Java --- 01Java死锁

使用jstack检查死锁

import java.util.concurrent.BrokenBarrierException;
import java.util.concurrent.CyclicBarrier;

public class MyDeadThread {
    public static Object o1 = new Object();
    public static Object o2 = new Object();
    public static void main(String[] args) {
        CyclicBarrier barrier = new CyclicBarrier(2);
        new Thread(()->{
           synchronized (o1){
               try {
                   barrier.await();
               } catch (InterruptedException e) {
                   e.printStackTrace();
               } catch (BrokenBarrierException e) {
                   e.printStackTrace();
               }
//               latch.countDown();
//               try {
//                   latch.await();//此处不能这样用，latch是阻塞主线程的。应该用阻塞子线程的。
//               } catch (InterruptedException e) {
//                   e.printStackTrace();
//               }
               synchronized (o2){
                   System.out.println(Thread.currentThread().getName());
               }
           }
        }).start();
        new Thread(()->{
            synchronized (o2){
                try {
                    barrier.await();
                    int numberWaiting = barrier.getNumberWaiting();
                    int parties = barrier.getParties();
                    System.out.println("numberWaiting="+numberWaiting+"如果num为0说明barrier设计生效了");
                } catch (InterruptedException e) {
                    e.printStackTrace();
                } catch (BrokenBarrierException e) {
                    e.printStackTrace();
                }
                synchronized (o1){
                    System.out.println(Thread.currentThread().getName());
                }
            }
        }).start();
    }

}

　jstack查看

[root@master javatest]# jstack -l 2019
2020-10-24 11:50:03
Full thread dump Java HotSpot(TM) 64-Bit Server VM (25.221-b11 mixed mode):

"Attach Listener" #11 daemon prio=9 os_prio=0 tid=0x00007fd3f0001000 nid=0x809 waiting on condition [0x0000000000000000]
   java.lang.Thread.State: RUNNABLE

   Locked ownable synchronizers:
	- None

"DestroyJavaVM" #10 prio=5 os_prio=0 tid=0x00007fd418009000 nid=0x7e4 waiting on condition [0x0000000000000000]
   java.lang.Thread.State: RUNNABLE

   Locked ownable synchronizers:
	- None

"Thread-1" #9 prio=5 os_prio=0 tid=0x00007fd4180f7800 nid=0x7ee waiting for monitor entry [0x00007fd3f59bb000]
   java.lang.Thread.State: BLOCKED (on object monitor)
	at MyDeadLock.lambda$main$1(MyDeadLock.java:43)
	- waiting to lock <0x00000000f0a5baa8> (a java.lang.Object)
	- locked <0x00000000f0a5bab8> (a java.lang.Object)
	at MyDeadLock$$Lambda$2/135721597.run(Unknown Source)
	at java.lang.Thread.run(Thread.java:748)

   Locked ownable synchronizers:
	- None

"Thread-0" #8 prio=5 os_prio=0 tid=0x00007fd4180f5800 nid=0x7ed waiting for monitor entry [0x00007fd3f5abc000]
   java.lang.Thread.State: BLOCKED (on object monitor)
	at MyDeadLock.lambda$main$0(MyDeadLock.java:26)
	- waiting to lock <0x00000000f0a5bab8> (a java.lang.Object)
	- locked <0x00000000f0a5baa8> (a java.lang.Object)
	at MyDeadLock$$Lambda$1/1418481495.run(Unknown Source)
	at java.lang.Thread.run(Thread.java:748)

   Locked ownable synchronizers:
	- None

"Service Thread" #7 daemon prio=9 os_prio=0 tid=0x00007fd4180b4000 nid=0x7eb runnable [0x0000000000000000]
   java.lang.Thread.State: RUNNABLE

   Locked ownable synchronizers:
	- None

"C1 CompilerThread1" #6 daemon prio=9 os_prio=0 tid=0x00007fd4180b1000 nid=0x7ea waiting on condition [0x0000000000000000]
   java.lang.Thread.State: RUNNABLE

   Locked ownable synchronizers:
	- None

"C2 CompilerThread0" #5 daemon prio=9 os_prio=0 tid=0x00007fd4180af000 nid=0x7e9 waiting on condition [0x0000000000000000]
   java.lang.Thread.State: RUNNABLE

   Locked ownable synchronizers:
	- None

"Signal Dispatcher" #4 daemon prio=9 os_prio=0 tid=0x00007fd4180ad000 nid=0x7e8 runnable [0x0000000000000000]
   java.lang.Thread.State: RUNNABLE

   Locked ownable synchronizers:
	- None

"Finalizer" #3 daemon prio=8 os_prio=0 tid=0x00007fd41807c000 nid=0x7e7 in Object.wait() [0x00007fd4086fd000]
   java.lang.Thread.State: WAITING (on object monitor)
	at java.lang.Object.wait(Native Method)
	- waiting on <0x00000000f0a08ed8> (a java.lang.ref.ReferenceQueue$Lock)
	at java.lang.ref.ReferenceQueue.remove(ReferenceQueue.java:144)
	- locked <0x00000000f0a08ed8> (a java.lang.ref.ReferenceQueue$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=0 tid=0x00007fd418077800 nid=0x7e6 in Object.wait() [0x00007fd4087fe000]
   java.lang.Thread.State: WAITING (on object monitor)
	at java.lang.Object.wait(Native Method)
	- waiting on <0x00000000f0a06c00> (a java.lang.ref.Reference$Lock)
	at java.lang.Object.wait(Object.java:502)
	at java.lang.ref.Reference.tryHandlePending(Reference.java:191)
	- locked <0x00000000f0a06c00> (a java.lang.ref.Reference$Lock)
	at java.lang.ref.Reference$ReferenceHandler.run(Reference.java:153)

   Locked ownable synchronizers:
	- None

"VM Thread" os_prio=0 tid=0x00007fd41806e000 nid=0x7e5 runnable 

"VM Periodic Task Thread" os_prio=0 tid=0x00007fd4180b7000 nid=0x7ec waiting on condition 

JNI global references: 309


Found one Java-level deadlock:
=============================
"Thread-1":
  waiting to lock monitor 0x00007fd3fc004e28 (object 0x00000000f0a5baa8, a java.lang.Object),
  which is held by "Thread-0"
"Thread-0":
  waiting to lock monitor 0x00007fd3fc0062c8 (object 0x00000000f0a5bab8, a java.lang.Object),
  which is held by "Thread-1"

Java stack information for the threads listed above:
===================================================
"Thread-1":
	at MyDeadLock.lambda$main$1(MyDeadLock.java:43)
	- waiting to lock <0x00000000f0a5baa8> (a java.lang.Object)
	- locked <0x00000000f0a5bab8> (a java.lang.Object)
	at MyDeadLock$$Lambda$2/135721597.run(Unknown Source)
	at java.lang.Thread.run(Thread.java:748)
"Thread-0":
	at MyDeadLock.lambda$main$0(MyDeadLock.java:26)
	- waiting to lock <0x00000000f0a5bab8> (a java.lang.Object)
	- locked <0x00000000f0a5baa8> (a java.lang.Object)
	at MyDeadLock$$Lambda$1/1418481495.run(Unknown Source)
	at java.lang.Thread.run(Thread.java:748)

Found 1 deadlock.

　　

参考：
https://docs.oracle.com/javase/8/docs/api/