957e1a90> (a java.util.concurrent.locks.ReentrantLock$NonfairSync)
  at java.util.concurrent.locks.LockSupport.park(LockSupport.java:175)
  at java.util.concurrent.locks.AbstractQueuedSynchronizer.parkAndCheckInterrupt(AbstractQueuedSynchronizer.java:836)
  at java.util.concurrent.locks.AbstractQueuedSynchronizer.acquireQueued(AbstractQueuedSynchronizer.java:870)
  at java.util.concurrent.locks.AbstractQueuedSynchronizer.acquire(AbstractQueuedSynchronizer.java:1199)
  at java.util.concurrent.locks.ReentrantLock$NonfairSync.lock(ReentrantLock.java:209)
  at java.util.concurrent.locks.ReentrantLock.lock(ReentrantLock.java:285)
  at com.example.demo.service.Test2.lambda$main$0(Test2.java:20)
  at com.example.demo.service.Test2$$Lambda$1/94438417.run(Unknown Source)
  at java.lang.Thread.run(Thread.java:748)

Found 1 deadlock.

可以看到发生了死锁。两个线程在互相等待对方释放锁。
平时要注意加锁顺序和对结果的互相依赖，或者加锁增加超时时间。


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