java死锁（Java-level deadlock）-百木园

java-level deadlock

如下代码可以模拟java死锁。注意：当出现死锁时，应用程序是无响应的。错误信息：

Found one Java-level deadlock:
=============================
\"Thread-1\":
waiting to lock monitor 0x000000001c773158 (object 0x000000076bbc06b8, a java.util.concurrent.Concurren
tHashMap),
which is held by \"Thread-0\"
\"Thread-0\":
waiting to lock monitor 0x000000001c774548 (object 0x000000076bbc06f8, a java.lang.Object),
which is held by \"Thread-1\"

deadlock demo及deadlock信息

上代码：

import java.util.concurrent.ConcurrentHashMap;
import static java.util.concurrent.TimeUnit.SECONDS;

public class TestDeadlockMain {

    private static final ConcurrentHashMap<String, String> concurrentHashMap1 = new ConcurrentHashMap<>(128);
    private static final Object concurrentHashMap2 = new Object();

    public static void main(String[] args) {
        new Thread(() -> {
            synchronized (concurrentHashMap1) {

                // 模拟逻辑执行
                try {
                    SECONDS.sleep(1L);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }

                synchronized (concurrentHashMap2) {
                    // 模拟逻辑执行
                    System.out.println(\"test deadlock\");
                }
            }
        }).start();
        new Thread(() -> {
            synchronized (concurrentHashMap2) {
                synchronized (concurrentHashMap1) {
                    // 模拟逻辑执行
                    try {
                        SECONDS.sleep(1L);
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                }
            }
        }).start();
        new Thread(()->{
            while (true){
                System.out.println(System.currentTimeMillis());
                try {
                    SECONDS.sleep(1);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        }).start();
    }

}

运行程序，通过控制台日志是无法看到死锁信息的。只能看到第三个线程在间隔1s不停的打日志，却无法看到另外两个线程在干啥。

如果是所调用的程序有用户界面的话，就会看到长时间无响应或超时的现象。

至于这个demo呢，我们可以借助IDEA的Terminal窗口。执行jps -l 命令，找到当前执行的java程序的进程pid。接下来执行 jstack pid 命令，查看JVM里的线程快照信息。

如下贴出来Terminal窗口的内容：

D:\\SourceProject\\account\\target\\test-classes\\com\\emaxcard\\jvm>jps -l
24912
21556 org.jetbrains.jps.cmdline.Launcher
28840 com.emaxcard.jvm.TestDeadlockMain
30328 sun.tools.jps.Jps
13644 org.jetbrains.idea.maven.server.RemoteMavenServer

D:\\SourceProject\\account\\target\\test-classes\\com\\emaxcard\\jvm>jstack 28840
2022-08-24 20:56:11
Full thread dump Java HotSpot(TM) 64-Bit Server VM (25.40-b25 mixed mode):

\"DestroyJavaVM\" #14 prio=5 os_prio=0 tid=0x0000000002a58800 nid=0x6bf4 waiting on condition [0x0000000000
000000]
   java.lang.Thread.State: RUNNABLE

\"Thread-1\" #13 prio=5 os_prio=0 tid=0x000000001fdba800 nid=0x4f88 waiting for monitor entry [0x0000000020
e1f000]
   java.lang.Thread.State: BLOCKED (on object monitor)
        at com.emaxcard.jvm.TestDeadlockMain.lambda$main$1(TestDeadlockMain.java:41)
        - waiting to lock <0x000000076bbc06b8> (a java.util.concurrent.ConcurrentHashMap)
        - locked <0x000000076bbc06f8> (a java.lang.Object)
        at com.emaxcard.jvm.TestDeadlockMain$$Lambda$2/654845766.run(Unknown Source)
        at java.lang.Thread.run(Thread.java:745)

\"Thread-0\" #12 prio=5 os_prio=0 tid=0x000000001fcf8000 nid=0x6ecc waiting for monitor entry [0x0000000020
d1e000]
   java.lang.Thread.State: BLOCKED (on object monitor)
        at com.emaxcard.jvm.TestDeadlockMain.lambda$main$0(TestDeadlockMain.java:33)
        - waiting to lock <0x000000076bbc06f8> (a java.lang.Object)
        - locked <0x000000076bbc06b8> (a java.util.concurrent.ConcurrentHashMap)
        at com.emaxcard.jvm.TestDeadlockMain$$Lambda$1/2101842856.run(Unknown Source)
        at java.lang.Thread.run(Thread.java:745)

\"Service Thread\" #11 daemon prio=9 os_prio=0 tid=0x000000001f53d800 nid=0x72d0 runnable [0x00000000000000
00]
   java.lang.Thread.State: RUNNABLE

\"C1 CompilerThread3\" #10 daemon prio=9 os_prio=2 tid=0x000000001f4ea800 nid=0x948 waiting on condition [0
x0000000000000000]
   java.lang.Thread.State: RUNNABLE

\"C2 CompilerThread2\" #9 daemon prio=9 os_prio=2 tid=0x000000001f4e8000 nid=0x5ed0 waiting on condition [0
x0000000000000000]
   java.lang.Thread.State: RUNNABLE

\"C2 CompilerThread1\" #8 daemon prio=9 os_prio=2 tid=0x000000001f4e3000 nid=0x6130 waiting on condition [0
x0000000000000000]
   java.lang.Thread.State: RUNNABLE

\"C2 CompilerThread0\" #7 daemon prio=9 os_prio=2 tid=0x000000001f4e0800 nid=0x6804 waiting on condition [0
x0000000000000000]
   java.lang.Thread.State: RUNNABLE

\"Monitor Ctrl-Break\" #6 daemon prio=5 os_prio=0 tid=0x000000001f4a8000 nid=0x52bc runnable [0x000000001f6
4e000]
   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:170)
        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 <0x000000076bce5ac8> (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 <0x000000076bce5ac8> (a java.io.InputStreamReader)
        at java.io.BufferedReader.readLine(BufferedReader.java:389)
        at com.intellij.rt.execution.application.AppMainV2$1.run(AppMainV2.java:61)

\"Attach Listener\" #5 daemon prio=5 os_prio=2 tid=0x000000001e7d2000 nid=0x6478 waiting on condition [0x00
00000000000000]
   java.lang.Thread.State: RUNNABLE

\"Signal Dispatcher\" #4 daemon prio=9 os_prio=2 tid=0x000000001e7d1800 nid=0x5e4c runnable [0x000000000000
0000]
   java.lang.Thread.State: RUNNABLE

\"Finalizer\" #3 daemon prio=8 os_prio=1 tid=0x000000001c774800 nid=0x5df0 in Object.wait() [0x000000001e73
e000]
   java.lang.Thread.State: WAITING (on object monitor)
        at java.lang.Object.wait(Native Method)
        - waiting on <0x000000076b306f58> (a java.lang.ref.ReferenceQueue$Lock)
        at java.lang.ref.ReferenceQueue.remove(ReferenceQueue.java:143)
        - locked <0x000000076b306f58> (a java.lang.ref.ReferenceQueue$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=0x000000001c76e000 nid=0x6828 in Object.wait() [0x000
000001e63f000]
   java.lang.Thread.State: WAITING (on object monitor)
        at java.lang.Object.wait(Native Method)
        - waiting on <0x000000076b306998> (a java.lang.ref.Reference$Lock)
        at java.lang.Object.wait(Object.java:502)
        at java.lang.ref.Reference$ReferenceHandler.run(Reference.java:157)
        - locked <0x000000076b306998> (a java.lang.ref.Reference$Lock)

\"VM Thread\" os_prio=2 tid=0x000000001c76a000 nid=0x3384 runnable

\"GC task thread#0 (ParallelGC)\" os_prio=0 tid=0x0000000002a72000 nid=0x6d44 runnable

\"GC task thread#1 (ParallelGC)\" os_prio=0 tid=0x0000000002a73800 nid=0x61c8 runnable

\"GC task thread#2 (ParallelGC)\" os_prio=0 tid=0x0000000002a75000 nid=0x6a00 runnable

\"GC task thread#3 (ParallelGC)\" os_prio=0 tid=0x0000000002a77800 nid=0x5e6c runnable

\"GC task thread#4 (ParallelGC)\" os_prio=0 tid=0x0000000002a7a000 nid=0x480c runnable

\"GC task thread#5 (ParallelGC)\" os_prio=0 tid=0x0000000002a7b000 nid=0x497c runnable

\"GC task thread#6 (ParallelGC)\" os_prio=0 tid=0x0000000002a7e000 nid=0x13f8 runnable

\"GC task thread#7 (ParallelGC)\" os_prio=0 tid=0x0000000002a7f800 nid=0x40b4 runnable

\"VM Periodic Task Thread\" os_prio=2 tid=0x000000001f53e800 nid=0x7314 waiting on condition

JNI global references: 330


Found one Java-level deadlock:
=============================
\"Thread-1\":
  waiting to lock monitor 0x000000001c773158 (object 0x000000076bbc06b8, a java.util.concurrent.Concurren
tHashMap),
  which is held by \"Thread-0\"
\"Thread-0\":
  waiting to lock monitor 0x000000001c774548 (object 0x000000076bbc06f8, a java.lang.Object),
  which is held by \"Thread-1\"

Java stack information for the threads listed above:
===================================================
\"Thread-1\":
        at com.emaxcard.jvm.TestDeadlockMain.lambda$main$1(TestDeadlockMain.java:41)
        - waiting to lock <0x000000076bbc06b8> (a java.util.concurrent.ConcurrentHashMap)
        - locked <0x000000076bbc06f8> (a java.lang.Object)
        at com.emaxcard.jvm.TestDeadlockMain$$Lambda$2/654845766.run(Unknown Source)
        at java.lang.Thread.run(Thread.java:745)
\"Thread-0\":
        at com.emaxcard.jvm.TestDeadlockMain.lambda$main$0(TestDeadlockMain.java:33)
        - waiting to lock <0x000000076bbc06f8> (a java.lang.Object)
        - locked <0x000000076bbc06b8> (a java.util.concurrent.ConcurrentHashMap)
        at com.emaxcard.jvm.TestDeadlockMain$$Lambda$1/2101842856.run(Unknown Source)
        at java.lang.Thread.run(Thread.java:745)

Found 1 deadlock.

jstack简介

jstack命令用于打印指定Java进程、核心文件或远程调试服务器的Java线程的Java堆栈跟踪信息^[1]。
jstack命令可以生成JVM当前时刻的线程快照。线程快照是当前JVM内每一条线程正在执行的方法堆栈的集合，生成线程快照的主要目的是定位线程出现长时间停顿的原因，如线程间死锁、死循环、请求外部资源导致的长时间等待等。
如果java程序崩溃生成core文件，jstack工具可以用来获得core文件的java stack和native stack的信息，从而可以轻松地知道java程序是如何崩溃和在程序何处发生问题。
当指定的进程在64位Java虚拟机上运行时，可能需要指定-J-d64选项，例如:jstack -J-d64 -m pid。
该命令可能在未来的版本中不可用！！！

语法

jstack [ options ] pid

当看到一些不好的代码时，会发现我还算优秀；当看到优秀的代码时，也才意识到持续学习的重要！--buguge
本文来自博客园，转载请注明原文链接：https://www.cnblogs.com/buguge/p/16622318.html

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来源：https://www.cnblogs.com/buguge/p/16622318.html
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java死锁（Java-level deadlock）

java-level deadlock

deadlock demo及deadlock信息

jstack简介

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