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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 // lock_guard(mutex_type& m, adopt_lock_t);
     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     m.lock();
     35     std::lock_guard<std::mutex> lg(m, std::adopt_lock);
     36     t1 = Clock::now();
     37     }
     38     ns d = t1 - t0 - ms(250);
     39     assert(d < ms(50));  // within 50ms
     40 }
     41 
     42 int main()
     43 {
     44     m.lock();
     45     std::thread t(f);
     46     std::this_thread::sleep_for(ms(250));
     47     m.unlock();
     48     t.join();
     49 }
     50