1// Mini-benchmark for creating a lot of threads.
2//
3// Some facts:
4// a) clang -O1 takes <15ms to start N=500 threads,
5//    consuming ~4MB more RAM than N=1.
6// b) clang -O1 -ftsan takes ~26s to start N=500 threads,
7//    eats 5GB more RAM than N=1 (which is somewhat expected but still a lot)
8//    but then it consumes ~4GB of extra memory when the threads shut down!
9//        (definitely not in the barrier_wait interceptor)
10//    Also, it takes 26s to run with N=500 vs just 1.1s to run with N=1.
11#include <assert.h>
12#include <pthread.h>
13#include <stdio.h>
14#include <stdlib.h>
15#include <unistd.h>
16
17pthread_barrier_t all_threads_ready;
18
19void* Thread(void *unused) {
20  pthread_barrier_wait(&all_threads_ready);
21  return 0;
22}
23
24int main(int argc, char **argv) {
25  int n_threads;
26  if (argc == 1) {
27    n_threads = 100;
28  } else if (argc == 2) {
29    n_threads = atoi(argv[1]);
30  } else {
31    printf("Usage: %s n_threads\n", argv[0]);
32    return 1;
33  }
34  printf("%s: n_threads=%d\n", __FILE__, n_threads);
35
36  pthread_barrier_init(&all_threads_ready, NULL, n_threads + 1);
37
38  pthread_t *t = new pthread_t[n_threads];
39  for (int i = 0; i < n_threads; i++) {
40    int status = pthread_create(&t[i], 0, Thread, (void*)i);
41    assert(status == 0);
42  }
43  // sleep(5);  // FIXME: simplify measuring the memory usage.
44  pthread_barrier_wait(&all_threads_ready);
45  for (int i = 0; i < n_threads; i++) {
46    pthread_join(t[i], 0);
47  }
48  // sleep(5);  // FIXME: simplify measuring the memory usage.
49  delete [] t;
50
51  return 0;
52}
53