jdk命令行工具系列
(1) - jps:虚拟机进程状态工具
(2) - jinfo:jvm配置信息工具
(3) - jmap:java内存映射工具
(4) - jstack：java堆栈跟踪工具
jdk可视化工具系列
（1）- JConsole：Java监视与管理控制台
（2）- jvisualvm：多合一故障处理工具
测试代码：
package com.jvm.visualvm;
public class Demo4 {
public static void main(String[] args) {
User u1 = new User("u1");
User u2 = new User("u2");
Thread thread1 = new Thread(new SynAddRunalbe(u1, u2, 1, 2, true));
thread1.setName("thread1");
thread1.start();
Thread thread2 = new Thread(new SynAddRunalbe(u1, u2, 2, 1, false));
thread2.setName("thread2");
thread2.start();
}
/**
* 线程死锁等待演示
*/
public static class SynAddRunalbe implements Runnable {
User u1, u2;
int a, b;
boolean flag;
public SynAddRunalbe(User u1, User u2, int a, int b, boolean flag) {
this.u1 = u1;
this.u2 = u2;
this.a = a;
this.b = b;
this.flag = flag;
}
@Override
public void run() {
try {
if (flag) {
synchronized (u1) {
Thread.sleep(100);
synchronized (u2) {
System.out.println(a + b);
}
}
} else {
synchronized (u2) {
Thread.sleep(100);
synchronized (u1) {
System.out.println(a + b);
}
}
}
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}
public static class User {
private String name;
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public User(String name) {
this.name = name;
}
@Override
public String toString() {
return "User{" +
"name='" + name + '\'' +
'}';
}
}
}
问题排查
步骤一：jps查看java进程
>jps -l
5824 com.jvm.visualvm.Demo4
步骤二：使用jstack查看线程堆栈信息
>jstack 5824
2019-06-04 15:34:37
Full thread dump Java HotSpot(TM) 64-Bit Server VM (25.121-b13 mixed mode):
"DestroyJavaVM" #14 prio=5 os_prio=0 tid=0x0000000002cf4000 nid=0x9fd8 waiting on condition [0x0000000000000000]
java.lang.Thread.State: RUNNABLE
"thread2" #13 prio=5 os_prio=0 tid=0x000000002884d800 nid=0x40c4 waiting for monitor entry [0x00000000292ce000]
java.lang.Thread.State: BLOCKED (on object monitor)
at com.jvm.visualvm.Demo4$SynAddRunalbe.run(Demo4.java:49)
- waiting to lock <0x00000007173d4178> (a com.jvm.visualvm.Demo4$User)
- locked <0x00000007173d41b8> (a com.jvm.visualvm.Demo4$User)
at java.lang.Thread.run(Thread.java:745)
"thread1" #12 prio=5 os_prio=0 tid=0x000000002885b800 nid=0x99c0 waiting for monitor entry [0x00000000291cf000]
java.lang.Thread.State: BLOCKED (on object monitor)
at com.jvm.visualvm.Demo4$SynAddRunalbe.run(Demo4.java:42)
- waiting to lock <0x00000007173d41b8> (a com.jvm.visualvm.Demo4$User)
- locked <0x00000007173d4178> (a com.jvm.visualvm.Demo4$User)
at java.lang.Thread.run(Thread.java:745)
"Service Thread" #11 daemon prio=9 os_prio=0 tid=0x0000000027dd9000 nid=0x7f80 runnable [0x0000000000000000]
java.lang.Thread.State: RUNNABLE
"C1 CompilerThread3" #10 daemon prio=9 os_prio=2 tid=0x0000000027d80800 nid=0x3b94 waiting on condition [0x0000000000000000]
java.lang.Thread.State: RUNNABLE
"C2 CompilerThread2" #9 daemon prio=9 os_prio=2 tid=0x0000000027d7c000 nid=0x4c7c waiting on condition [0x0000000000000000]
java.lang.Thread.State: RUNNABLE
"C2 CompilerThread1" #8 daemon prio=9 os_prio=2 tid=0x0000000027d7b000 nid=0x8f4c waiting on condition [0x0000000000000000]
java.lang.Thread.State: RUNNABLE
"C2 CompilerThread0" #7 daemon prio=9 os_prio=2 tid=0x0000000027d73000 nid=0x9094 waiting on condition [0x0000000000000000]
java.lang.Thread.State: RUNNABLE
"Monitor Ctrl-Break" #6 daemon prio=5 os_prio=0 tid=0x0000000027d0a800 nid=0x647c runnable [0x00000000282ce000]
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 <0x0000000717449cd8> (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 <0x0000000717449cd8> (a java.io.InputStreamReader)
at java.io.BufferedReader.readLine(BufferedReader.java:389)
at com.intellij.rt.execution.application.AppMainV2$1.run(AppMainV2.java:64)
"Attach Listener" #5 daemon prio=5 os_prio=2 tid=0x0000000027b61000 nid=0x7cf8 waiting on condition [0x0000000000000000]
java.lang.Thread.State: RUNNABLE
"Signal Dispatcher" #4 daemon prio=9 os_prio=2 tid=0x0000000027b5f800 nid=0x94f4 runnable [0x0000000000000000]
java.lang.Thread.State: RUNNABLE
"Finalizer" #3 daemon prio=8 os_prio=1 tid=0x0000000027af1800 nid=0x9960 in Object.wait() [0x0000000027fce000]
java.lang.Thread.State: WAITING (on object monitor)
at java.lang.Object.wait(Native Method)
- waiting on <0x0000000717188ec8> (a java.lang.ref.ReferenceQueue$Lock)
at java.lang.ref.ReferenceQueue.remove(ReferenceQueue.java:143)
- locked <0x0000000717188ec8> (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=0x0000000002deb000 nid=0xb2bc in Object.wait() [0x0000000027acf000]
java.lang.Thread.State: WAITING (on object monitor)
at java.lang.Object.wait(Native Method)
- waiting on <0x0000000717186b68> (a java.lang.ref.Reference$Lock)
at java.lang.Object.wait(Object.java:502)
at java.lang.ref.Reference.tryHandlePending(Reference.java:191)
- locked <0x0000000717186b68> (a java.lang.ref.Reference$Lock)
at java.lang.ref.Reference$ReferenceHandler.run(Reference.java:153)
"VM Thread" os_prio=2 tid=0x0000000025be9000 nid=0xaa90 runnable
"GC task thread#0 (ParallelGC)" os_prio=0 tid=0x0000000002d0a000 nid=0x3fc0 runnable
"GC task thread#1 (ParallelGC)" os_prio=0 tid=0x0000000002d0b800 nid=0x9cf8 runnable
"GC task thread#2 (ParallelGC)" os_prio=0 tid=0x0000000002d0d000 nid=0x51c runnable
"GC task thread#3 (ParallelGC)" os_prio=0 tid=0x0000000002d0e800 nid=0x24d0 runnable
"GC task thread#4 (ParallelGC)" os_prio=0 tid=0x0000000002d12000 nid=0x618c runnable
"GC task thread#5 (ParallelGC)" os_prio=0 tid=0x0000000002d13000 nid=0x5550 runnable
"GC task thread#6 (ParallelGC)" os_prio=0 tid=0x0000000002d16000 nid=0x8994 runnable
"GC task thread#7 (ParallelGC)" os_prio=0 tid=0x0000000002d17800 nid=0x39cc runnable
"VM Periodic Task Thread" os_prio=2 tid=0x0000000027dd9800 nid=0x5294 waiting on condition
JNI global references: 33
Found one Java-level deadlock:
=============================
"thread2":
waiting to lock monitor 0x0000000028846468 (object 0x00000007173d4178, a com.jvm.visualvm.Demo4$User),
which is held by "thread1"
"thread1":
waiting to lock monitor 0x0000000025bf0bb8 (object 0x00000007173d41b8, a com.jvm.visualvm.Demo4$User),
which is held by "thread2"
Java stack information for the threads listed above:
===================================================
"thread2":
at com.jvm.visualvm.Demo4$SynAddRunalbe.run(Demo4.java:49)
- waiting to lock <0x00000007173d4178> (a com.jvm.visualvm.Demo4$User)
- locked <0x00000007173d41b8> (a com.jvm.visualvm.Demo4$User)
at java.lang.Thread.run(Thread.java:745)
"thread1":
at com.jvm.visualvm.Demo4$SynAddRunalbe.run(Demo4.java:42)
- waiting to lock <0x00000007173d41b8> (a com.jvm.visualvm.Demo4$User)
- locked <0x00000007173d4178> (a com.jvm.visualvm.Demo4$User)
at java.lang.Thread.run(Thread.java:745)
Found 1 deadlock.
可以看出死锁的代码是在Demo4.java的49行和42行，此时我们就可以去优化代码，解决死锁问题。
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