JVM优化之：死锁构造与发现，以及解决思路

JVM优化之死锁构造与发现

我的博客园地址：其他的生产问题记录

死锁代码简单构造演示

java">package com.distributed.lock.utils;


import java.util.concurrent.TimeUnit;

public class ThreadDeadLock {

    public static void main(String[] args) {

        StringBuilder s1 = new StringBuilder();
        StringBuilder s2 = new StringBuilder();

        new Thread(new Runnable() {
            @Override
            public void run() {
                synchronized (s1) {
                    s1.append("a");
                    s2.append("1");
                    try {
                        TimeUnit.SECONDS.sleep(1);
                    } catch (InterruptedException e) {
                        throw new RuntimeException(e);
                    }

                    synchronized (s2){
                        s1.append("b");
                        s2.append("2");

                        System.out.println(s1);
                        System.out.println(s2);
                    }
                }

            }
        }).start();


        new Thread(new Runnable() {
            @Override
            public void run() {
                synchronized (s2) {
                    s1.append("c");
                    s2.append("3");

                    try {
                        TimeUnit.SECONDS.sleep(1);
                    } catch (InterruptedException e) {
                        throw new RuntimeException(e);
                    }

                    synchronized (s1) {
                        s1.append("d");
                        s2.append("4");

                        System.out.println(s2);
                        System.out.println(s1);
                    }
                }

            }
        }).start();

    }


}

死锁的查看

生产环境：在生产环境中也会出现死锁，主要在大型复杂的项目中，方法相互引用、并且加锁【加锁方式synchronized、ReentrantLock等】，此时是很难发现的，代码太多了。
查看工具：推荐使用jdk自带的简单查看工具jps + jstack（jvm stack trace），简单、安全。

jps:找到进程编号和相关的类信息

java">C:\Windows\system32>jps -l
10896
10808 sun.tools.jps.Jps
12456 org.jetbrains.jps.cmdline.Launcher
18600 com.distributed.lock.utils.ThreadDeadLock

2.发现死锁进程PID：如这里的18600（如何判断他就是死锁进程，这个需要开发人员自己判断这台服务器上运行了哪些应用）

3.判断这个进程是否发生了死锁：用jstack打印该进程的线程信息

java">C:\Windows\system32>jstack -help
Usage:
    jstack [-l] <pid>
        (to connect to running process)
    jstack -F [-m] [-l] <pid>
        (to connect to a hung process)
    jstack [-m] [-l] <executable> <core>
        (to connect to a core file)
    jstack [-m] [-l] [server_id@]<remote server IP or hostname>
        (to connect to a remote debug server)

Options:
    -F  to force a thread dump. Use when jstack <pid> does not respond (process is hung)
    -m  to print both java and native frames (mixed mode)
    -l  long listing. Prints additional information about locks
    -h or -help to print this help message

这里说的很明确了，我们就直接使用：jstack -l pid

java">C:\Windows\system32>jstack -l 18600
2023-11-25 11:04:15
Full thread dump Java HotSpot(TM) 64-Bit Server VM (25.291-b10 mixed mode):

"DestroyJavaVM" #16 prio=5 os_prio=0 tid=0x00000144e7cb5800 nid=0x40d4 waiting on condition [0x0000000000000000]
   java.lang.Thread.State: RUNNABLE

   Locked ownable synchronizers:
        - None

"Thread-1" #15 prio=5 os_prio=0 tid=0x00000146fbb15000 nid=0x2090 waiting for monitor entry [0x00000006df5fe000]
   java.lang.Thread.State: BLOCKED (on object monitor)
        at com.distributed.lock.utils.ThreadDeadLock$2.run(ThreadDeadLock.java:52)
        - waiting to lock <0x000001464cc06b40> (a java.lang.StringBuilder)
        - locked <0x000001464cc06b88> (a java.lang.StringBuilder)
        at java.lang.Thread.run(Thread.java:748)

   Locked ownable synchronizers:
        - None

"Thread-0" #14 prio=5 os_prio=0 tid=0x00000146fbb35000 nid=0x29c waiting for monitor entry [0x00000006df4ff000]
   java.lang.Thread.State: BLOCKED (on object monitor)
        at com.distributed.lock.utils.ThreadDeadLock$1.run(ThreadDeadLock.java:26)
        - waiting to lock <0x000001464cc06b88> (a java.lang.StringBuilder)
        - locked <0x000001464cc06b40> (a java.lang.StringBuilder)
        at java.lang.Thread.run(Thread.java:748)

   Locked ownable synchronizers:
        - None

"Service Thread" #13 daemon prio=9 os_prio=0 tid=0x00000146fbab1800 nid=0x3e90 runnable [0x0000000000000000]
   java.lang.Thread.State: RUNNABLE

   Locked ownable synchronizers:
        - None

"C1 CompilerThread3" #12 daemon prio=9 os_prio=2 tid=0x00000146fb9f9800 nid=0x34f8 waiting on condition [0x0000000000000000]
   java.lang.Thread.State: RUNNABLE

   Locked ownable synchronizers:
        - None

"C2 CompilerThread2" #11 daemon prio=9 os_prio=2 tid=0x00000146fb9f5000 nid=0x397c waiting on condition [0x0000000000000000]
   java.lang.Thread.State: RUNNABLE

   Locked ownable synchronizers:
        - None

"C2 CompilerThread1" #10 daemon prio=9 os_prio=2 tid=0x00000146fb9f4000 nid=0x3f44 waiting on condition [0x0000000000000000]
   java.lang.Thread.State: RUNNABLE

   Locked ownable synchronizers:
        - None

"C2 CompilerThread0" #9 daemon prio=9 os_prio=2 tid=0x00000146fb9dd000 nid=0x2548 waiting on condition [0x0000000000000000]
   java.lang.Thread.State: RUNNABLE

   Locked ownable synchronizers:
        - None

"JDWP Command Reader" #8 daemon prio=10 os_prio=0 tid=0x00000146fb9ca800 nid=0x3a1c runnable [0x0000000000000000]
   java.lang.Thread.State: RUNNABLE

   Locked ownable synchronizers:
        - None

"JDWP Event Helper Thread" #7 daemon prio=10 os_prio=0 tid=0x00000146fb9c7000 nid=0x2d8 runnable [0x0000000000000000]
   java.lang.Thread.State: RUNNABLE

   Locked ownable synchronizers:
        - None

"JDWP Transport Listener: dt_socket" #6 daemon prio=10 os_prio=0 tid=0x00000146f9c72800 nid=0x3ed8 runnable [0x0000000000000000]
   java.lang.Thread.State: RUNNABLE

   Locked ownable synchronizers:
        - None

"Attach Listener" #5 daemon prio=5 os_prio=2 tid=0x00000146f9c18000 nid=0x3c5c waiting on condition [0x0000000000000000]
   java.lang.Thread.State: RUNNABLE

   Locked ownable synchronizers:
        - None

"Signal Dispatcher" #4 daemon prio=9 os_prio=2 tid=0x00000146f9c17000 nid=0x20c4 runnable [0x0000000000000000]
   java.lang.Thread.State: RUNNABLE

   Locked ownable synchronizers:
        - None

"Finalizer" #3 daemon prio=8 os_prio=1 tid=0x00000146f9be9000 nid=0x4a9c in Object.wait() [0x00000006de8ff000]
   java.lang.Thread.State: WAITING (on object monitor)
        at java.lang.Object.wait(Native Method)
        - waiting on <0x000001464ca08ee0> (a java.lang.ref.ReferenceQueue$Lock)
        at java.lang.ref.ReferenceQueue.remove(ReferenceQueue.java:144)
        - locked <0x000001464ca08ee0> (a java.lang.ref.ReferenceQueue$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=2 tid=0x00000146f9bda000 nid=0x1b0c in Object.wait() [0x00000006de7ff000]
   java.lang.Thread.State: WAITING (on object monitor)
        at java.lang.Object.wait(Native Method)
        - waiting on <0x000001464ca06c00> (a java.lang.ref.Reference$Lock)
        at java.lang.Object.wait(Object.java:502)
        at java.lang.ref.Reference.tryHandlePending(Reference.java:191)
        - locked <0x000001464ca06c00> (a java.lang.ref.Reference$Lock)
        at java.lang.ref.Reference$ReferenceHandler.run(Reference.java:153)

   Locked ownable synchronizers:
        - None

"VM Thread" os_prio=2 tid=0x00000146f9bb0000 nid=0x4d04 runnable

"GC task thread#0 (ParallelGC)" os_prio=0 tid=0x00000144e7ccb000 nid=0x48ac runnable

"GC task thread#1 (ParallelGC)" os_prio=0 tid=0x00000144e7ccc800 nid=0x140 runnable

"GC task thread#2 (ParallelGC)" os_prio=0 tid=0x00000144e7cce000 nid=0x44b4 runnable

"GC task thread#3 (ParallelGC)" os_prio=0 tid=0x00000144e7cd0800 nid=0x48bc runnable

"GC task thread#4 (ParallelGC)" os_prio=0 tid=0x00000144e7cd2800 nid=0x1ba0 runnable

"GC task thread#5 (ParallelGC)" os_prio=0 tid=0x00000144e7cd3800 nid=0x4670 runnable

"GC task thread#6 (ParallelGC)" os_prio=0 tid=0x00000144e7cd6800 nid=0x34b4 runnable

"GC task thread#7 (ParallelGC)" os_prio=0 tid=0x00000144e7cd7800 nid=0x367c runnable

"VM Periodic Task Thread" os_prio=2 tid=0x00000146fbaea800 nid=0x7d4 waiting on condition

JNI global references: 1556


Found one Java-level deadlock:
=============================
"Thread-1":
  waiting to lock monitor 0x00000146f9be5bd8 (object 0x000001464cc06b40, a java.lang.StringBuilder),
  which is held by "Thread-0"
"Thread-0":
  waiting to lock monitor 0x00000146f9be8518 (object 0x000001464cc06b88, a java.lang.StringBuilder),
  which is held by "Thread-1"

Java stack information for the threads listed above:
===================================================
"Thread-1":
        at com.distributed.lock.utils.ThreadDeadLock$2.run(ThreadDeadLock.java:52)
        - waiting to lock <0x000001464cc06b40> (a java.lang.StringBuilder)
        - locked <0x000001464cc06b88> (a java.lang.StringBuilder)
        at java.lang.Thread.run(Thread.java:748)
"Thread-0":
        at com.distributed.lock.utils.ThreadDeadLock$1.run(ThreadDeadLock.java:26)
        - waiting to lock <0x000001464cc06b88> (a java.lang.StringBuilder)
        - locked <0x000001464cc06b40> (a java.lang.StringBuilder)
        at java.lang.Thread.run(Thread.java:748)

Found 1 deadlock.