message: Synchronize test
diff: @@ -174,20 +174,27 @@ CAF_TEST(send and receive) {
  }
  CAF_TEST(shutdown) {
  - auto run_mpx = [=] {
  + std::mutex m;
  + std::condition_variable cv;
  + bool thread_id_set = false;
  + auto run_mpx = [&] {
  + std::unique_lock<std::mutex> lk(m);
  mpx->set_thread_id();
  + thread_id_set = true;
  + lk.unlock();
  + cv.notify_one();
  mpx->run();
  };
  CAF_REQUIRE_EQUAL(mpx->init(), none);
  - std::thread mpx_thread{run_mpx};
  auto sockets = unbox(make_stream_socket_pair());
  auto alice = make_counted<dummy_manager>(manager_count, sockets.first, mpx);
  auto bob = make_counted<dummy_manager>(manager_count, sockets.second, mpx);
  alice->register_reading();
  bob->register_reading();
  - while (mpx->num_socket_managers() != 3)
  - ; // nop
  CAF_REQUIRE_EQUAL(mpx->num_socket_managers(), 3u);
  + std::thread mpx_thread{run_mpx};
  + std::unique_lock<std::mutex> lk(m);
  + cv.wait(lk, [&] { return thread_id_set; });
  mpx->shutdown();
  mpx_thread.join();
  CAF_REQUIRE_EQUAL(mpx->num_socket_managers(), 0u);
  