compiler-rt/lib/tsan/benchmarks/start_many_threads.cpp

   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
  17 pthread_barrier_t all_threads_ready;
  18
  19 void* Thread(void *unused) {
  20   pthread_barrier_wait(&all_threads_ready);
  21   return 0;
  22 }
  23
  24 int 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 }