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      1 //===----------------------------------------------------------------------===//
      2 //
      3 //                     The LLVM Compiler Infrastructure
      4 //
      5 // This file is dual licensed under the MIT and the University of Illinois Open
      6 // Source Licenses. See LICENSE.TXT for details.
      7 //
      8 //===----------------------------------------------------------------------===//
      9 
     10 // <mutex>
     11 
     12 // template <class Mutex> class lock_guard;
     13 
     14 // explicit lock_guard(mutex_type& m);
     15 
     16 #include <mutex>
     17 #include <thread>
     18 #include <cstdlib>
     19 #include <cassert>
     20 
     21 std::mutex m;
     22 
     23 typedef std::chrono::system_clock Clock;
     24 typedef Clock::time_point time_point;
     25 typedef Clock::duration duration;
     26 typedef std::chrono::milliseconds ms;
     27 typedef std::chrono::nanoseconds ns;
     28 
     29 void f()
     30 {
     31     time_point t0 = Clock::now();
     32     time_point t1;
     33     {
     34     std::lock_guard<std::mutex> lg = m;
     35     t1 = Clock::now();
     36     }
     37     ns d = t1 - t0 - ms(250);
     38     assert(d < ns(2500000));  // within 2.5ms
     39 }
     40 
     41 int main()
     42 {
     43     m.lock();
     44     std::thread t(f);
     45     std::this_thread::sleep_for(ms(250));
     46     m.unlock();
     47     t.join();
     48 }
     49