text: // RUN: %clang_tsan %s -o %t
  // RUN: %run %t 2>&1 | FileCheck %s --implicit-check-not='ThreadSanitizer'
  
  #include <dispatch/dispatch.h>
  
  #include <stdio.h>
  
  void notify_callback(void *context) {
    // Do nothing.
  }
  
  int main() {
    fprintf(stderr, "Hello world.");
  
    dispatch_queue_t q = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);
  
    for (int i = 0; i < 300000; i++) {
      dispatch_group_t g = dispatch_group_create();
      dispatch_group_enter(g);
      dispatch_async(q, ^{
        dispatch_group_leave(g);
      });
      dispatch_group_notify(g, q, ^{
        // Do nothing.
      });
      dispatch_release(g);
    }
  
    for (int i = 0; i < 300000; i++) {
      dispatch_group_t g = dispatch_group_create();
      dispatch_group_enter(g);
      dispatch_async(q, ^{
        dispatch_group_leave(g);
      });
      dispatch_group_notify_f(g, q, NULL, &notify_callback);
      dispatch_release(g);
    }
  
    fprintf(stderr, "Done.");
  }
  
  // CHECK: Hello world.
  // CHECK: Done.
  