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
  // ALLOW_RETRIES: 2
  
  // <mutex>
  
  // template <class Mutex> class unique_lock;
  
  // void lock();
  
  #include <mutex>
  #include <thread>
  #include <cstdlib>
  #include <cassert>
  
  #include "make_test_thread.h"
  #include "test_macros.h"
  
  std::mutex m;
  
  typedef std::chrono::system_clock Clock;
  typedef Clock::time_point time_point;
  typedef Clock::duration duration;
  typedef std::chrono::milliseconds ms;
  typedef std::chrono::nanoseconds ns;
  
  void f()
  {
      std::unique_lock<std::mutex> lk(m, std::defer_lock);
      time_point t0 = Clock::now();
      lk.lock();
      time_point t1 = Clock::now();
      assert(lk.owns_lock() == true);
      ns d = t1 - t0 - ms(250);
      assert(d < ms(25));  // within 25ms
  #ifndef TEST_HAS_NO_EXCEPTIONS
      try
      {
          lk.lock();
          assert(false);
      }
      catch (std::system_error& e)
      {
          assert(e.code().value() == EDEADLK);
      }
  #endif
      lk.unlock();
      lk.release();
  #ifndef TEST_HAS_NO_EXCEPTIONS
      try
      {
          lk.lock();
          assert(false);
      }
      catch (std::system_error& e)
      {
          assert(e.code().value() == EPERM);
      }
  #endif
  }
  
  int main(int, char**)
  {
      m.lock();
      std::thread t = support::make_test_thread(f);
      std::this_thread::sleep_for(ms(250));
      m.unlock();
      t.join();
  
    return 0;
  }
  