multithreading - How are Java Thread priorities translated to an OS thread priority?

Question

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.

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.

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

Answer 1

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

Solaris

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

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.

Linux

• 1 – 10 ? 4 – -5 (nice values)

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

Windows

• 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