JVM 基础知识

王小明_HIT

发布于 2020-02-17 13:53:19

6290

文章被收录于专栏：程序员奇点程序员奇点

什么 JVM ？

JVM 是可运行 Java 中假想的计算机，就是在真实的计算机上模拟计算机功能，包括一套字节指令，一套寄存器，一个栈，一个垃圾回收，堆，一个存储区域，JVM 是运行在操作系统之上，它与硬件没有直接的交互。

Java 源文件通过编译器，能够生产相应的 .class 文件，也就是字节码文件。而字节码又通过 Java 虚拟机中解释器，编译成特定机器上的机器码。

1. Java 源码文件 -----》编译器 ------》字节码文件

2. 字节码文件 -----》JVM ----》机器码

每种平台的解释器是不同的，但是实现的虚拟机是相同的，这也就是 Java 为什么能够跨平台的原因。当一个程序从开始运行，这是虚拟机开始实例化，多个程序启动就会存在多个虚拟机程序。程序退出或者关闭，虚拟机消亡，多个虚拟机实例之间数据不能共享。

Hotspot JVM 中的 Java 线程与原生操作系统线程有直接的映射关系。当线程本地存储，缓冲区分配，同步对象，栈，程序计数器准备好之后，创建一个操作系统原生线程，Java 线程结束，原生线程将被回收。

Hotspot JVM 后台运行的系统线程主要有下面几个

列表参考

-- ::
Full thread dump Java HotSpot(TM) 64-Bit Server VM (25.40-b25 mixed mode):

"Service Thread" #10 daemon prio= os_prio= tid=0x00000000195ee800 nid=0x1bc runnable [0x0000000000000000]
   java.lang.Thread.State: RUNNABLE

"C1 CompilerThread2" # daemon prio= os_prio= tid=0x00000000195ec000 nid=0x4750 waiting on condition [0x0000000000000000]
   java.lang.Thread.State: RUNNABLE

"C2 CompilerThread1" # daemon prio= os_prio= tid=0x0000000019593000 nid=0x51e0 waiting on condition [0x0000000000000000]
   java.lang.Thread.State: RUNNABLE

"C2 CompilerThread0" # daemon prio= os_prio= tid=0x0000000019590800 nid=0x4704 waiting on condition [0x0000000000000000]
   java.lang.Thread.State: RUNNABLE

"Monitor Ctrl-Break" # daemon prio= os_prio= tid=0x000000001956f000 nid=0x2f7c runnable [0x0000000019e2e000]
   java.lang.Thread.State: RUNNABLE
    at java.net.SocketInputStream.socketRead0(Native Method)
    at java.net.SocketInputStream.socketRead(SocketInputStream.java:)
    at java.net.SocketInputStream.read(SocketInputStream.java:)
    at java.net.SocketInputStream.read(SocketInputStream.java:)
    at sun.nio.cs.StreamDecoder.readBytes(StreamDecoder.java:)
    at sun.nio.cs.StreamDecoder.implRead(StreamDecoder.java:)
    at sun.nio.cs.StreamDecoder.read(StreamDecoder.java:)
    - locked <0x00000000d5fadb60> (a java.io.InputStreamReader)
    at java.io.InputStreamReader.read(InputStreamReader.java:)
    at java.io.BufferedReader.fill(BufferedReader.java:)
    at java.io.BufferedReader.readLine(BufferedReader.java:)
    - locked <0x00000000d5fadb60> (a java.io.InputStreamReader)
    at java.io.BufferedReader.readLine(BufferedReader.java:)
    at com.intellij.rt.execution.application.AppMainV2$.run(AppMainV2.java:)

"Attach Listener" # daemon prio= os_prio= tid=0x0000000017c2b000 nid=0x5050 waiting on condition [0x0000000000000000]
   java.lang.Thread.State: RUNNABLE

"Signal Dispatcher" # daemon prio= os_prio= tid=0x0000000017be0000 nid=0x13b0 runnable [0x0000000000000000]
   java.lang.Thread.State: RUNNABLE

"Finalizer" # daemon prio= os_prio= tid=0x0000000003043000 nid=0x2d9c in Object.wait() [0x0000000018f2f000]
   java.lang.Thread.State: WAITING (on object monitor)
    at java.lang.Object.wait(Native Method)
    - waiting on <0x00000000d5b86f58> (a java.lang.ref.ReferenceQueue$Lock)
    at java.lang.ref.ReferenceQueue.remove(ReferenceQueue.java:)
    - locked <0x00000000d5b86f58> (a java.lang.ref.ReferenceQueue$Lock)
    at java.lang.ref.ReferenceQueue.remove(ReferenceQueue.java:)
    at java.lang.ref.Finalizer$FinalizerThread.run(Finalizer.java:)

"Reference Handler" # daemon prio= os_prio= tid=0x0000000003040000 nid=0x539c in Object.wait() [0x0000000018e2e000]
   java.lang.Thread.State: WAITING (on object monitor)
    at java.lang.Object.wait(Native Method)
    - waiting on <0x00000000d5b86998> (a java.lang.ref.Reference$Lock)
    at java.lang.Object.wait(Object.java:)
    at java.lang.ref.Reference$ReferenceHandler.run(Reference.java:)
    - locked <0x00000000d5b86998> (a java.lang.ref.Reference$Lock)

"main" # prio= os_prio= tid=0x0000000002f53800 nid=0x1ea0 runnable [0x0000000002d5e000]
   java.lang.Thread.State: RUNNABLE
    at java.io.FileInputStream.readBytes(Native Method)
    at java.io.FileInputStream.read(FileInputStream.java:)
    at java.io.BufferedInputStream.read1(BufferedInputStream.java:)
    at java.io.BufferedInputStream.read(BufferedInputStream.java:)
    - locked <0x00000000d5bdc1c8> (a java.io.BufferedInputStream)
    at sun.nio.cs.StreamDecoder.readBytes(StreamDecoder.java:)
    at sun.nio.cs.StreamDecoder.implRead(StreamDecoder.java:)
    at sun.nio.cs.StreamDecoder.read(StreamDecoder.java:)
    - locked <0x00000000d5efa2b8> (a java.io.InputStreamReader)
    at java.io.InputStreamReader.read(InputStreamReader.java:)
    at java.io.Reader.read(Reader.java:)
    at java.util.Scanner.readInput(Scanner.java:)
    at java.util.Scanner.hasNext(Scanner.java:)
    at algorithm.Main.main(Main.java:)

"VM Thread" os_prio= tid=0x0000000017b97800 nid=0x3c78 runnable 

"GC task thread#0 (ParallelGC)" os_prio= tid=0x0000000002f69000 nid=0x3860 runnable 

"GC task thread#1 (ParallelGC)" os_prio= tid=0x0000000002f6b000 nid=0x2ab0 runnable 

"GC task thread#2 (ParallelGC)" os_prio= tid=0x0000000002f6c800 nid=0x507c runnable 

"GC task thread#3 (ParallelGC)" os_prio= tid=0x0000000002f6e000 nid=0x3458 runnable 

"VM Periodic Task Thread" os_prio= tid=0x00000000195f0000 nid=0x3814 waiting on condition 

JNI global references:

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原始发表：2020-01-27，如有侵权请联系 cloudcommunity@tencent.com 删除

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