static const size_t kFibers = 2;
    static const size_t kIterations = 100;

    size_t cs_count = 0;

    size_t thread_count = 0;

    auto routine = [&]() {
      for (size_t i = 0; i < kIterations; ++i) {
        while (thread_count++ > 0) {
        Yield();
        --thread_count;


        }
        Yield();
        ++cs_count;
        ASSERT_TRUE_M(cs_count <  3, "Too many critical sections");

        --thread_count;

      }