How can you find the processor number a thread is running on?

Question

I have a memory heap manager which partitions the heap into different segments based on the number of processors on the system. Memory can only be allocated on the partition that goes with the currently running thread's processor. This will help allow different processors to continue running even if two different ones want to allocate memory at the same time, at least I believe.

I have found the function GetCurrentProcessorNumber() for Windows, but this only works on Windows Vista and later. Is there a method that works on Windows XP?

Also, can this be done with pthreads on a POSIX system?

Answer 1

For XP, a quick google as revealed this: https://www.cs.tcd.ie/Jeremy.Jones/GetCurrentProcessorNumberXP.htm Does this help?

Answer 2

From output of man sched_getcpu:

NAME
       sched_getcpu - determine CPU on which the calling thread is running

SYNOPSIS
       #define _GNU_SOURCE
       #include <utmpx.h>

       int sched_getcpu(void);

DESCRIPTION
   sched_getcpu() returns the number of the CPU
   on which the calling thread is currently executing.

RETURN VALUE
   On success, sched_getcpu() returns a non-negative CPU number.
   On error, -1 is returned and errno is set to indicate the error.

SEE ALSO
   getcpu(2)

Unfortunately, this is Linux specific. I doubt there is a portable way to do this.

Answer 3

This design smells bad to me. You seem to be making the assumption that a thread will stay associated with a specific CPU. That is not guaranteed. Yes, a thread may normally stay on a single CPU, but it doesn't have to, and eventually your program will have a thread that switches CPU's. It may not happen often, but eventually it will. If your design doesn't take this into account, then you will mostly likely eventually hit some sort of hard to trace bug.

Let me ask this question, what happens if memory is allocated on one CPU and freed on another? How will your heap handle that?