深入分析JVM中线程的创建和运行原理｜｜ JIT（future）

2023年7月17日 396次阅读来源: JVM

https://blog.csdn.net/J080624/article/details/86020746

在JVM中除了应用线程，还有其他的一些线程用于支持JVM的运行，这些线程可以被划分为以下几类：

VM Thread：负责JVM在安全点内的各种操作，这些操作（诸如自动内存管理、取消偏向锁、线程dump、线程挂起等等）在执行过程中需要JVM处于这样一个状态——堆的内容不会被改变，这种状态在JVM里叫做安全点（safe-point）。
Periodic task thread：这个线程负责响应定时触发的事件（例如：中断），用来执行一些定时操作。
GC thread：这些线程负责JVM里的垃圾收集活动；
Compiler threads：这些线程负责在运行时将字节码编译为本地代码；
Singal dispatcher thread：这些线程负责响应外部发给当前JVM进程的信号，并通过调用JVM内的其他线程。

我们再用jstack命令做一次线程dump，就可以得到如下内容：

jstack内容一般在最后：

"Service Thread" #8 daemon prio=9 os_prio=0 tid=0x00007f486018f800 nid=0x3110 runnable [0x0000000000000000]
   java.lang.Thread.State: RUNNABLE

"C1 CompilerThread2" #7 daemon prio=9 os_prio=0 tid=0x00007f4860184800 nid=0x310f waiting on condition [0x0000000000000000]
   java.lang.Thread.State: RUNNABLE

"C2 CompilerThread1" #6 daemon prio=9 os_prio=0 tid=0x00007f4860182800 nid=0x310e waiting on condition [0x0000000000000000]
   java.lang.Thread.State: RUNNABLE

"C2 CompilerThread0" #5 daemon prio=9 os_prio=0 tid=0x00007f486017f800 nid=0x310d waiting on condition [0x0000000000000000]
   java.lang.Thread.State: RUNNABLE

"Signal Dispatcher" #4 daemon prio=9 os_prio=0 tid=0x00007f486017e000 nid=0x310c runnable [0x0000000000000000]
   java.lang.Thread.State: RUNNABLE

"Finalizer" #3 daemon prio=8 os_prio=0 tid=0x00007f486014b000 nid=0x310b in Object.wait() [0x00007f4850bfa000]
   java.lang.Thread.State: WAITING (on object monitor)
	at java.lang.Object.wait(Native Method)
	at java.lang.ref.ReferenceQueue.remove(ReferenceQueue.java:143)
	- locked <0x00000000e0e0c390> (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=0 tid=0x00007f4860146800 nid=0x310a in Object.wait() [0x00007f4850cfb000]
   java.lang.Thread.State: WAITING (on object monitor)
	at java.lang.Object.wait(Native Method)
	at java.lang.Object.wait(Object.java:502)
	at java.lang.ref.Reference.tryHandlePending(Reference.java:191)
	- locked <0x00000000e0e0c5c0> (a java.lang.ref.Reference$Lock)
	at java.lang.ref.Reference$ReferenceHandler.run(Reference.java:153)

"VM Thread" os_prio=0 tid=0x00007f486013f000 nid=0x3109 runnable 

"GC task thread#0 (ParallelGC)" os_prio=0 tid=0x00007f486001e800 nid=0x3105 runnable 

"GC task thread#1 (ParallelGC)" os_prio=0 tid=0x00007f4860020800 nid=0x3106 runnable 

"GC task thread#2 (ParallelGC)" os_prio=0 tid=0x00007f4860022800 nid=0x3107 runnable 

"GC task thread#3 (ParallelGC)" os_prio=0 tid=0x00007f4860024000 nid=0x3108 runnable 

"VM Periodic Task Thread" os_prio=0 tid=0x00007f4860194800 nid=0x3111 waiting on condition 

JNI global references: 1925

可以看到，有2个c2 compiler thread，jdk默认即是2个线程

C2 CompilerThread线程项目启动初期cpu使用率那么高，它在干什么呢？

Java程序在启动的时候所有代码的执行都处于解释执行模式，只有在运行了一段时间后，根据代码方法执行的次数，或代码里循环的执行次数等达到一定的阈值才会编译成机器码，编译成机器码后执行效率会得到大幅提升，而随着执行时间进一步拉长，JVM的各种更高级的编译优化手段就会逐渐加上，例如if条件的执行状况，逃逸分析等。这里的C2 CompilerThread线程干的就是编译优化的活。

编译方式有三种：1）Client模式；2）Server模式；3）Tiered模式。我们服务默认是Server模式。

Server模式是采用c2高级编译的，会比较耗时且要运行一段时间才会触发编译。 Server模式的优点是编译后程序效率较高；

Client模式比较轻量也比较快触发（比Server模式触发快），编译优化后程序效率不如Server模式；

Tiered模式是Client模式和Server模式的折中，一开始会启用Client模式，可以在启动后更快的让部分代码先进入编译优化阶段，之后会启动Server模式，达到程序效率最大优化的目的。

Oracle JDK 7里的HotSpot VM已经开始有比较好的Tiered编译（tiered compilation）支持，可以设置参数-XX:+TieredCompilation来启动Tiered模式，java 8默认就是Tiered模式。

详见：https://www.cnblogs.com/silyvin/p/10226774.html

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HotSpot中内置了两个即时编译器，分别称为 Client Compiler和 Server Compiler ，或者简称为 C1 编译器和 C2 编译器。目前的 HotSpot 编译器默认的是解释器和其中一个即时编译器配合的方式工作，具体是哪一个编译器，取决于虚拟机运行的模式，HotSpot 虚拟机会根据自身版本与计算机的硬件性能自动选择运行模式，用户也可以使用 -client 和 -server 参数强制指定虚拟机运行在 Client 模式或者 Server 模式。这种配合使用的方式称为“混合模式”（Mixed Mode）

被多次调用的方法
被多次执行的循环体

http://www.cnblogs.com/linghu-java/p/8589843.html

附：

Full thread dump Java HotSpot(TM) 64-Bit Server VM (25.151-b12 mixed mode):


"RMI TCP Connection(5)-192.168.0.139" #17 daemon prio=9 os_prio=31 tid=0x00007fba7c830800 nid=0x5c03 runnable [0x000070000f740000]

   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 java.io.BufferedInputStream.fill(BufferedInputStream.java:246)

    at java.io.BufferedInputStream.read(BufferedInputStream.java:265)

    - locked <0x000000076f590708> (a java.io.BufferedInputStream)

    at java.io.FilterInputStream.read(FilterInputStream.java:83)

    at sun.rmi.transport.tcp.TCPTransport.handleMessages(TCPTransport.java:550)

    at sun.rmi.transport.tcp.TCPTransport$ConnectionHandler.run0(TCPTransport.java:826)

    at sun.rmi.transport.tcp.TCPTransport$ConnectionHandler.lambda$run$0(TCPTransport.java:683)

    at sun.rmi.transport.tcp.TCPTransport$ConnectionHandler$$Lambda$3/745402377.run(Unknown Source)

    at java.security.AccessController.doPrivileged(Native Method)

    at sun.rmi.transport.tcp.TCPTransport$ConnectionHandler.run(TCPTransport.java:682)

    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)

    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)

    at java.lang.Thread.run(Thread.java:748)


"RMI TCP Connection(2)-192.168.0.139" #16 daemon prio=9 os_prio=31 tid=0x00007fba7e0b0000 nid=0xa403 in Object.wait() [0x000070000f63c000]

   java.lang.Thread.State: TIMED_WAITING (on object monitor)

    at java.lang.Object.wait(Native Method)

    - waiting on <0x000000076f580878> (a com.sun.jmx.remote.internal.ArrayNotificationBuffer)

    at com.sun.jmx.remote.internal.ArrayNotificationBuffer.fetchNotifications(ArrayNotificationBuffer.java:449)

    - locked <0x000000076f580878> (a com.sun.jmx.remote.internal.ArrayNotificationBuffer)

    at com.sun.jmx.remote.internal.ArrayNotificationBuffer$ShareBuffer.fetchNotifications(ArrayNotificationBuffer.java:227)

    at com.sun.jmx.remote.internal.ServerNotifForwarder.fetchNotifs(ServerNotifForwarder.java:274)

    at javax.management.remote.rmi.RMIConnectionImpl$4.run(RMIConnectionImpl.java:1270)

    at javax.management.remote.rmi.RMIConnectionImpl$4.run(RMIConnectionImpl.java:1268)

    at javax.management.remote.rmi.RMIConnectionImpl.fetchNotifications(RMIConnectionImpl.java:1274)

    at sun.reflect.GeneratedMethodAccessor62.invoke(Unknown Source)

    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)

    at java.lang.reflect.Method.invoke(Method.java:498)

    at sun.rmi.server.UnicastServerRef.dispatch(UnicastServerRef.java:357)

    at sun.rmi.transport.Transport$1.run(Transport.java:200)

    at sun.rmi.transport.Transport$1.run(Transport.java:197)

    at java.security.AccessController.doPrivileged(Native Method)

    at sun.rmi.transport.Transport.serviceCall(Transport.java:196)

    at sun.rmi.transport.tcp.TCPTransport.handleMessages(TCPTransport.java:568)

    at sun.rmi.transport.tcp.TCPTransport$ConnectionHandler.run0(TCPTransport.java:826)

    at sun.rmi.transport.tcp.TCPTransport$ConnectionHandler.lambda$run$0(TCPTransport.java:683)

    at sun.rmi.transport.tcp.TCPTransport$ConnectionHandler$$Lambda$3/745402377.run(Unknown Source)

    at java.security.AccessController.doPrivileged(Native Method)

    at sun.rmi.transport.tcp.TCPTransport$ConnectionHandler.run(TCPTransport.java:682)

    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)

    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)

    at java.lang.Thread.run(Thread.java:748)


"JMX server connection timeout 15" #15 daemon prio=9 os_prio=31 tid=0x00007fba80014800 nid=0xa503 in Object.wait() [0x000070000f53b000]

   java.lang.Thread.State: TIMED_WAITING (on object monitor)

    at java.lang.Object.wait(Native Method)

    - waiting on <0x000000076f5887f8> (a [I)

    at com.sun.jmx.remote.internal.ServerCommunicatorAdmin$Timeout.run(ServerCommunicatorAdmin.java:168)

    - locked <0x000000076f5887f8> (a [I)

    at java.lang.Thread.run(Thread.java:748)


"RMI Scheduler(0)" #14 daemon prio=9 os_prio=31 tid=0x00007fba7c805800 nid=0xa603 waiting on condition [0x000070000f438000]

   java.lang.Thread.State: TIMED_WAITING (parking)

    at sun.misc.Unsafe.park(Native Method)

    - parking to wait for  <0x000000076f598188> (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)


"RMI TCP Accept-0" #12 daemon prio=9 os_prio=31 tid=0x00007fba7d906000 nid=0xa803 runnable [0x000070000f232000]

   java.lang.Thread.State: RUNNABLE

    at java.net.PlainSocketImpl.socketAccept(Native Method)

    at java.net.AbstractPlainSocketImpl.accept(AbstractPlainSocketImpl.java:409)

    at java.net.ServerSocket.implAccept(ServerSocket.java:545)

    at java.net.ServerSocket.accept(ServerSocket.java:513)

    at sun.management.jmxremote.LocalRMIServerSocketFactory$1.accept(LocalRMIServerSocketFactory.java:52)

    at sun.rmi.transport.tcp.TCPTransport$AcceptLoop.executeAcceptLoop(TCPTransport.java:400)

    at sun.rmi.transport.tcp.TCPTransport$AcceptLoop.run(TCPTransport.java:372)

    at java.lang.Thread.run(Thread.java:748)


"Attach Listener" #10 daemon prio=9 os_prio=31 tid=0x00007fba7d865800 nid=0xa903 waiting on condition [0x0000000000000000]

   java.lang.Thread.State: RUNNABLE


"Service Thread" #9 daemon prio=9 os_prio=31 tid=0x00007fba7d803000 nid=0x3903 runnable [0x0000000000000000]

   java.lang.Thread.State: RUNNABLE


"C1 CompilerThread3" #8 daemon prio=9 os_prio=31 tid=0x00007fba7e002000 nid=0x3803 waiting on condition [0x0000000000000000]

   java.lang.Thread.State: RUNNABLE


"C2 CompilerThread2" #7 daemon prio=9 os_prio=31 tid=0x00007fba80000000 nid=0x3703 waiting on condition [0x0000000000000000]

   java.lang.Thread.State: RUNNABLE


"C2 CompilerThread1" #6 daemon prio=9 os_prio=31 tid=0x00007fba7d82d800 nid=0x3e03 waiting on condition [0x0000000000000000]

   java.lang.Thread.State: RUNNABLE


"C2 CompilerThread0" #5 daemon prio=9 os_prio=31 tid=0x00007fba7c020000 nid=0x3f03 waiting on condition [0x0000000000000000]

   java.lang.Thread.State: RUNNABLE


"Signal Dispatcher" #4 daemon prio=9 os_prio=31 tid=0x00007fba7c01e800 nid=0x3403 runnable [0x0000000000000000]

   java.lang.Thread.State: RUNNABLE


"Finalizer" #3 daemon prio=8 os_prio=31 tid=0x00007fba7f022000 nid=0x4903 in Object.wait() [0x000070000e917000]

   java.lang.Thread.State: WAITING (on object monitor)

    at java.lang.Object.wait(Native Method)

    - waiting on <0x000000076f5a0600> (a java.lang.ref.ReferenceQueue$Lock)

    at java.lang.ref.ReferenceQueue.remove(ReferenceQueue.java:143)

    - locked <0x000000076f5a0600> (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=31 tid=0x00007fba7c01d800 nid=0x4b03 in Object.wait() [0x000070000e814000]

   java.lang.Thread.State: WAITING (on object monitor)

    at java.lang.Object.wait(Native Method)

    - waiting on <0x000000076f5983e8> (a java.lang.ref.Reference$Lock)

    at java.lang.Object.wait(Object.java:502)

    at java.lang.ref.Reference.tryHandlePending(Reference.java:191)

    - locked <0x000000076f5983e8> (a java.lang.ref.Reference$Lock)

    at java.lang.ref.Reference$ReferenceHandler.run(Reference.java:153)


"main" #1 prio=5 os_prio=31 tid=0x00007fba7f000000 nid=0x2303 runnable [0x000070000ddf6000]

   java.lang.Thread.State: RUNNABLE

    at GcExample.main(GcExample.java:9)


"VM Thread" os_prio=31 tid=0x00007fba7c01b000 nid=0x2f03 runnable 


"GC task thread#0 (ParallelGC)" os_prio=31 tid=0x00007fba7c007000 nid=0x2007 runnable 


"GC task thread#1 (ParallelGC)" os_prio=31 tid=0x00007fba7d804800 nid=0x2a03 runnable 


"GC task thread#2 (ParallelGC)" os_prio=31 tid=0x00007fba7c007800 nid=0x5303 runnable 


"GC task thread#3 (ParallelGC)" os_prio=31 tid=0x00007fba7f800000 nid=0x2c03 runnable 


"GC task thread#4 (ParallelGC)" os_prio=31 tid=0x00007fba7d805000 nid=0x5103 runnable 


"GC task thread#5 (ParallelGC)" os_prio=31 tid=0x00007fba7c013800 nid=0x5003 runnable 


"GC task thread#6 (ParallelGC)" os_prio=31 tid=0x00007fba7f001000 nid=0x4e03 runnable 


"GC task thread#7 (ParallelGC)" os_prio=31 tid=0x00007fba7c014000 nid=0x4c03 runnable 


"VM Periodic Task Thread" os_prio=31 tid=0x00007fba7d858800 nid=0x3a03 waiting on condition 


JNI global references: 295

OK，从上面这个dump文件中，可以找到Periodic Task Thread、GC Thread、VM Thread、Compiler Thread的身影了。

    原文作者：JVM
    原文地址: https://www.cnblogs.com/silyvin/p/10228184.html
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