1：通过jstack定位死锁信息

1.1：编写死锁代码

Lock lock1 = new ReentrantLock();
  Lock lock2 = new ReentrantLock();
  
  ExecutorService exectuorService = Executors.newFixedThreadPool(2);
  
  exectuorService.submit(() -> {
     lock1.lock();
     try{
         Thread.sleep(1000);
     }catch(Exception e){}
     try{}
     finally{
       lock1.unlock();
       lock2.unlock();
     }
  });
  exectuorService.submit(() -> {
     lock2.lock();
     try{
        Thread.sleep(1000);
     }catch(Exception e){}
     
     try{}
     finally{
         lock1.unlock();
         lock2.unlock();
     }
  });

1.2：查看死锁线程的pid

• jps查看死锁的线程pid
• 使用 jstack -l pid 查看死锁信息
• 通过打印信息我们可以找到发生死锁的代码是在哪个位置

"DestroyJavaVM" #13 prio=5 os_prio=31 tid=0x00007f9a1d8fe800 nid=0xd03 waiting on condition [0x0000000000000000]
   java.lang.Thread.State: RUNNABLE

   Locked ownable synchronizers:
 - None

"pool-1-thread-2" #12 prio=5 os_prio=31 tid=0x00007f9a1d8fe000 nid=0xa703 waiting on condition [0x000070000ff8e000]
   java.lang.Thread.State: WAITING (parking)
 at sun.misc.Unsafe.park(Native Method)
 - parking to wait for  <0x0000000795768cd8> (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.coco.util.SlideTimeUnit.lambda$main$1(SlideTimeUnit.java:63)
 at com.coco.util.SlideTimeUnit$$Lambda$2/565760380.run(Unknown Source)
 at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511)
 at java.util.concurrent.FutureTask.run(FutureTask.java:266)
 at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
 at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
 at java.lang.Thread.run(Thread.java:748)

   Locked ownable synchronizers:
 - <0x0000000795768d08> (a java.util.concurrent.locks.ReentrantLock$NonfairSync)
 - <0x0000000795a9e4e0> (a java.util.concurrent.ThreadPoolExecutor$Worker)

"pool-1-thread-1" #11 prio=5 os_prio=31 tid=0x00007f9a2082c800 nid=0xa803 waiting on condition [0x000070000fe8b000]
   java.lang.Thread.State: WAITING (parking)
 at sun.misc.Unsafe.park(Native Method)
 - parking to wait for  <0x0000000795768d08> (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.coco.util.SlideTimeUnit.lambda$main$0(SlideTimeUnit.java:49)
 at com.coco.util.SlideTimeUnit$$Lambda$1/596512129.run(Unknown Source)
 at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511)
 at java.util.concurrent.FutureTask.run(FutureTask.java:266)
 at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
 at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
 at java.lang.Thread.run(Thread.java:748)

   Locked ownable synchronizers:
 - <0x0000000795768cd8> (a java.util.concurrent.locks.ReentrantLock$NonfairSync)
 - <0x0000000795a9ba28> (a java.util.concurrent.ThreadPoolExecutor$Worker)

"Service Thread" #10 daemon prio=9 os_prio=31 tid=0x00007f9a2082c000 nid=0x4103 runnable [0x0000000000000000]
   java.lang.Thread.State: RUNNABLE

   Locked ownable synchronizers:
 - None

"C1 CompilerThread3" #9 daemon prio=9 os_prio=31 tid=0x00007f9a1e021800 nid=0x3f03 waiting on condition [0x0000000000000000]
   java.lang.Thread.State: RUNNABLE

2：通过Arthas工具定位死锁

2.1: 下载好Arthas的jar,然后运行

• 有一个 thread -b 就可以查看到死锁信息

[arthas@4182]$ thread -b
"pool-1-thread-2" Id=12 WAITING on java.util.concurrent.locks.ReentrantLock$NonfairSync@2cb8a9a3 owned by "pool-1-thread-1" Id=11
    at sun.misc.Unsafe.park(Native Method)
    -  waiting on java.util.concurrent.locks.ReentrantLock$NonfairSync@2cb8a9a3
    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$NonfairSync.lock(ReentrantLock.java:209)
    at java.util.concurrent.locks.ReentrantLock.lock(ReentrantLock.java:285)
    at com.coco.util.SlideTimeUnit.lambda$main$1(SlideTimeUnit.java:63)
    at com.coco.util.SlideTimeUnit$$Lambda$2/565760380.run(Unknown Source)
    at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511)
    at java.util.concurrent.FutureTask.run(FutureTask.java:266)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
    at java.lang.Thread.run(Thread.java:748)

    Number of locked synchronizers = 2
    - java.util.concurrent.ThreadPoolExecutor$Worker@6433a2
    - java.util.concurrent.locks.ReentrantLock$NonfairSync@3a855d13 <---- but blocks 1 other threads!

3. 通过 Jvisualvm 定位死锁

Jvisualvm 是一种自带的可视化工具，往往在在本地执行。

通过 Jvisualvm 命令打开软件，选中进程，进入线程视图，会给出死锁提示: