Should work on armv7 as well as armv8

android_ndk_thread_affinity.cpp

#include <sys/syscall.h>
#include <sys/types.h>
#include <pthread.h>
#include <unistd.h>
#include <errno.h>
#include <cstdio>

#ifndef CPU_SETSIZE

#define CPU_SETSIZE 1024
#define __NCPUBITS  (8 * sizeof (unsigned long))

#ifdef __ANDROID__
#define gettid() syscall(__NR_gettid)
#else
#define gettid() syscall(SYS_gettid)
#endif

typedef unsigned long int __cpu_mask;
# define __CPUELT(cpu)  ((cpu) / __NCPUBITS)
# define __CPUMASK(cpu) ((__cpu_mask) 1 << ((cpu) % __NCPUBITS))

typedef struct
{
    unsigned long __bits[CPU_SETSIZE / __NCPUBITS];
} cpu_set_t;

#define CPU_SET(cpu, cpusetp) \
     ((__cpu_mask *)((cpusetp)->__bits))[__CPUELT (cpu)] |= __CPUMASK (cpu)
#define CPU_ZERO(cpusetp) \
     memset((cpusetp), 0, sizeof(cpu_set_t))
#define CPU_ISSET(cpu, cpusetp) \
     ((((const __cpu_mask *)((cpusetp)->__bits))[__CPUELT (cpu)] & __CPUMASK (cpu))) != 0
#define CPU_CLR(cpu, cpusetp) \
     (((__cpu_mask *)((cpusetp)->__bits))[__CPUELT (cpu)] &= ~__CPUMASK (cpu))
#define DEFINED_HERE "yes"

#endif

#ifndef DEFINED_HERE
#define DEFINED_HERE "no"
#endif

void setCurrentThreadAffinityMask(cpu_set_t mask)
{
    int err, syscallres;
    pid_t pid = gettid();
    syscallres = syscall(__NR_sched_setaffinity, pid, sizeof(mask), &mask);
    if (syscallres)
    {
        err = errno;
        printf("Error in the syscall setaffinity: err=%d=0x%x", err, err);
    }
}
int getCPUCount()
{
    cpu_set_t cs;
    CPU_ZERO(&cs);
    int syscallres;
    syscallres = syscall(__NR_sched_setaffinity, 0, sizeof(cs), &cs);

    int count = 0;
    for (int i = 0; i < 100; i++)
    {
        if (CPU_ISSET(i, &cs))
            count++;
    }
    return count;
}
int main() {
    printf("%s", DEFINED_HERE);
    cpu_set_t mask;
    long long j = 0;
    int count  = getCPUCount();
    for (int i = 0; i < count; ++i) {
        CPU_ZERO(&mask);
        CPU_SET(i, &mask);
        setCurrentThreadAffinityMask(mask);
        printf("%d\n", i);
        while (1) {
            j++;
            if (j == 2000000000L) break;
        }
        j = 0;
    }
    return 0;
}