text: //===----------------------------------------------------------------------===//
  //
  // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
  // See https://llvm.org/LICENSE.txt for license information.
  // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
  //
  //===----------------------------------------------------------------------===//
  //
  // UNSUPPORTED: libcpp-has-no-threads
  // UNSUPPORTED: c++98, c++03, c++11
  // XFAIL: dylib-has-no-shared_mutex
  
  // ALLOW_RETRIES: 2
  
  // <shared_mutex>
  
  // class timed_mutex;
  
  // template <class Rep, class Period>
  //   shared_lock(mutex_type& m, const chrono::duration<Rep, Period>& rel_time);
  
  #include <shared_mutex>
  #include <thread>
  #include <vector>
  #include <cstdlib>
  #include <cassert>
  
  #include "test_macros.h"
  
  std::shared_timed_mutex m;
  
  typedef std::chrono::steady_clock Clock;
  typedef Clock::time_point time_point;
  typedef Clock::duration duration;
  typedef std::chrono::milliseconds ms;
  typedef std::chrono::nanoseconds ns;
  
  ms WaitTime = ms(250);
  
  // Thread sanitizer causes more overhead and will sometimes cause this test
  // to fail. To prevent this we give Thread sanitizer more time to complete the
  // test.
  #if !defined(TEST_HAS_SANITIZERS)
  ms Tolerance = ms(50);
  #else
  ms Tolerance = ms(50 * 5);
  #endif
  
  
  void f1()
  {
      time_point t0 = Clock::now();
      std::shared_lock<std::shared_timed_mutex> lk(m, WaitTime + Tolerance);
      assert(lk.owns_lock() == true);
      time_point t1 = Clock::now();
      ns d = t1 - t0 - WaitTime;
      assert(d < Tolerance);  // within 50ms
  }
  
  void f2()
  {
      time_point t0 = Clock::now();
      std::shared_lock<std::shared_timed_mutex> lk(m, WaitTime);
      assert(lk.owns_lock() == false);
      time_point t1 = Clock::now();
      ns d = t1 - t0 - WaitTime;
      assert(d < Tolerance);  // within 50ms
  }
  
  int main(int, char**)
  {
      {
          m.lock();
          std::vector<std::thread> v;
          for (int i = 0; i < 5; ++i)
              v.push_back(std::thread(f1));
          std::this_thread::sleep_for(WaitTime);
          m.unlock();
          for (auto& t : v)
              t.join();
      }
      {
          m.lock();
          std::vector<std::thread> v;
          for (int i = 0; i < 5; ++i)
              v.push_back(std::thread(f2));
          std::this_thread::sleep_for(WaitTime + Tolerance);
          m.unlock();
          for (auto& t : v)
              t.join();
      }
  
    return 0;
  }
  