用简单的Java代码创建的这些JVM守护程序线程是什么?

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问题描述

我有一个非常简单的Java应用程序，它只是创建一个对象，并在无限循环内对其调用所有函数

I have so simple java app, It simply creates an object, calls a function on it all these inside an infinite loop

public class h {
    public static void main( String[] args) {
        while(true) {
            B b = new B();
            b.print();
        }
    }
}

class B {
    public void print() {
        System.out.println("Hello I'am class B");
    }
}

打开jvisualvm，我看到JVM创建了10个线程，只有一个活动线程(即主线程)和9个守护程序.

Opening the jvisualvm I see 10 threads created by the JVM, only one active which is the main thread and 9 daemons.

这9个线程的用途是什么?

What is the usage of these 9 threads ?

并且其中有人与垃圾收集有任何关系吗?

And is anyone of them related to Garabage collection in any manner ?

注意:java -version的输出:

java version "1.8.0_112"
Java(TM) SE Runtime Environment (build 1.8.0_112-b15)
Java HotSpot(TM) 64-Bit Server VM (build 25.112-b15, mixed mode)

OS:Arch Linux 4.8.6-1

OS : Arch Linux 4.8.6-1

推荐答案

Reference Handler 线程负责将垃圾收集器发现的弱引用，软引用和幻像引用添加到已注册的参考队列.
Finalizer 线程对准备完成的对象运行finalize方法.
Signal Dispatcher 等待特定的OS信号并处理它们.特别是，它会在SIGQUIT上进行线程转储，并在SIGTERM，SIGINT，SIGHUP上启动VM关闭过程.
Attach Listener 线程支持动态附加机制.它侦听传入的动态附加连接并执行VM命令.例如，jstack，jmap和jcmd实用程序使用它.
RMI TCP Accept线程显然接受新的RMI连接.
RMI TCP Connection线程服务已建立的RMI连接.
RMI Scheduler运行RMI后台任务，例如 DGC .
JMX server connection timeout线程在需要时终止JMX连接.

Reference Handler thread is responsible for adding Weak, Soft and Phantom references discovered by Garbage Collector into their registered ReferenceQueues.
Finalizer thread runs finalize method of the objects ready to be finalized.
Signal Dispatcher waits for specific OS signals and handles them. In particular, it makes thread dump on SIGQUIT, and also initiates VM shutdown process on SIGTERM, SIGINT, SIGHUP.
Attach Listener thread supports Dynamic Attach mechanism. It listens for incoming Dynamic Attach connections and executes VM commands. For example, it is used by jstack, jmap and jcmd utilities.
RMI TCP Accept thread obviously accepts new RMI connections.
RMI TCP Connection threads serve the established RMI connections.
RMI Scheduler runs RMI background tasks like DGC.
JMX server connection timeout thread terminates JMX connetion when needed.

Reference Handler，Finalizer和部分RMI Scheduler与GC相关.

Reference Handler, Finalizer and partly RMI Scheduler are related to GC.

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