1.背景
面试官问:什么情况下会产生死锁?如何定位?
2.代码
package com.ldp.demo01; import com.common.MyThreadUtil; import lombok.extern.slf4j.Slf4j; /** * @author 姿势帝-博客园 * @address https://www.cnblogs.com/newAndHui/ * @WeChat 851298348 * @create 02/01 6:09 * @description <p> * 监控工具的使用: * https://www.cnblogs.com/newAndHui/p/11105956.html * </p> */ @Slf4j public class Test09DeadLock { /** * 死锁测试与定位 * * @param args */ public static void main(String[] args) { Object lockA = new Object(); Object lockB = new Object(); Thread tA = new Thread(() -> { synchronized (lockA) { log.info("获得锁 lockA"); // 1秒后取获取锁 lockB MyThreadUtil.sleep(1); synchronized (lockB) { log.info("获得锁 lockB"); } } }, "tA"); Thread tB = new Thread(() -> { synchronized (lockB) { log.info("获得锁 lockB"); // 2秒后取获取锁 lockA MyThreadUtil.sleep(2); synchronized (lockA) { log.info("获得锁 lockA"); } } }, "tB"); // 启动线程 tA.start(); tB.start(); } }
3.死锁定位
3.1.控制台命令定位
1. jps 查看进程号
E:\workroom4\thread-demo> jps
117044 Jps
96804 Launcher
106872 Test09DeadLock
111560
2.jstack 进程号 查看明细
E:\workroom4\thread-demo>jstack 106872 2022-02-01 18:16:38 Full thread dump Java HotSpot(TM) 64-Bit Server VM (25.152-b16 mixed mode): "DestroyJavaVM" #13 prio=5 os_prio=0 tid=0x00000000033d3800 nid=0x1a300 waiting on condition [0x0000000000000000] java.lang.Thread.State: RUNNABLE "tB" #12 prio=5 os_prio=0 tid=0x000000000b2a5000 nid=0xf4d8 waiting for monitor entry [0x000000000ba4f000] java.lang.Thread.State: BLOCKED (on object monitor) at com.ldp.demo01.Test09DeadLock.lambda$main$1(Test09DeadLock.java:40) - waiting to lock <0x00000000d6a346e0> (a java.lang.Object) - locked <0x00000000d6a346f0> (a java.lang.Object) at com.ldp.demo01.Test09DeadLock$$Lambda$2/2030562336.run(Unknown Source) at java.lang.Thread.run(Thread.java:748) "tA" #11 prio=5 os_prio=0 tid=0x000000000b2a4000 nid=0x187f0 waiting for monitor entry [0x000000000b14e000] java.lang.Thread.State: BLOCKED (on object monitor) at com.ldp.demo01.Test09DeadLock.lambda$main$0(Test09DeadLock.java:29) - waiting to lock <0x00000000d6a346f0> (a java.lang.Object) - locked <0x00000000d6a346e0> (a java.lang.Object) at com.ldp.demo01.Test09DeadLock$$Lambda$1/984849465.run(Unknown Source) at java.lang.Thread.run(Thread.java:748) "Service Thread" #10 daemon prio=9 os_prio=0 tid=0x000000000a51d800 nid=0x172d4 runnable [0x0000000000000000] java.lang.Thread.State: RUNNABLE "C1 CompilerThread2" #9 daemon prio=9 os_prio=2 tid=0x000000000a447800 nid=0x16874 waiting on condition [0x0000000000000000] java.lang.Thread.State: RUNNABLE "C2 CompilerThread1" #8 daemon prio=9 os_prio=2 tid=0x000000000a43b800 nid=0x1d360 waiting on condition [0x0000000000000000] java.lang.Thread.State: RUNNABLE "C2 CompilerThread0" #7 daemon prio=9 os_prio=2 tid=0x000000000a43a800 nid=0x1a6d4 waiting on condition [0x0000000000000000] java.lang.Thread.State: RUNNABLE "Monitor Ctrl-Break" #6 daemon prio=5 os_prio=0 tid=0x000000000a410800 nid=0x1b3d0 runnable [0x000000000aa9e000] 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 <0x00000000d5f354c0> (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 <0x00000000d5f354c0> (a java.io.InputStreamReader) at java.io.BufferedReader.readLine(BufferedReader.java:389) at com.intellij.rt.execution.application.AppMainV2$1.run(AppMainV2.java:64) "Attach Listener" #5 daemon prio=5 os_prio=2 tid=0x0000000009040000 nid=0x18fe4 waiting on condition [0x0000000000000000] java.lang.Thread.State: RUNNABLE "Signal Dispatcher" #4 daemon prio=9 os_prio=2 tid=0x000000000a3a8800 nid=0x17ff8 runnable [0x0000000000000000] java.lang.Thread.State: RUNNABLE "Finalizer" #3 daemon prio=8 os_prio=1 tid=0x00000000034ce000 nid=0x1ceec in Object.wait() [0x000000000a39f000] java.lang.Thread.State: WAITING (on object monitor) at java.lang.Object.wait(Native Method) - waiting on <0x00000000d5d08ec8> (a java.lang.ref.ReferenceQueue$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=0x00000000034c3000 nid=0x14214 in Object.wait() [0x000000000a29f000] 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$ReferenceHandler.run(Reference.java:153) "VM Thread" os_prio=2 tid=0x0000000008ff7000 nid=0x88e0 runnable "GC task thread#0 (ParallelGC)" os_prio=0 tid=0x00000000033e9000 nid=0x1c0c runnable "GC task thread#1 (ParallelGC)" os_prio=0 tid=0x00000000033ea800 nid=0x162fc runnable "GC task thread#2 (ParallelGC)" os_prio=0 tid=0x00000000033ec000 nid=0x18df4 runnable "GC task thread#3 (ParallelGC)" os_prio=0 tid=0x00000000033ed800 nid=0x8fcc runnable "VM Periodic Task Thread" os_prio=2 tid=0x000000000a54a000 nid=0x1bf58 waiting on condition JNI global references: 327 Found one Java-level deadlock: ============================= "tB": waiting to lock monitor 0x00000000034cb938 (object 0x00000000d6a346e0, a java.lang.Object), which is held by "tA" "tA": waiting to lock monitor 0x00000000034c9af8 (object 0x00000000d6a346f0, a java.lang.Object), which is held by "tB" Java stack information for the threads listed above: =================================================== "tB": at com.ldp.demo01.Test09DeadLock.lambda$main$1(Test09DeadLock.java:40) - waiting to lock <0x00000000d6a346e0> (a java.lang.Object) - locked <0x00000000d6a346f0> (a java.lang.Object) at com.ldp.demo01.Test09DeadLock$$Lambda$2/2030562336.run(Unknown Source) at java.lang.Thread.run(Thread.java:748) "tA": at com.ldp.demo01.Test09DeadLock.lambda$main$0(Test09DeadLock.java:29) - waiting to lock <0x00000000d6a346f0> (a java.lang.Object) - locked <0x00000000d6a346e0> (a java.lang.Object) at com.ldp.demo01.Test09DeadLock$$Lambda$1/984849465.run(Unknown Source) at java.lang.Thread.run(Thread.java:748) Found 1 deadlock.
重点是这里:
Found one Java-level deadlock:
=============================
"tB":
waiting to lock monitor 0x00000000034cb938 (object 0x00000000d6a346e0, a java.lang.Object),
which is held by "tA"
"tA":
waiting to lock monitor 0x00000000034c9af8 (object 0x00000000d6a346f0, a java.lang.Object),
which is held by "tB"
3.2.jconsole工具定位
下一步:
jconsole工具的使用之前我们在将jvm的时候详细讲过,不会使用的可以看这里
https://www.cnblogs.com/newAndHui/p/11105956.html