How to detect whether a core has been bound in C/C++?

Question

I coded a program that needs to run independently on a core to gain high performance. And, I need to run multiple such programs on a single machine.

So, I would like to know is there a way to detect whether a core is bound or not.

With that, a program can attempt to bind from core 0 and try the next one if it finds that the core is already bound.

I tried to use sched_setaffinity() to get exclusive access on a core. But it seems not to work. Here is my code:

#define _GNU_SOURCE
#include <assert.h>
#include <sched.h>
#include <stdbool.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>

void print_affinity() {
    cpu_set_t mask;
    long nproc, i;

    if (sched_getaffinity(0, sizeof(cpu_set_t), &mask) == -1) {
        perror("sched_getaffinity");
        assert(false);
    }
    nproc = sysconf(_SC_NPROCESSORS_ONLN);
    printf("sched_getaffinity = ");
    for (i = 0; i < nproc; i++) {
        printf("%d ", CPU_ISSET(i, &mask));
    }
    printf("\n");
}

int main(void) {
    cpu_set_t mask;

    print_affinity();
    printf("sched_getcpu = %d\n", sched_getcpu());
    CPU_ZERO(&mask);
    CPU_SET(0, &mask);
    if (sched_setaffinity(0, sizeof(cpu_set_t), &mask) == -1) {
        perror("sched_setaffinity");
        assert(false);
    }
    print_affinity();
    printf("sched_getcpu = %d\n", sched_getcpu());
    while(true){

    }
    return EXIT_SUCCESS;
}

I run the program in two terminals. My expectation is that the first program will bind to core 0 while the second program will see the core 0 is bound (by calling sched_getaffinity)

However, it seems that the second program can't be aware that core 0 is bound, i.e., the first print_affinity() of the second program prints out that all bits of the CPU mask are 1.

Thanks.