背景

最近学习 Java 线程相关知识，接触到了
jstack
这个命令，挺有意思的。下面动手试试。

jstack 是什么？

简单来说就是，把 java 当前各个线程相关状态打印出来。

实际使用时，首先借助
jps
命令找到希望观察的 java 进程 ID，然后执行
jstack
+ 查出来的进程 ID 来查看该进程的线程状态。

使用 jstack 查看 Spring Boot 启动时线程

手头正好有一个公司的 Spring Boot 项目，把它启动了，然后执行
jps
命令：

$ jps
1992 **Application // 这个就是 Spring Boot 应用的名称（打了星号）
2792
8488 Jps
12028 RemoteMavenServer36
13164
3676 Launcher

既然知道了 Spring Boot 应用的进程 ID，接下来对该进程执行
jstack
命令：

$ jstack 1992
2021-07-24 14:10:34
Full thread dump OpenJDK 64-Bit Server VM (25.292-b10 mixed mode):
// 输出内容很长，下面分组研究

【2】Druid 数据库连接线程

在打印内容中可以看到，第一部分是两个 Druid 数据库连接线程：

"Druid-ConnectionPool-Destroy-566039179" #88 daemon prio=5 os_prio=0 tid=0x000001f19c6e9000 nid=0x2e74 waiting on condition [0x000000861c6fe000]
   java.lang.Thread.State: TIMED_WAITING (sleeping)
        at java.lang.Thread.sleep(Native Method)
        at com.alibaba.druid.pool.DruidDataSource$DestroyConnectionThread.run(DruidDataSource.java:2540)

"Druid-ConnectionPool-Create-566039179" #87 daemon prio=5 os_prio=0 tid=0x000001f19c6ee000 nid=0x1828 waiting on condition [0x000000861c5ff000]
   java.lang.Thread.State: WAITING (parking)
        at sun.misc.Unsafe.park(Native Method)
        - parking to wait for  <0x000000077a9afe10> (a java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject)
        at java.util.concurrent.locks.LockSupport.park(LockSupport.java:175)
        at java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.await(AbstractQueuedSynchronizer.java:2039)
        at com.alibaba.druid.pool.DruidDataSource$CreateConnectionThread.run(DruidDataSource.java:2443)

【1】MySQL Statement Cancellation Timer 线程

接着是一个相当奇怪的“MySQL 语句取消计时器”：

"MySQL Statement Cancellation Timer" #86 daemon prio=5 os_prio=0 tid=0x000001f19c6e5000 nid=0x778 in Object.wait() [0x000000861c4ff000]
   java.lang.Thread.State: WAITING (on object monitor)
        at java.lang.Object.wait(Native Method)
        - waiting on <0x000000076d266448> (a java.util.TaskQueue)
        at java.lang.Object.wait(Object.java:502)
        at java.util.TimerThread.mainLoop(Timer.java:526)
        - locked <0x000000076d266448> (a java.util.TaskQueue)
        at java.util.TimerThread.run(Timer.java:505)

【6】RMI 相关线程

查了一下，
RMI
是
Java Remote Method Invocation
，相当于 Java 内置的 RPC 吧。

【5】RMI TCP 连接线程

然后是 5 个
RMI TCP
连接线程，中间隔了很远。

但是我不太明白，只是启动一个 Spring Boot，怎么就涉及 RMI 了？

"RMI TCP Connection(7)-172.27.80.1" #83 daemon prio=5 os_prio=0 tid=0x000001f19c6eb800 nid=0x1008 runnable [0x000000861c2fe000]
   java.lang.Thread.State: RUNNABLE
        at java.net.SocketInputStream.socketRead0(Native Method)
 		# 中间略
 		at java.lang.Thread.run(Thread.java:748)

"RMI TCP Connection(6)-172.27.80.1" #80 daemon prio=5 os_prio=0 tid=0x000001f19c6ec800 nid=0x3e38 runnable [0x000000861c1fe000]
   java.lang.Thread.State: RUNNABLE
   		at java.net.SocketInputStream.socketRead0(Native Method)
   		# 中间略
   		at java.lang.Thread.run(Thread.java:748)
   		
   		
# 中间隔了很多很多别的线程


"RMI TCP Connection(5)-172.27.80.1" #30 daemon prio=5 os_prio=0 tid=0x000001f19938a800 nid=0x1df4 runnable [0x0000008619afd000]
   java.lang.Thread.State: RUNNABLE
        at java.net.SocketInputStream.socketRead0(Native Method)
        # 中间略
        at java.lang.Thread.run(Thread.java:748)

"RMI TCP Connection(4)-172.27.80.1" #28 daemon prio=5 os_prio=0 tid=0x000001f1997f1800 nid=0x32dc runnable [0x00000086199fe000]
   java.lang.Thread.State: RUNNABLE
        at java.net.SocketInputStream.socketRead0(Native Method)
        # 中间略
        at java.lang.Thread.run(Thread.java:748)
"RMI TCP Connection(2)-172.27.80.1" #16 daemon prio=5 os_prio=0 tid=0x000001f19a009000 nid=0x11d8 runnable [0x0000008619bfe000]
   java.lang.Thread.State: RUNNABLE
        at java.net.SocketInputStream.socketRead0(Native Method)
        # 中间略
        at java.lang.Thread.run(Thread.java:748)

还有，这里的
172.27.80.1
是谁？

查了一下，是
Ethernet adapter vEthernet (Default Switch)
：

Ethernet adapter vEthernet (Default Switch):

   Connection-specific DNS Suffix  . :
   Link-local IPv6 Address . . . . . : fe80::c97e:8317:192b:14ae%54
   IPv4 Address. . . . . . . . . . . : 172.27.80.1
   Subnet Mask . . . . . . . . . . . : 255.255.240.0
   Default Gateway . . . . . . . . . :

【1】RMI 调度线程

在很靠后的位置有个
RMI
调度线程：

"RMI Scheduler(0)" #17 daemon prio=5 os_prio=0 tid=0x000001f19a014000 nid=0x6f0 waiting on condition [0x0000008619cfe000]
   java.lang.Thread.State: TIMED_WAITING (parking)
        at sun.misc.Unsafe.park(Native Method)
        - parking to wait for  <0x00000006c2939c20> (a java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject)
        # 中间略
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
        at java.lang.Thread.run(Thread.java:748)

【1】RMI 接受线程

最后面有个
RMI
接受线程：

"RMI TCP Accept-0" #13 daemon prio=5 os_prio=0 tid=0x000001f199965800 nid=0x287c runnable [0x00000086197ff000]
   java.lang.Thread.State: RUNNABLE
        at java.net.DualStackPlainSocketImpl.accept0(Native Method)
        at java.net.DualStackPlainSocketImpl.socketAccept(DualStackPlainSocketImpl.java:131)
        at java.net.AbstractPlainSocketImpl.accept(AbstractPlainSocketImpl.java:409)
        at java.net.PlainSocketImpl.accept(PlainSocketImpl.java:199)
        - locked <0x00000006c293a3a8> (a java.net.SocksSocketImpl)
        at java.net.ServerSocket.implAccept(ServerSocket.java:560)
        at java.net.ServerSocket.accept(ServerSocket.java:528)
        at sun.management.jmxremote.LocalRMIServerSocketFactory$1.accept(LocalRMIServerSocketFactory.java:52)
        at sun.rmi.transport.tcp.TCPTransport$AcceptLoop.executeAcceptLoop(TCPTransport.java:405)
        at sun.rmi.transport.tcp.TCPTransport$AcceptLoop.run(TCPTransport.java:377)
        at java.lang.Thread.run(Thread.java:748)

【1】DestroyJavaVM 线程

然后是一个
DestroyJavaVM
线程。

简单来说，这个线程什么都不干，就是等着其他非守护线程的活儿都干完了（
join
），就关闭 Java 虚拟机。

参考链接：

DestroyJavaVM thread ALWAYS running

"DestroyJavaVM" #75 prio=5 os_prio=0 tid=0x000001f19c6e6000 nid=0x3d08 waiting on condition [0x0000000000000000]
   java.lang.Thread.State: RUNNABLE

【14】端口 8080 的 HTTP 相关线程

接下来是 HTTP 相关的三类线程。
8080
端口是负责向用户提供服务的。

参考链接：

Tomcat NIO线程模型深入分析

【1】HTTP NIO Acceptor 线程

Acceptor 线程比较好理解，应该是专门负责接受请求：

"http-nio-8080-Acceptor-0" #73 daemon prio=5 os_prio=0 tid=0x000001f19c6e8800 nid=0x3a28 runnable [0x000000861c0fe000]
   java.lang.Thread.State: RUNNABLE
        at sun.nio.ch.ServerSocketChannelImpl.accept0(Native Method)
        at sun.nio.ch.ServerSocketChannelImpl.accept(ServerSocketChannelImpl.java:421)
        at sun.nio.ch.ServerSocketChannelImpl.accept(ServerSocketChannelImpl.java:249)
        - locked <0x000000077a5c2618> (a java.lang.Object)
        at org.apache.tomcat.util.net.NioEndpoint.serverSocketAccept(NioEndpoint.java:448)
        at org.apache.tomcat.util.net.NioEndpoint.serverSocketAccept(NioEndpoint.java:70)
        at org.apache.tomcat.util.net.Acceptor.run(Acceptor.java:95)
        at java.lang.Thread.run(Thread.java:748)

【2】HTTP NIO ClientPoller 线程

接下来是两个 poller 线程。

简单来说就是负责观察，看前面被 acceptor 线程接受请求后创建的 channel，哪个可读/可写了，就派执行线程去处理。

前一阵刚学到，这叫 IO 多路复用模型，但我总是愿意简单理解为“事件驱动”。简单来说就是，有事儿的时候再干活儿，没事儿的时候歇着。也不是说这种模型多合理，这太正常了，是之前的模型太不合理了，没事儿的时候也要阻塞。

"http-nio-8080-ClientPoller-1" #72 daemon prio=5 os_prio=0 tid=0x000001f19c6e4800 nid=0x1f4c runnable [0x000000861bffe000]
   java.lang.Thread.State: RUNNABLE
        at sun.nio.ch.WindowsSelectorImpl$SubSelector.poll0(Native Method)
        # 中间略
        at java.lang.Thread.run(Thread.java:748)

"http-nio-8080-ClientPoller-0" #71 daemon prio=5 os_prio=0 tid=0x000001f19c4dc800 nid=0x293c runnable [0x000000861befe000]
   java.lang.Thread.State: RUNNABLE
        at sun.nio.ch.WindowsSelectorImpl$SubSelector.poll0(Native Method)
        # 中间略
        at java.lang.Thread.run(Thread.java:748)

【10】HTTP NIO 执行线程

这就是真正干活儿的线程了，一共 10 个，可以理解为一个线程池。

这里省去中间的，放上首尾两个线程：

"http-nio-8080-exec-10" #70 daemon prio=5 os_prio=0 tid=0x000001f19c4db800 nid=0x1140 waiting on condition [0x000000861bdff000]
   java.lang.Thread.State: WAITING (parking)
        at sun.misc.Unsafe.park(Native Method)
        - parking to wait for  <0x000000077a584018> (a java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject)
        at java.util.concurrent.locks.LockSupport.park(LockSupport.java:175)
        at java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.await(AbstractQueuedSynchronizer.java:2039)
        at java.util.concurrent.LinkedBlockingQueue.take(LinkedBlockingQueue.java:442)
        at org.apache.tomcat.util.threads.TaskQueue.take(TaskQueue.java:107)
        at org.apache.tomcat.util.threads.TaskQueue.take(TaskQueue.java:33)
        at java.util.concurrent.ThreadPoolExecutor.getTask(ThreadPoolExecutor.java:1074)
        at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1134)
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
        at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
        at java.lang.Thread.run(Thread.java:748)
        
# 中间略

"http-nio-8080-exec-1" #61 daemon prio=5 os_prio=0 tid=0x000001f19c4d0000 nid=0x10f8 waiting on condition [0x000000861b4ff000]
   java.lang.Thread.State: WAITING (parking)
        at sun.misc.Unsafe.park(Native Method)
        - parking to wait for  <0x000000077a584018> (a java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject)
        at java.util.concurrent.locks.LockSupport.park(LockSupport.java:175)
        at java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.await(AbstractQueuedSynchronizer.java:2039)
        at java.util.concurrent.LinkedBlockingQueue.take(LinkedBlockingQueue.java:442)
        at org.apache.tomcat.util.threads.TaskQueue.take(TaskQueue.java:107)
        at org.apache.tomcat.util.threads.TaskQueue.take(TaskQueue.java:33)
        at java.util.concurrent.ThreadPoolExecutor.getTask(ThreadPoolExecutor.java:1074)
        at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1134)
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
        at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
        at java.lang.Thread.run(Thread.java:748)

【1】BlockPoller 线程

说实话，我没太明白这个跟上面的 ClientPoller 有啥区别：

"NioBlockingSelector.BlockPoller-2" #60 daemon prio=5 os_prio=0 tid=0x000001f19c4d3000 nid=0x219c runnable [0x000000861b3fe000]
   java.lang.Thread.State: RUNNABLE
        at sun.nio.ch.WindowsSelectorImpl$SubSelector.poll0(Native Method)
        at sun.nio.ch.WindowsSelectorImpl$SubSelector.poll(WindowsSelectorImpl.java:314)
        at sun.nio.ch.WindowsSelectorImpl$SubSelector.access$400(WindowsSelectorImpl.java:293)
        at sun.nio.ch.WindowsSelectorImpl.doSelect(WindowsSelectorImpl.java:174)
        at sun.nio.ch.SelectorImpl.lockAndDoSelect(SelectorImpl.java:86)
        - locked <0x000000077a586688> (a sun.nio.ch.Util$3)
        - locked <0x000000077a586678> (a java.util.Collections$UnmodifiableSet)
        - locked <0x000000077a586508> (a sun.nio.ch.WindowsSelectorImpl)
        at sun.nio.ch.SelectorImpl.select(SelectorImpl.java:97)
        at org.apache.tomcat.util.net.NioBlockingSelector$BlockPoller.run(NioBlockingSelector.java:304)

【1】调度线程

调度线程只有一个，这很合理。应该就是它在决定哪些线程获得当前的 CPU 时间了吧！

注意，这是目前第一个“非守护线程”，没有标注
daemon
。

"scheduling-1" #59 prio=5 os_prio=0 tid=0x000001f19c4d7000 nid=0x38b8 waiting on condition [0x000000861b2ff000]
   java.lang.Thread.State: TIMED_WAITING (parking)
        at sun.misc.Unsafe.park(Native Method)
        - parking to wait for  <0x000000077ad451e0> (a java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject)
        at java.util.concurrent.locks.LockSupport.parkNanos(LockSupport.java:215)
        at java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.awaitNanos(AbstractQueuedSynchronizer.java:2078)
        at java.util.concurrent.ScheduledThreadPoolExecutor$DelayedWorkQueue.take(ScheduledThreadPoolExecutor.java:1093)
        at java.util.concurrent.ScheduledThreadPoolExecutor$DelayedWorkQueue.take(ScheduledThreadPoolExecutor.java:809)
        at java.util.concurrent.ThreadPoolExecutor.getTask(ThreadPoolExecutor.java:1074)
        at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1134)
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
        at java.lang.Thread.run(Thread.java:748)

【14】端口8293 的 HTTP 相关线程

这个接口是用来提供内部管理服务的。在
application.yml
中：

management:
  server:
    port: 8293

这 14 个线程和上面
8080
端口的 14 个线程类似，这里就不展开了。

【2】container 线程

接下来是一个
container
线程，然后隔了几个其他线程，又来了另一个
container
线程。

注意，它们也是非守护线程。干什么用的目前还没搞懂，应该是和
tomcat
有关。

"container-1" #43 prio=5 os_prio=0 tid=0x000001f19c3a1800 nid=0x1104 waiting on condition [0x000000861a3ff000]
   java.lang.Thread.State: TIMED_WAITING (sleeping)
        at java.lang.Thread.sleep(Native Method)
        at org.apache.catalina.core.StandardServer.await(StandardServer.java:568)
        at org.springframework.boot.web.embedded.tomcat.TomcatWebServer$1.run(TomcatWebServer.java:181)

# 中间掺杂了其他线程

"container-0" #34 prio=5 os_prio=0 tid=0x000001f19a843800 nid=0x1b20 waiting on condition [0x000000861a0ff000]
   java.lang.Thread.State: TIMED_WAITING (sleeping)
        at java.lang.Thread.sleep(Native Method)
        at org.apache.catalina.core.StandardServer.await(StandardServer.java:568)
        at org.springframework.boot.web.embedded.tomcat.TomcatWebServer$1.run(TomcatWebServer.java:181)

【3】Catalina-utility 线程

然后是 4 个 Catalina-utility 线程。没挨在一起不说，奇怪的是，有两个 1 号、两个 2 号。

这个也不是守护进程，目前还没搞清楚是干嘛的。

"Catalina-utility-2" #42 prio=1 os_prio=-2 tid=0x000001f19c3a5800 nid=0x600 waiting on condition [0x000000861a2fe000]
   java.lang.Thread.State: TIMED_WAITING (parking)
        at sun.misc.Unsafe.park(Native Method)
        - parking to wait for  <0x000000077ac6aef0> (a java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject)
        # 中间略
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
        at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
        at java.lang.Thread.run(Thread.java:748)

"Catalina-utility-1" #41 prio=1 os_prio=-2 tid=0x000001f19c3a0800 nid=0x2bc4 waiting on condition [0x000000861a1ff000]
   java.lang.Thread.State: WAITING (parking)
        at sun.misc.Unsafe.park(Native Method)
        - parking to wait for  <0x000000077ac6aef0> (a java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject)
        # 中间略
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
        at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
        at java.lang.Thread.run(Thread.java:748)

（中间夹杂了别的线程）

"Catalina-utility-2" #33 prio=1 os_prio=-2 tid=0x000001f19a843000 nid=0x367c waiting on condition [0x0000008619fff000]
   java.lang.Thread.State: TIMED_WAITING (parking)
        at sun.misc.Unsafe.park(Native Method)
        - parking to wait for  <0x000000077a5e42c0> (a java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject)
        # 中间略
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
        at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
        at java.lang.Thread.run(Thread.java:748)

"Catalina-utility-1" #32 prio=1 os_prio=-2 tid=0x000001f19a5ce000 nid=0x270c waiting on condition [0x0000008619efe000]
   java.lang.Thread.State: WAITING (parking)
        at sun.misc.Unsafe.park(Native Method)
        - parking to wait for  <0x000000077a5e42c0> (a java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject)
        # 中间略
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
        at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
        at java.lang.Thread.run(Thread.java:748)

【1】Log4j 日志线程

接着看到了熟悉的
Log4j
线程！

之前 Debug 的时候就注意到过，
Log4j
打日志不是同步的，有的时候打印日志的语句过去好几条都没打，然后又一下子打出来好几条。。

原来是用了一个单独的线程，异步来打印日志呀！这下明白了。

这个是守护线程，非常合理，就是来帮忙的嘛：

"Log4j2-TF-6-AsyncLoggerConfig-2" #19 daemon prio=5 os_prio=0 tid=0x000001f19a2a5000 nid=0x26e4 waiting on condition [0x0000008619dff000]
   java.lang.Thread.State: TIMED_WAITING (parking)
        at sun.misc.Unsafe.park(Native Method)
        - parking to wait for  <0x00000006c27729a8> (a java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject)
        at java.util.concurrent.locks.LockSupport.parkNanos(LockSupport.java:215)
        at java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.awaitNanos(AbstractQueuedSynchronizer.java:2078)
        at com.lmax.disruptor.TimeoutBlockingWaitStrategy.waitFor(TimeoutBlockingWaitStrategy.java:38)
        at com.lmax.disruptor.ProcessingSequenceBarrier.waitFor(ProcessingSequenceBarrier.java:56)
        at com.lmax.disruptor.BatchEventProcessor.processEvents(BatchEventProcessor.java:159)
        at com.lmax.disruptor.BatchEventProcessor.run(BatchEventProcessor.java:125)
        at java.lang.Thread.run(Thread.java:748)

【1】Service 线程

暂时没搞明白，总之是个守护线程：

"Service Thread" #11 daemon prio=9 os_prio=0 tid=0x000001f1996e1800 nid=0x270 runnable [0x0000000000000000]
   java.lang.Thread.State: RUNNABLE

【4】编译器线程

看来这就是大名鼎鼎的 JIT 编译器了！编译器线程会在应用运行的过程中，把用到多的部分编译为机器码，以提高性能。

我用的是
corretto-1.8
JRE，编译器线程的数量可能和这个有关系吧：

"C1 CompilerThread3" #10 daemon prio=9 os_prio=2 tid=0x000001f199667800 nid=0xc94 waiting on condition [0x0000000000000000]
   java.lang.Thread.State: RUNNABLE

"C2 CompilerThread2" #9 daemon prio=9 os_prio=2 tid=0x000001f199655800 nid=0x29b8 waiting on condition [0x0000000000000000]
   java.lang.Thread.State: RUNNABLE

"C2 CompilerThread1" #8 daemon prio=9 os_prio=2 tid=0x000001f199655000 nid=0x3c10 waiting on condition [0x0000000000000000]
   java.lang.Thread.State: RUNNABLE

"C2 CompilerThread0" #7 daemon prio=9 os_prio=2 tid=0x000001f199653800 nid=0x1f0c waiting on condition [0x0000000000000000]
   java.lang.Thread.State: RUNNABLE

【1】中断线程

什么。。这也是个线程？？专门用来监听
Ctrl C
吗？。。

"Monitor Ctrl-Break" #6 daemon prio=5 os_prio=0 tid=0x000001f1995d9800 nid=0x21f4 runnable [0x00000086191fe000]
   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 <0x00000006c29705c0> (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 <0x00000006c29705c0> (a java.io.InputStreamReader)
        at java.io.BufferedReader.readLine(BufferedReader.java:389)
        at com.intellij.rt.execution.application.AppMainV2$1.run(AppMainV2.java:48)

【1】Attach 线程

似乎是帮助 Debug 用的一个守护线程：

"Attach Listener" #5 daemon prio=5 os_prio=2 tid=0x000001f1972d8800 nid=0x30d0 waiting on condition [0x0000000000000000]
   java.lang.Thread.State: RUNNABLE

参考链接：

Understanding JVM’s “Attach Listener” thread

【1】信号分派线程

按字面理解，分派信号的一个守护线程：

"Signal Dispatcher" #4 daemon prio=9 os_prio=2 tid=0x000001f197295000 nid=0x41c runnable [0x0000000000000000]
   java.lang.Thread.State: RUNNABLE

【1】Finalizer 线程

这个应该是垃圾回收时，专门用来调用被回收对象的
finalize
方法的守护线程：

"Finalizer" #3 daemon prio=8 os_prio=1 tid=0x000001f197276800 nid=0x12d8 in Object.wait() [0x0000008618eff000]
   java.lang.Thread.State: WAITING (on object monitor)
        at java.lang.Object.wait(Native Method)
        - waiting on <0x00000006c2972a20> (a java.lang.ref.ReferenceQueue$Lock)
        at java.lang.ref.ReferenceQueue.remove(ReferenceQueue.java:144)
        - locked <0x00000006c2972a20> (a java.lang.ref.ReferenceQueue$Lock)
        at java.lang.ref.ReferenceQueue.remove(ReferenceQueue.java:165)
        at java.lang.ref.Finalizer$FinalizerThread.run(Finalizer.java:216)

参考链接：

what will the Finalizer thread do if there is a infinite loop or deadlock in the Java finalize method

【1】Reference Handler 线程

暂时不知道是干嘛的，推测和垃圾回收有关：

"Reference Handler" #2 daemon prio=10 os_prio=2 tid=0x000001f1fc0d5000 nid=0xf08 in Object.wait() [0x0000008618dff000]
   java.lang.Thread.State: WAITING (on object monitor)
        at java.lang.Object.wait(Native Method)
        - waiting on <0x00000006c2985e78> (a java.lang.ref.Reference$Lock)
        at java.lang.Object.wait(Object.java:502)
        at java.lang.ref.Reference.tryHandlePending(Reference.java:191)
        - locked <0x00000006c2985e78> (a java.lang.ref.Reference$Lock)
        at java.lang.ref.Reference$ReferenceHandler.run(Reference.java:153)

【1】VM 线程

似乎也和垃圾回收等操作有很大关系，而且
jstack
命令很可能也是借助这个线程实现的。奇怪的是，这个居然不是守护线程：

"VM Thread" os_prio=2 tid=0x000001f197250000 nid=0x60 runnable

参考链接：

What does java “VM thread” do?

【8】垃圾回收线程

顾名思义，用来进行垃圾回收的线程（居然不是守护线程？？）：

"GC task thread#0 (ParallelGC)" os_prio=0 tid=0x000001f1fc071800 nid=0x29d8 runnable

"GC task thread#1 (ParallelGC)" os_prio=0 tid=0x000001f1fc073000 nid=0x19f0 runnable

"GC task thread#2 (ParallelGC)" os_prio=0 tid=0x000001f1fc074800 nid=0x3f4c runnable

"GC task thread#3 (ParallelGC)" os_prio=0 tid=0x000001f1fc075800 nid=0x39b0 runnable

"GC task thread#4 (ParallelGC)" os_prio=0 tid=0x000001f1fc079000 nid=0x2194 runnable

"GC task thread#5 (ParallelGC)" os_prio=0 tid=0x000001f1fc07a000 nid=0x3bc runnable

"GC task thread#6 (ParallelGC)" os_prio=0 tid=0x000001f1fc07d000 nid=0x8ec runnable

"GC task thread#7 (ParallelGC)" os_prio=0 tid=0x000001f1fc07e000 nid=0x3d20 runnable

【1】VM 定期任务线程

似乎是用来对 JVM 进行采样和性能分析的：

"VM Periodic Task Thread" os_prio=2 tid=0x000001f199969800 nid=0x1044 waiting on condition

参考链接：

What is the “VM Periodic Task Thread”?

JNI global references

在输出的最后，还有这样一行：

JNI global references: 1504

虽然不是一个线程吧。

小结

没想到简单跑一个 Spring Boot 应用，就出来这么多线程！

之后有时间的话可以好好研究一下，分分类，继续更新吧。

原文链接：https://blog.csdn.net/VoisSurTonChemin/article/details/119058738

jstack 命令检查 Spring MVC 应用启动时的各个线程

目录

背景

jstack 是什么？

使用 jstack 查看 Spring Boot 启动时线程

【2】Druid 数据库连接线程

【1】MySQL Statement Cancellation Timer 线程

【6】RMI 相关线程

【5】RMI TCP 连接线程

【1】RMI 调度线程

【1】RMI 接受线程

【1】DestroyJavaVM 线程

【14】端口 8080 的 HTTP 相关线程

【1】HTTP NIO Acceptor 线程

【2】HTTP NIO ClientPoller 线程

【10】HTTP NIO 执行线程

【1】BlockPoller 线程

【1】调度线程

【14】端口8293 的 HTTP 相关线程

【2】container 线程

【3】Catalina-utility 线程

【1】Log4j 日志线程

【1】Service 线程

【4】编译器线程

【1】中断线程

【1】Attach 线程

【1】信号分派线程

【1】Finalizer 线程

【1】Reference Handler 线程

【1】VM 线程

【8】垃圾回收线程

【1】VM 定期任务线程

JNI global references

小结

目录

背景

jstack 是什么？

使用 jstack 查看 Spring Boot 启动时线程

【2】Druid 数据库连接线程

【1】MySQL Statement Cancellation Timer 线程

【6】RMI 相关线程

【5】RMI TCP 连接线程

【1】RMI 调度线程

【1】RMI 接受线程

【1】DestroyJavaVM 线程

【14】端口 8080 的 HTTP 相关线程

【1】HTTP NIO Acceptor 线程

【2】HTTP NIO ClientPoller 线程

【10】HTTP NIO 执行线程

【1】BlockPoller 线程

【1】调度线程

【14】端口8293 的 HTTP 相关线程

【2】container 线程

【3】Catalina-utility 线程

【1】Log4j 日志线程

【1】Service 线程

【4】编译器线程

【1】中断线程

【1】Attach 线程

【1】信号分派线程

【1】Finalizer 线程

【1】Reference Handler 线程

【1】VM 线程

【8】垃圾回收线程

【1】VM 定期任务线程

JNI global references

小结

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