守护程序线程和低优先级线程之间的区别 [英] Difference between a daemon thread and a low priority thread

问题描述

最近有人问我一个问题:

Recently I was asked a question:

我们已经有了setPriority()方法来将线程设置为低优先级. 那为什么我们需要一个守护线程.它们之间有什么区别?

We've got the setPriority() method to set a thread for low priority. Then why do we need a daemon thread. What's the difference between them?

将线程标记为守护程序是否会更改其调度?

Does marking a thread as daemon change its scheduling?

推荐答案

我们有setPriority()方法来将线程设置为低优先级.那为什么我们需要一个守护线程.它们之间有什么区别?

We've got the setPriority() method to set a thread for low priority. Then why do we need a daemon thread. What's the difference between them?

通常，守护进程线程与优先级无关.当所有用户非守护程序线程完成时，JVM将关闭.将线程标记为守护程序线程意味着在JVM退出时可以安全地将其杀死.

Typically, daemon threads have nothing to do with priority. The JVM shuts down when all user non-daemon threads finish. Marking a thread as a daemon thread means that it can be safely killed when the JVM exits.

优先级与调度有关–与一个线程相比，该线程与准备运行的其他线程相比，获得时间片的频率.您可以具有低优先级的守护程序线程或高优先级的守护程序线程.您可以具有低优先级和高优先级的非守护线程.顺便说一句，线程优先级仅适用于某些特定情况和某些体系结构，作为Java线程专家，我从不使用它们.

Priority is about scheduling – about how often a thread gets a time slice in comparison to other threads that are ready to run. You can have low priority daemon threads or high priority daemon threads. You can have non-daemon threads that are also low and high priority. As an aside, thread priorities only apply in certain specific situations and on certainly architectures and as a Java thread expert, I never use them.

至少在Java线程模型中，这些概念是正交的(相互独立).

The concepts are orthogonal (mutually independent) – at least in the Java thread model.

就何时创建​​线程守护程序而言，我将守护程序线程用于我不在乎JVM退出时是否中断的任何任务:保持活动线程，统计处理器，日志处理等.所有对应用程序至关重要的任务是非守护线程，必须专门中断该线程或发出以某种方式退出该信号的信号.

In terms of when to make a thread daemon, I use daemon threads for any tasks that I don't care if they are interrupted when the JVM quits: keep-alive threads, statistics processors, log handling, etc.. Everything mission critical to the application is a non-daemon thread that has to be specifically interrupted or signaled to quit somehow.

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