Java 线程优先级如何转换为 OS 线程优先级?

2022-01-11 00:00:00 operating-system multithreading java

Java API 线程优先级 (1-10) 如何转换为操作系统级别的优先级，因为大多数操作系统没有与此匹配的线程优先级(在数量方面).

How are the java API thread priorities (1-10) gets translated to the OS level priorities since most OS don't have thread priority levels (in terms of number) which match this.

因此请记住，是否存在两个或多个具有不同优先级的线程最终在操作系统级别获得相同优先级的情况.

So keeping in mind , can there be a scenario when two or more threads with different priorities eventually get the same priority at OS level.

请澄清，如果我的理解有一些更正.

Please clarify, if I there is some correction in my understanding.

推荐答案

确实，某些优先级可以映射到相同的本机"优先级.以下是列表(基于 OpenJDK 6 中的 Hotspot 代码):

Indeed, some priority levels can map to the same "native" priority level. Here's the list (based on the Hotspot code in OpenJDK 6):

  • 1 ⇒ 0
  • 2 ⇒ 32
  • 3 ⇒ 64
  • 4 ⇒ 96
  • 5 – 10 ⇒ 127

值得注意的是，在 Solaris 上，您不能将线程优先级提高到高于正常水平，只能降低它:5 的优先级值与任何更高的值相同.

Of note is that on Solaris, you can't raise the thread priority above normal, only lower it: the priority value for 5 is the same as any of the higher values.

  • 1 – 10 ⇒ 4 – -5(nice 值)

值得注意的是，在 Linux 上，Java 中不同的线程优先级确实映射到本机级别的不同优先级值.

Of note is that on Linux, different thread priorities in Java do map to distinct priority values at native level.

  • 1 – 2 ⇒ THREAD_PRIORITY_LOWEST
  • 3 – 4 ⇒ THREAD_PRIORITY_BELOW_NORMAL
  • 5 – 6 ⇒ THREAD_PRIORITY_NORMAL
  • 7 – 8 ⇒ THREAD_PRIORITY_ABOVE_NORMAL
  • 9 – 10 ⇒ THREAD_PRIORITY_HIGHEST

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