死锁及定位分析

原因

　　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相互等待的现象，如果无外力的干涉那它们都将无法推进下去，如果系统的资源充足，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

代码

public class DeadLockDemo {
    public static void main(String[] args) {
        String lockA = "lockA";
        String lockB = "lockB";

        DeadLockDemo deadLockDemo = new DeadLockDemo();
        Executor executor = Executors.newFixedThreadPool(2);
        executor.execute(() -> deadLockDemo.method(lockA, lockB));
        executor.execute(() -> deadLockDemo.method(lockB, lockA));

    }

    public void method(String lock1, String lock2) {
        synchronized (lock1) {
            System.out.println(Thread.currentThread().getName() + "--获取到：" + lock1 + "; 尝试获取：" + lock2);
            try {
                Thread.sleep(1000);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            synchronized (lock2) {
                System.out.println("获取到两把锁!");
            }
        }
    }
}

 定位分析

• jps -l 命令查定位进程号

HuandeMacBook-Air:study huanliu$ jps -l
56048 com.liuhuan.study.DeadLockDemo
484 
16308 org.jetbrains.jps.cmdline.Launcher
56089 sun.tools.jps.Jps
36329 
56047 org.jetbrains.jps.cmdline.Launcher

• jstack 进程号 找到死锁查看

HuandeMacBook-Air:study huanliu$ jstack 56048
2020-06-19 15:25:46
Full thread dump Java HotSpot(TM) 64-Bit Server VM (25.151-b12 mixed mode):

"Attach Listener" #15 daemon prio=9 os_prio=31 tid=0x00007fa2a9eb6800 nid=0x4c0b waiting on condition [0x0000000000000000]
   java.lang.Thread.State: RUNNABLE

"DestroyJavaVM" #14 prio=5 os_prio=31 tid=0x00007fa2a8bed800 nid=0xe03 waiting on condition [0x0000000000000000]
   java.lang.Thread.State: RUNNABLE

"pool-1-thread-2" #13 prio=5 os_prio=31 tid=0x00007fa2aa4d4800 nid=0x3a03 waiting for monitor entry [0x000070000e086000]
   java.lang.Thread.State: BLOCKED (on object monitor)
        at com.liuhuan.study.DeadLockDemo.method(DeadLockDemo.java:33)
        - waiting to lock <0x00000007960de9e0> (a java.lang.String)
        - locked <0x00000007960dea18> (a java.lang.String)
        at com.liuhuan.study.DeadLockDemo.lambda$main$1(DeadLockDemo.java:20)
        at com.liuhuan.study.DeadLockDemo$$Lambda$2/1176735295.run(Unknown Source)
        at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
        at java.lang.Thread.run(Thread.java:748)

"pool-1-thread-1" #12 prio=5 os_prio=31 tid=0x00007fa2a8beb800 nid=0x3d03 waiting for monitor entry [0x000070000df83000]
   java.lang.Thread.State: BLOCKED (on object monitor)
        at com.liuhuan.study.DeadLockDemo.method(DeadLockDemo.java:33)
        - waiting to lock <0x00000007960dea18> (a java.lang.String)
        - locked <0x00000007960de9e0> (a java.lang.String)
        at com.liuhuan.study.DeadLockDemo.lambda$main$0(DeadLockDemo.java:19)
        at com.liuhuan.study.DeadLockDemo$$Lambda$1/660879561.run(Unknown Source)
        at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
        at java.lang.Thread.run(Thread.java:748)

"Service Thread" #11 daemon prio=9 os_prio=31 tid=0x00007fa2a8bc5000 nid=0x3803 runnable [0x0000000000000000]
   java.lang.Thread.State: RUNNABLE

"C1 CompilerThread2" #10 daemon prio=9 os_prio=31 tid=0x00007fa2a8b8c000 nid=0x3703 waiting on condition [0x0000000000000000]
   java.lang.Thread.State: RUNNABLE

"C2 CompilerThread1" #9 daemon prio=9 os_prio=31 tid=0x00007fa2a8b8b800 nid=0x4103 waiting on condition [0x0000000000000000]
   java.lang.Thread.State: RUNNABLE

"C2 CompilerThread0" #8 daemon prio=9 os_prio=31 tid=0x00007fa2a8b8a800 nid=0x4303 waiting on condition [0x0000000000000000]
   java.lang.Thread.State: RUNNABLE

"JDWP Command Reader" #7 daemon prio=10 os_prio=31 tid=0x00007fa2a8819800 nid=0x3503 runnable [0x0000000000000000]
   java.lang.Thread.State: RUNNABLE

"JDWP Event Helper Thread" #6 daemon prio=10 os_prio=31 tid=0x00007fa2a8819000 nid=0x4603 runnable [0x0000000000000000]
   java.lang.Thread.State: RUNNABLE

"JDWP Transport Listener: dt_socket" #5 daemon prio=10 os_prio=31 tid=0x00007fa2a8818000 nid=0x3307 runnable [0x0000000000000000]
   java.lang.Thread.State: RUNNABLE

"Signal Dispatcher" #4 daemon prio=9 os_prio=31 tid=0x00007fa2a8816800 nid=0x3203 runnable [0x0000000000000000]
   java.lang.Thread.State: RUNNABLE

"Finalizer" #3 daemon prio=8 os_prio=31 tid=0x00007fa2a880c800 nid=0x5103 in Object.wait() [0x000070000d45f000]
   java.lang.Thread.State: WAITING (on object monitor)
        at java.lang.Object.wait(Native Method)
        - waiting on <0x0000000795588ec8> (a java.lang.ref.ReferenceQueue$Lock)
        at java.lang.ref.ReferenceQueue.remove(ReferenceQueue.java:143)
        - locked <0x0000000795588ec8> (a java.lang.ref.ReferenceQueue$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=31 tid=0x00007fa2aa01d000 nid=0x5303 in Object.wait() [0x000070000d35c000]
   java.lang.Thread.State: WAITING (on object monitor)
        at java.lang.Object.wait(Native Method)
        - waiting on <0x0000000795586b68> (a java.lang.ref.Reference$Lock)
        at java.lang.Object.wait(Object.java:502)
        at java.lang.ref.Reference.tryHandlePending(Reference.java:191)
        - locked <0x0000000795586b68> (a java.lang.ref.Reference$Lock)
        at java.lang.ref.Reference$ReferenceHandler.run(Reference.java:153)

"VM Thread" os_prio=31 tid=0x00007fa2a901a000 nid=0x2b03 runnable 

"GC task thread#0 (ParallelGC)" os_prio=31 tid=0x00007fa2aa002000 nid=0x1f07 runnable 

"GC task thread#1 (ParallelGC)" os_prio=31 tid=0x00007fa2aa005000 nid=0x2103 runnable 

"GC task thread#2 (ParallelGC)" os_prio=31 tid=0x00007fa2aa006000 nid=0x2303 runnable 

"GC task thread#3 (ParallelGC)" os_prio=31 tid=0x00007fa2aa006800 nid=0x2a03 runnable 

"VM Periodic Task Thread" os_prio=31 tid=0x00007fa2aa46a000 nid=0x3903 waiting on condition 

JNI global references: 2499


Found one Java-level deadlock:
=============================
"pool-1-thread-2":
  waiting to lock monitor 0x00007fa2a9021ca8 (object 0x00000007960de9e0, a java.lang.String),
  which is held by "pool-1-thread-1"
"pool-1-thread-1":
  waiting to lock monitor 0x00007fa2a901dc08 (object 0x00000007960dea18, a java.lang.String),
  which is held by "pool-1-thread-2"

Java stack information for the threads listed above:
===================================================
"pool-1-thread-2":
        at com.liuhuan.study.DeadLockDemo.method(DeadLockDemo.java:33)
        - waiting to lock <0x00000007960de9e0> (a java.lang.String)
        - locked <0x00000007960dea18> (a java.lang.String)
        at com.liuhuan.study.DeadLockDemo.lambda$main$1(DeadLockDemo.java:20)
        at com.liuhuan.study.DeadLockDemo$$Lambda$2/1176735295.run(Unknown Source)
        at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
        at java.lang.Thread.run(Thread.java:748)
"pool-1-thread-1":
        at com.liuhuan.study.DeadLockDemo.method(DeadLockDemo.java:33)
        - waiting to lock <0x00000007960dea18> (a java.lang.String)
        - locked <0x00000007960de9e0> (a java.lang.String)
        at com.liuhuan.study.DeadLockDemo.lambda$main$0(DeadLockDemo.java:19)
        at com.liuhuan.study.DeadLockDemo$$Lambda$1/660879561.run(Unknown Source)
        at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
        at java.lang.Thread.run(Thread.java:748)

Found 1 deadlock.