创建名为"{java}"的线程(即轻量级进程)是为了什么? [英] What are threads (i.e. lightweight processes) named `{java}` created for?
问题描述
我写了一个Java程序，它会睡一会儿:
I wrote a Java program that sleeps for a while:
package com.mycompany.app;
import java.lang.System;
import java.util.concurrent.TimeUnit;
public class Main {
public static void main(String[] args) {
System.out.println("the current process's pid is " + ProcessHandle.current().pid());
try {
TimeUnit.SECONDS.sleep(200);
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println("Hello World!"); // Prints the string to the console.
}
}
我运行以下程序:
$ java -cp target com.mycompany.app.Main
the current process's pid is 10172
我检查了Ubuntu创建的运行它的过程:
I inspect the processes that Ubuntu creates to run it:
$ pstree -pau -l -G -s 10172
systemd,1 splash
└─lxterminal,3194,t
└─bash,12150
└─java,10172 -cp target com.mycompany.app.Main
├─{java},10173
├─{java},10174
├─{java},10175
├─{java},10176
├─{java},10177
├─{java},10178
├─{java},10179
├─{java},10180
├─{java},10181
├─{java},10182
├─{java},10183
├─{java},10184
├─{java},10185
├─{java},10186
├─{java},10187
├─{java},10188
├─{java},10189
└─{java},10190
- 为
{java}创建的那些线程(即轻量级进程)是做什么用的? - 是否可以使用一些命令从shell中运行哪些程序?
- 哪些进程(和LWP)正在运行JVM?
- 哪些进程(和LWP)正在运行我的Java程序?
- What are those threads (i.e. lightweight processes) named
{java}created for? - Is it possible to find out what programs they run from shell using some commands?
- Which processes (and LWPs) are running JVM?
- Which processes (and LWPs) are running my Java program?
推荐答案
所有这些线程都属于JVM.
运行jstack <pid>以获得线程列表.
All of these threads belong to JVM.
Run jstack <pid> to get the thread list.
"main" #1 prio=5 os_prio=0 cpu=150.00ms elapsed=8.04s tid=0x00007f9f90011000 nid=0x107 waiting on condition [0x00007f9f99f9f000]
java.lang.Thread.State: TIMED_WAITING (sleeping)
at java.lang.Thread.sleep(java.base@11.0.1/Native Method)
at java.lang.Thread.sleep(java.base@11.0.1/Thread.java:339)
at java.util.concurrent.TimeUnit.sleep(java.base@11.0.1/TimeUnit.java:446)
at com.mycompany.app.Main.main(Main.java:10)
"Reference Handler" #2 daemon prio=10 os_prio=0 cpu=0.00ms elapsed=7.95s tid=0x00007f9f901f9000 nid=0x10e waiting on condition [0x00007f9f6c10f000]
java.lang.Thread.State: RUNNABLE
at java.lang.ref.Reference.waitForReferencePendingList(java.base@11.0.1/Native Method)
at java.lang.ref.Reference.processPendingReferences(java.base@11.0.1/Reference.java:241)
at java.lang.ref.Reference$ReferenceHandler.run(java.base@11.0.1/Reference.java:213)
"Finalizer" #3 daemon prio=8 os_prio=0 cpu=0.00ms elapsed=7.95s tid=0x00007f9f901fd800 nid=0x10f in Object.wait() [0x00007f9f65fef000]
java.lang.Thread.State: WAITING (on object monitor)
at java.lang.Object.wait(java.base@11.0.1/Native Method)
- waiting on <0x0000000712108f80> (a java.lang.ref.ReferenceQueue$Lock)
at java.lang.ref.ReferenceQueue.remove(java.base@11.0.1/ReferenceQueue.java:155)
- waiting to re-lock in wait() <0x0000000712108f80> (a java.lang.ref.ReferenceQueue$Lock)
at java.lang.ref.ReferenceQueue.remove(java.base@11.0.1/ReferenceQueue.java:176)
at java.lang.ref.Finalizer$FinalizerThread.run(java.base@11.0.1/Finalizer.java:170)
"Signal Dispatcher" #4 daemon prio=9 os_prio=0 cpu=0.00ms elapsed=7.93s tid=0x00007f9f90210000 nid=0x110 runnable [0x0000000000000000]
java.lang.Thread.State: RUNNABLE
"C2 CompilerThread0" #5 daemon prio=9 os_prio=0 cpu=40.00ms elapsed=7.93s tid=0x00007f9f90212000 nid=0x111 waiting on condition [0x0000000000000000]
java.lang.Thread.State: RUNNABLE
No compile task
"C1 CompilerThread0" #7 daemon prio=9 os_prio=0 cpu=40.00ms elapsed=7.93s tid=0x00007f9f90214000 nid=0x112 waiting on condition [0x0000000000000000]
java.lang.Thread.State: RUNNABLE
No compile task
"Sweeper thread" #8 daemon prio=9 os_prio=0 cpu=10.00ms elapsed=7.93s tid=0x00007f9f90216000 nid=0x113 runnable [0x0000000000000000]
java.lang.Thread.State: RUNNABLE
"Service Thread" #9 daemon prio=9 os_prio=0 cpu=0.00ms elapsed=7.90s tid=0x00007f9f902d3800 nid=0x114 runnable [0x0000000000000000]
java.lang.Thread.State: RUNNABLE
"Common-Cleaner" #10 daemon prio=8 os_prio=0 cpu=0.00ms elapsed=7.89s tid=0x00007f9f902df800 nid=0x116 in Object.wait() [0x00007f9f656ef000]
java.lang.Thread.State: TIMED_WAITING (on object monitor)
at java.lang.Object.wait(java.base@11.0.1/Native Method)
- waiting on <0x0000000712002df0> (a java.lang.ref.ReferenceQueue$Lock)
at java.lang.ref.ReferenceQueue.remove(java.base@11.0.1/ReferenceQueue.java:155)
- waiting to re-lock in wait() <0x0000000712002df0> (a java.lang.ref.ReferenceQueue$Lock)
at jdk.internal.ref.CleanerImpl.run(java.base@11.0.1/CleanerImpl.java:148)
at java.lang.Thread.run(java.base@11.0.1/Thread.java:834)
at jdk.internal.misc.InnocuousThread.run(java.base@11.0.1/InnocuousThread.java:134)
"Attach Listener" #11 daemon prio=9 os_prio=0 cpu=0.00ms elapsed=0.21s tid=0x00007f9f44001000 nid=0x126 waiting on condition [0x0000000000000000]
java.lang.Thread.State: RUNNABLE
"VM Thread" os_prio=0 cpu=0.00ms elapsed=7.95s tid=0x00007f9f901f1000 nid=0x10d runnable
"GC Thread#0" os_prio=0 cpu=0.00ms elapsed=8.01s tid=0x00007f9f90038800 nid=0x108 runnable
"G1 Main Marker" os_prio=0 cpu=0.00ms elapsed=8.00s tid=0x00007f9f90097800 nid=0x109 runnable
"G1 Conc#0" os_prio=0 cpu=0.00ms elapsed=8.00s tid=0x00007f9f90099800 nid=0x10a runnable
"G1 Refine#0" os_prio=0 cpu=0.00ms elapsed=8.00s tid=0x00007f9f9018d000 nid=0x10b runnable
"G1 Young RemSet Sampling" os_prio=0 cpu=0.00ms elapsed=8.00s tid=0x00007f9f9018f000 nid=0x10c runnable
"VM Periodic Task Thread" os_prio=0 cpu=0.00ms elapsed=7.90s tid=0x00007f9f902d6000 nid=0x115 waiting on condition
此处nid是操作系统中线程的十六进制ID-您可以将其与pstree的输出匹配.
Here nid is the hexadecimal ID of a thread in the OS - you may match it to the output of pstree.
-
第一个名为
main的线程是执行代码的线程.
The first thread named
mainis the thread executing your code.
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
Reference Handler thread is responsible for adding Weak, Soft and Phantom references discovered by Garbage Collector into their registered ReferenceQueues.
Finalizer线程对准备完成的对象运行finalize方法.
Finalizer thread runs finalize method of the objects ready to be finalized.
Signal Dispatcher等待特定的OS信号并处理它们.特别是，它在SIGQUIT上进行线程转储，并在SIGTERM，SIGINT和SIGHUP上启动VM关闭过程.
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 and SIGHUP.
CompilerThreads执行字节码的JIT编译.
CompilerThreads perform JIT compilation of the bytecode.
Sweeper thread清除过时的编译方法.
Sweeper thread cleans up obsolete compiled methods.
Service Thread运行一些后台JVM任务:检测内存不足情况，清理StringTable和SymbolTable，发送延迟的JVMTI事件和GC通知等.
Service Thread runs several background JVM tasks: detects low memory condition, cleans up StringTable and SymbolTable, sends deferred JVMTI events and GC notifications and so on.
Common-Cleaner runs cleaning actions of java.lang.ref.Cleaner instances.
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.
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.
VM Thread运行需要安全点的内部VM操作.此类操作的示例包括反优化，类重新定义，有偏的锁吊销，线程转储，堆检查等.
VM Thread runs internal VM operations that require a safepoint. The examples of such operations are deoptimization, class redifinition, biased lock revocation, thread dump, heap inspection etc.
G1线程与垃圾回收有关.
G1 threads are involved in Garbage Collection.
VM Periodic Task Thread用于模拟计时器中断.
VM Periodic Task Thread is used to simulate timer interrupts.
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