Is there an advantage of the operating system understanding the characteristics of how a thread may be used?

Question

Is there an advantage of the operating system understanding the characteristics of how a thread may be used? For example, what if there were a way in Java when creating a new thread to indicate that it would be used for intensive CPU calculations vs will block for I/O. Wouldn't thread scheduling improve if this were a capability?

Answer 1

I'm not sure what you're actually expecting the OS to do with the information that a thread is I/O or compute. The things which actually make the most difference to how threads get scheduled (ie thread priority and thread CPU affinity) are already exposed by APIs (and support for NUMA aspects are starting to appear in mainstream OS APIs too).

If by a "compute thread" you mean it's something doing background processing and less important than a GUI thread (from the point of view of maintaining app responsiveness) probably the most useful thing you can do is lower the priority of the compute threads a little.

Answer 2

That's what OS processes do. The OS has sophisticated scheduling for the processes. The OS tracks I/O use and CPU use and dynamically adjusts priorities so that CPU-intensive processing doesn't interfere with I/O.

If you want those features, use a proper OS process.

Answer 3

Is that even necessary? Threads blocking on I/O will cause CPU-intensive threads to run. The operating system decides how to schedule threads. AFAIK there's no way to give any hints with Java.

Answer 4

Yes, it is very important to understand them specially if you are one of those architects who like opening lot of threads, specially on windows.

Jeff Richter over at Wintellect has a library called PowerThreading. It is very useful if you are developing applications on .NET, but since you are talking about JAVA, it is still better to understand OS threads, kernel models and how the interrupts work.