java死锁以及解决方案

分手后的思念是犯贱 2022-10-15 13:57 288阅读 0赞

**目录**

一、什么是死锁

二、代码实现一个死锁

三、如何判断是不是死锁

--------------------

# 一、什么是死锁 #

死锁是指两个或两个以上的进程在执行过程中，因争夺资源而造成的一种互相等待的现象，若无外力干涉那它们都将无法推进下去，如果系统资源充足，进程的资源请求都能够得到满足，死锁出现的可能性就很低，否则就会因争夺有限的资源而陷入死锁。

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L0FfYXJ0X3hpYW5n_size_16_color_FFFFFF_t_70][]

# 二、代码实现一个死锁 #

/**
    * 死锁发生，两个以上线程因争夺资源互相等待
    * 持有自己的锁，还妄图获得别人的锁
    */
    public class DeadLockDemo {
    
        public static void main(String[] args) {
            String LockA = "lockA";
            String LockB = "lockB";
    
            new Thread(new HoldLockThread(LockA, LockB), "t1").start();
            new Thread(new HoldLockThread(LockB, LockA), "t2").start();
    
        }
    }
    
    
    class HoldLockThread implements Runnable{
    
        private String lockA;
        private String lockB;
    
        public HoldLockThread(String lockA, String lockB){
            this.lockA = lockA;
            this.lockB = lockB;
        }
    
        @Override
        public void run() {
            synchronized (lockA){
                System.out.println(Thread.currentThread().getName() + "得到"+lockA+"锁尝试获得"+lockB+"锁");
                try {
                    Thread.sleep(200);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
                synchronized (lockB){
                    System.out.println(Thread.currentThread().getName() + "得到" +lockB);
                }
            }
    
        }
    }

# 三、如何判断是不是死锁 #

1.jps -l命令定位进程号

2.jstack找到死锁查看

![2021052516384219.png][]

E:\eclipseWorkspace\MySpringboot>jstack 9500
    2021-04-23 16:07:15
    Full thread dump Java HotSpot(TM) 64-Bit Server VM (25.131-b11 mixed mode):
    
    
    "DestroyJavaVM" #13 prio=5 os_prio=0 tid=0x0000000002b93800 nid=0x32d8 waiting on condition [0x0000000000000000]
       java.lang.Thread.State: RUNNABLE
    
    
    "t2" #12 prio=5 os_prio=0 tid=0x000000001a12f800 nid=0x4474 waiting for monitor entry [0x000000001b2ff000]
       java.lang.Thread.State: BLOCKED (on object monitor)
            at com.boot.security.server.myUtils.jiagou2021.locks.HoldLockThread.run(DeadLockDemo.java:45)
            - waiting to lock <0x00000000d6327610> (a java.lang.String)
            - locked <0x00000000d6327648> (a java.lang.String)
            at java.lang.Thread.run(Thread.java:748)
    
    
    "t1" #11 prio=5 os_prio=0 tid=0x000000001a290800 nid=0x43ec waiting for monitor entry [0x000000001b1ff000]
       java.lang.Thread.State: BLOCKED (on object monitor)
            at com.boot.security.server.myUtils.jiagou2021.locks.HoldLockThread.run(DeadLockDemo.java:45)
            - waiting to lock <0x00000000d6327648> (a java.lang.String)
            - locked <0x00000000d6327610> (a java.lang.String)
            at java.lang.Thread.run(Thread.java:748)
    
    
    "Service Thread" #10 daemon prio=9 os_prio=0 tid=0x00000000198ed000 nid=0xaa0 runnable [0x0000000000000000]
       java.lang.Thread.State: RUNNABLE
    
    
    "C1 CompilerThread2" #9 daemon prio=9 os_prio=2 tid=0x00000000198ec000 nid=0x7d4 waiting on condition [0x0000000000000000]
       java.lang.Thread.State: RUNNABLE
    
    
    "C2 CompilerThread1" #8 daemon prio=9 os_prio=2 tid=0x000000001987f800 nid=0x255c waiting on condition [0x0000000000000000]
       java.lang.Thread.State: RUNNABLE
    
    
    "C2 CompilerThread0" #7 daemon prio=9 os_prio=2 tid=0x0000000019831000 nid=0x17dc waiting on condition [0x0000000000000000]
       java.lang.Thread.State: RUNNABLE
    
    
    "Monitor Ctrl-Break" #6 daemon prio=5 os_prio=0 tid=0x00000000198fa000 nid=0x219c runnable [0x0000000019c2e000]
       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 <0x00000000d629f910> (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 <0x00000000d629f910> (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=0x0000000018d73800 nid=0x41c4 waiting on condition [0x0000000000000000]
       java.lang.Thread.State: RUNNABLE
    
    
    "Signal Dispatcher" #4 daemon prio=9 os_prio=2 tid=0x000000001799a800 nid=0x2954 runnable [0x0000000000000000]
       java.lang.Thread.State: RUNNABLE
    
    
    "Finalizer" #3 daemon prio=8 os_prio=1 tid=0x0000000017971800 nid=0x2d04 in Object.wait() [0x0000000018ccf000]
       java.lang.Thread.State: WAITING (on object monitor)
            at java.lang.Object.wait(Native Method)
            - waiting on <0x00000000d5d08ec8> (a java.lang.ref.ReferenceQueue$Lock)
            at java.lang.ref.ReferenceQueue.remove(ReferenceQueue.java:143)
            - locked <0x00000000d5d08ec8> (a java.lang.ref.ReferenceQueue$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=0x0000000017949800 nid=0x14cc in Object.wait() [0x0000000018bcf000]
       java.lang.Thread.State: WAITING (on object monitor)
            at java.lang.Object.wait(Native Method)
            - waiting on <0x00000000d5d06b68> (a java.lang.ref.Reference$Lock)
            at java.lang.Object.wait(Object.java:502)
            at java.lang.ref.Reference.tryHandlePending(Reference.java:191)
            - locked <0x00000000d5d06b68> (a java.lang.ref.Reference$Lock)
            at java.lang.ref.Reference$ReferenceHandler.run(Reference.java:153)
    
    
    "VM Thread" os_prio=2 tid=0x0000000017947800 nid=0x2f70 runnable
    
    
    "GC task thread#0 (ParallelGC)" os_prio=0 tid=0x0000000002bb1000 nid=0x4a64 runnable
    
    
    "GC task thread#1 (ParallelGC)" os_prio=0 tid=0x0000000002bb2800 nid=0x33cc runnable
    
    
    "GC task thread#2 (ParallelGC)" os_prio=0 tid=0x0000000002bb4800 nid=0x3bd4 runnable
    
    
    "GC task thread#3 (ParallelGC)" os_prio=0 tid=0x0000000002bb6000 nid=0x4e7c runnable
    
    
    "VM Periodic Task Thread" os_prio=2 tid=0x00000000198ee000 nid=0x20e8 waiting on condition
    
    
    JNI global references: 33
    
    
    
    
    Found one Java-level deadlock:
    =============================
    "t2":
      waiting to lock monitor 0x00000000179516b8 (object 0x00000000d6327610, a java.lang.String),
      which is held by "t1"
    "t1":
      waiting to lock monitor 0x0000000017950218 (object 0x00000000d6327648, a java.lang.String),
      which is held by "t2"
    
    
    Java stack information for the threads listed above:
    ===================================================
    "t2":
            at com.boot.security.server.myUtils.jiagou2021.locks.HoldLockThread.run(DeadLockDemo.java:45)
            - waiting to lock <0x00000000d6327610> (a java.lang.String)
            - locked <0x00000000d6327648> (a java.lang.String)
            at java.lang.Thread.run(Thread.java:748)
    "t1":
            at com.boot.security.server.myUtils.jiagou2021.locks.HoldLockThread.run(DeadLockDemo.java:45)
            - waiting to lock <0x00000000d6327648> (a java.lang.String)
            - locked <0x00000000d6327610> (a java.lang.String)
            at java.lang.Thread.run(Thread.java:748)
    
    
    Found 1 deadlock.

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L0FfYXJ0X3hpYW5n_size_16_color_FFFFFF_t_70 1][]

[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L0FfYXJ0X3hpYW5n_size_16_color_FFFFFF_t_70]: /images/20221014/7fd26bc679ad49b1ad43a7f657429c62.png
[2021052516384219.png]: /images/20221014/22f9461472714ef089fe7d4970844d39.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L0FfYXJ0X3hpYW5n_size_16_color_FFFFFF_t_70 1]: /images/20221014/6470736a4a864f518cc6904597b04c0c.png