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(barrier: &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(nptr: argv[1]);
30 } else {
31 printf(format: "Usage: %s n_threads\n", argv[0]);
32 return 1;
33 }
34 printf(format: "%s: n_threads=%d\n", __FILE__, n_threads);
35
36 pthread_barrier_init(barrier: &all_threads_ready, NULL, count: 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(newthread: &t[i], attr: 0, start_routine: Thread, arg: (void*)i);
41 assert(status == 0);
42 }
43 // sleep(5); // FIXME: simplify measuring the memory usage.
44 pthread_barrier_wait(barrier: &all_threads_ready);
45 for (int i = 0; i < n_threads; i++) {
46 pthread_join(th: t[i], thread_return: 0);
47 }
48 // sleep(5); // FIXME: simplify measuring the memory usage.
49 delete [] t;
50
51 return 0;
52}
53

source code of compiler-rt/lib/tsan/benchmarks/start_many_threads.cpp