Obtaining thread Core affinity in C++ 11 through pthreads

Question

I'm trying to set core affinity (Thread #1 goes on first core, Thread #2 goes on second core, ...) while using std::thread in C++ 11.

I've already searched around various topics and on the internet and it seems C++ 11 API doesn't provide such low level feature.

On the other hand, pthreads come with pthread_setaffinity_np which would be useful if I could get the "pthread_t" value of my std::thread (I don't know if this is human reasonable or at least legitimate asking for it).

An example program of what I'd want to have in the end is this:

#include <thread>
#include <pthread.h>
#include <iostream>
#include <stdio.h>
#include <stdlib.h>

#define CORE_NO 8

using namespace std;

void run(int id) {
    cout << "Hi! I'm thread " << id << endl;
    // thread function goes here
}

int main() {
    cpu_set_t cpu_set;

    CPU_ZERO(&cpu_set);
    for(int i=0; i<CORE_NO; i++)
        CPU_SET(i, &cpu_set);

    thread t1(run, 1);

    // obtaining pthread_t from t1

    /*
    pthread_t this_tid = foo(t1);
    pthread_setaffinity_np(this_tid, sizeof(cpu_set_t), &cpu_set);
    */

    t1.join();

    return 0;
}

I'd really prefer not to change the whole architecture of my project (which must provide such characteristic). I've now a massive use of std::thread but I can use pthread API in addition as well, as you have seen in the example.

Is there a way for me to solve this problem?

Answer 1

You can get the native handle for the thread with the native_handle function.

The example in the linked reference even uses this to call pthread functions.

Answer 2

I do not know if it is a suitable approach in your case, but what I usually do is to call the affinity primitives from within the thread. E.g., I place a snippet of code similar to this one somewhere at the beginning of the threaded function:

const int err = pthread_setaffinity_np(pthread_self(),...);

The call to pthread_self() will return the ID of the calling thread.