深入分析JVM中线程的创建和运行原理 || JIT(future)

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

-=============================-

 

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
    本文转自网络文章,转载此文章仅为分享知识,如有侵权,请联系博主进行删除。
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