thread local bench

tls_bench.c

// gcc -O2 -Wall -pthread tls_bench.c -o tls_bench
// ./tls_bench <num_threads> <loop>
#include <stdio.h>
#include <stdlib.h>
#include <stdint.h>
#include <pthread.h>
#include <assert.h>
#include <stdatomic.h>

__thread int tls = -1; 
_Atomic uint32_t counter[8] = {0};
_Atomic uint32_t round_robin = 0;

void* counter_thread(void *args)
{
  const int loop = *(int*)args;
  if (tls == -1)
    tls = atomic_fetch_add_explicit(&round_robin, 1, memory_order_relaxed) % 8;

  printf("tls is %d\n", tls);

  for (int i = 0; i < loop; i++)
    atomic_fetch_add_explicit(&counter[tls], 1, memory_order_relaxed);
  return NULL;
}

int main(int argc, char** argv)
{
  assert(argc == 3);
  int num_threads = atoi(argv[1]);
  int loop = atoi(argv[2]);
  pthread_t *threads = alloca(sizeof(pthread_t)*num_threads);

  for (int i = 0; i < num_threads; i++)
    assert(!pthread_create(&threads[i], NULL, counter_thread, &loop));

  for (int i = 0; i < num_threads; i++)
    assert(!pthread_join(threads[i], NULL));

  for (int i = 0; i < 8; i++)
    printf("Atomic counter[%d] = %d\n", i,
      atomic_load_explicit(&counter[i], memory_order_relaxed));
  return 0;
}