blocks|key|3919686|text|当所有正在运行的线程都是守护线程时，JVM退出。所以想象一下，你正在写一个简单的游戏，你的main方法一直循环到你决定退出。想象一下，在游戏开始时，你启动了一个线程，它将无休止地轮询一些网站以触发警报。您可能希望JVM在您决定结束游戏时退出。您不希望无休止的轮询阻止游戏结束。因此，您将此轮询线程设置为守护线程。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|3919687|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|D|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|E|8|@]|9|@]|A|$]]]|C|$]]

The JVM exits when all the running threads are daemon threads. So imagine you're writing a simple game where your main method loops until you decide to quit. And imagine that at the start of the game, you start a thread that will endlessly poll some website to trigger alerts. You would like the JVM to exit when you decide to end the game. You don't want the endless polling to prevent the game from ending. So you make this polling thread a daemon thread.

blocks|key|3919700|text|当所有“正常”线程都终止时，JVM会自动终止一个守护线程。普通线程永远不会自动终止。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|3919701|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|D|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|E|8|@]|9|@]|A|$]]]|C|$]]

A Deamon thread is automatically terminated by the JVM when all "normal" threads are terminated. Normal threads are never automatically terminated.

blocks|key|2020365|text|将用户线程设置为守护进程的主要用例是，您希望以用户线程的方式提供给消费者而不需要任何用户交互的服务。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2020366|因此，在用户线程存在之前，JVM可以保证守护线程持续运行。你可以找到像GC，UI+Thread这样的例子。这些是守护进程。|2020367|希望能有所帮助。|2020368|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|H|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|I|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|J|8|@]|9|@]|A|$]]|$1|F|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|G|$]]

Services that you wish to offer to your consumers without any user-interation by way of essentially user-threads form the primary use-case for setting a user thread as a daemon.

As a consequence, until user-threads exist JVM gurantees that daemon threads run continously. You can find examples like GC, UI Thread etc.. those are daemons.

Hope it helps.

blocks|key|2020438|text|正如其他人所指出的那样，守护程序线程不会阻止JVM在程序结束时退出，而该线程仍在运行。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2020439|通常，您不希望创建守护进程线程，除非您绝对确定该线程没有副作用。由于您不知道线程何时停止，所以终结器块不会运行，任何堆栈也不会展开。因此，尽量避免在守护程序线程中使用IO操作，因为它可能会损坏数据。|2020440|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|F|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|G|8|@]|9|@]|A|$]]|$1|D|3|-4|5|6|7|H|8|@]|9|@]|A|$]]]|E|$]]

As other have pointed, a daemon thread does not prevent the JVM from exiting when the program finishes when this thread is still running.

In general you'd rather not create daemon threads, unless you are absolutely certain the thread has no side effects. Since you can't tell when the thread stops, finalizer blocks are not run, nor are any stack unwound. So try avoiding using IO operations in daemon threads because it can corrupt data.

blocks|key|2020406|text|通常，当程序的所有线程都退出run()方法时，程序就会终止。守护程序线程不会阻止程序终止，即使它们仍在运行，即执行run()。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|2020407|因此，如果您不希望在线程仍在运行时阻止程序终止，则应使用守护程序线程。例如，这是典型的长周期任务，但实际上很大程度上取决于您的程序、您的设计和您的品味。|2020408|entityMap^0|E|5|1L|5|0|0^^$0|@$1|2|3|4|5|6|7|J|8|@$9|K|A|L|B|C]|$9|M|A|N|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|O|8|@]|D|@]|E|$]]|$1|H|3|-4|5|6|7|P|8|@]|D|@]|E|$]]]|I|$]]

Normally program terminates when all its threads exited their <code>run()</code> method. Daemon threads do not prevent program to terminate even if they are still running, i.e. executing <code>run()</code>.

So, you should use daemon thread if you wish not to prevent program termination when the thread is still running. It is typical for example for long-time periodic tasks but actually depend very much on your program, your design and your taste.

blocks|key|2020488|text|Java中的守护程序线程就像是在与守护程序线程相同的进程中运行的其他线程或对象的服务提供者。守护程序线程用于后台支持任务，并且仅在普通线程执行时才需要。如果普通线程没有运行，而其余线程是守护进程线程，则解释器退出。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2020489|创建新线程时，它会继承其父线程的守护进程状态。普通线程和守护程序线程在退出时发生的情况有所不同。当JVM暂停时，任何剩余的守护进程线程都会被放弃:最终块不会执行，堆栈也不会展开-+JVM只是退出。因此，应谨慎使用守护程序线程，并且将它们用于可能执行任何类型的I/O的任务是危险的。|2020490|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|F|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|G|8|@]|9|@]|A|$]]|$1|D|3|-4|5|6|7|H|8|@]|9|@]|A|$]]]|E|$]]

Daemon threads in Java are like a service providers for other threads or objects running in the same process as the daemon thread. Daemon threads are used for background supporting tasks and are only needed while normal threads are executing. If normal threads are not running and remaining threads are daemon threads then the interpreter exits.

When a new thread is created it inherits the daemon status of its parent. Normal thread and daemon threads differ in what happens when they exit. When the JVM halts any remaining daemon threads are abandoned: finally blocks are not executed, stacks are not unwound – JVM just exits. Due to this reason daemon threads should be used sparingly and it is dangerous to use them for tasks that might perform any sort of I/O.

blocks|key|2020465|text|我把它们和定时器一起用来删除那些不能立即删除的文件。也就是说，我生成.exe文件，运行它们，然后删除它们。但executable.delete失败的可能性有50%25，似乎是因为图像仍然被终止中的进程阻止。只有在进程完全完成后，才能可靠地删除可执行镜像。但是，你永远不会知道这需要多长时间。因此，您可以设置.deleteOnExit而不是.delete。但是，您也不希望等到java机器终止。这可能会花费很长时间，你不会想要数百万个无用的愚蠢的.exe文件，这些文件你不再需要，挂在文件系统中。因此，您可以在计时器中安排executable.delete在一到两秒后发生。但是，计时器不能是普通线程。如果是这样，它将阻止您的程序终止，即使没有要删除的文件。不过，我可以很容易地将其设为守护进程，因为定时器是否删除我的文件无关紧要--文件将以任何一种方式被删除:通过守护进程或java+exit。我认为这是对守护进程的完美使用。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|2020466|entityMap^0|1I|H|0^^$0|@$1|2|3|4|5|6|7|H|8|@$9|I|A|J|B|C]]|D|@]|E|$]]|$1|F|3|-4|5|6|7|K|8|@]|D|@]|E|$]]]|G|$]]

I used them with Timer to delete files that cannot be deleted immediately. That is, I generate .exe files, run and then delete them. But there is 50% chance that <code>executable.delete</code> fails, seemingly because image is still blocked by the process in termination. You can reliably delete executable image only after process has finished completely. But, you never know how long it takes. You set .deleteOnExit therefore instead of .delete. But, you do not want to wait until java machine terminates also. It can take very long and you do not want millions of useless stupid .exe files, that you do not need anymore, hanging in the file system. You therefore schedule executable.delete in the timer to happen one-two seconds later. The timer however cannot be usual thread. If it is so, it will block your program from terminating even if there are no files to delete. I can easily make it daemon however because whether my files are deleted or not by timer is immaterial -- the files will be removed either way: either by daemon or java exit. I think it is perfect use of daemon.

I know that Deamon threads background threads. We can create our own daemon thread by calling <code>setDaemon(true)</code>. 

My question is: why and when do we need to create our thread as daemon thread?

When are daemon threads useful?

翻译质量差，导致语言生硬或混乱。

没有提供实际的解决方法或示例。

解答不清晰，无法理解或解决问题。

页面排版不美观，阅读体验差。

文章

问答

视频

学习中心

腾讯云实验室

直播

竞赛

腾讯云代码分析专区

腾讯iOA零信任安全管理系统专区

腾讯云架构师技术同盟交流圈

腾讯云数据库专区

腾讯云顾问专区

腾讯云原生专区

腾讯混元专区

腾讯云TCE专区

腾讯云Lighthouse专区

腾讯云HAI专区

腾讯云Edgeone专区

腾讯云存储专区

腾讯云智能专区

腾讯轻联专区 

腾讯云开发专区

TAPD专区

腾讯轻量云游戏服专区

腾讯云最具价值专家

腾讯云架构师技术同盟

腾讯云创作之星

腾讯云开发者先锋

腾讯云代码助手

云原生构建

TAPD 敏捷项目管理

Cloud Studio

SDK中心

API中心

命令行工具

涵盖代码开发、场景应用、自动测试全流程，助你从零构建专属AI助手

一站式MCP教程库，解锁AI应用新玩法

我知道守护线程后台线程。我们可以通过调用setDaemon(true)来创建我们自己的守护线程。我的问题是:为什么以及何时需要将我们的线程创建为守护线程？

问什么时候守护线程有用？
EN

回答 7

Stack Overflow用户

Stack Overflow用户

Stack Overflow用户

社区

活动

圈层

关于

腾讯云开发者

热门产品

热门推荐

更多推荐

问什么时候守护线程有用？EN

回答 7

Stack Overflow用户

Stack Overflow用户

Stack Overflow用户

社区

活动

圈层

关于

腾讯云开发者

热门产品

热门推荐

更多推荐

问什么时候守护线程有用？
EN