 //===----------------------------------------------------------------------===//
 //
 //                     The LLVM Compiler Infrastructure
 //
 // This file is dual licensed under the MIT and the University of Illinois Open
 // Source Licenses. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 //
 // UNSUPPORTED: libcpp-has-no-threads

 // <future>

 // class shared_future<R>

 // template <class Clock, class Duration>
 //   future_status
 //   wait_until(const chrono::time_point<Clock, Duration>& abs_time) const;

 #include <future>
 #include <atomic>
 #include <cassert>

 enum class WorkerThreadState { Uninitialized, AllowedToRun, Exiting };
 typedef std::chrono::milliseconds ms;

 std::atomic<WorkerThreadState> thread_state(WorkerThreadState::Uninitialized);

 void set_worker_thread_state(WorkerThreadState state)
 {
     thread_state.store(state, std::memory_order_relaxed);
 }

 void wait_for_worker_thread_state(WorkerThreadState state)
 {
     while (thread_state.load(std::memory_order_relaxed) != state);
 }

 void func1(std::promise<int> p)
 {
     wait_for_worker_thread_state(WorkerThreadState::AllowedToRun);
     p.set_value(3);
     set_worker_thread_state(WorkerThreadState::Exiting);
 }

 int j = 0;

 void func3(std::promise<int&> p)
 {
     wait_for_worker_thread_state(WorkerThreadState::AllowedToRun);
     j = 5;
     p.set_value(j);
     set_worker_thread_state(WorkerThreadState::Exiting);
 }

 void func5(std::promise<void> p)
 {
     wait_for_worker_thread_state(WorkerThreadState::AllowedToRun);
     p.set_value();
     set_worker_thread_state(WorkerThreadState::Exiting);
 }

 int main()
 {
     typedef std::chrono::high_resolution_clock Clock;
     {
         typedef int T;
         std::promise<T> p;
         std::shared_future<T> f = p.get_future();
         std::thread(func1, std::move(p)).detach();
         assert(f.valid());
         assert(f.wait_until(Clock::now() + ms(10)) == std::future_status::timeout);
         assert(f.valid());

         // allow the worker thread to produce the result and wait until the worker is done
         set_worker_thread_state(WorkerThreadState::AllowedToRun);
         wait_for_worker_thread_state(WorkerThreadState::Exiting);

         assert(f.wait_until(Clock::now() + ms(10)) == std::future_status::ready);
         assert(f.valid());
         Clock::time_point t0 = Clock::now();
         f.wait();
         Clock::time_point t1 = Clock::now();
         assert(f.valid());
         assert(t1-t0 < ms(5));
     }
     {
         typedef int& T;
         std::promise<T> p;
         std::shared_future<T> f = p.get_future();
         std::thread(func3, std::move(p)).detach();
         assert(f.valid());
         assert(f.wait_until(Clock::now() + ms(10)) == std::future_status::timeout);
         assert(f.valid());

         // allow the worker thread to produce the result and wait until the worker is done
         set_worker_thread_state(WorkerThreadState::AllowedToRun);
         wait_for_worker_thread_state(WorkerThreadState::Exiting);

         assert(f.wait_until(Clock::now() + ms(10)) == std::future_status::ready);
         assert(f.valid());
         Clock::time_point t0 = Clock::now();
         f.wait();
         Clock::time_point t1 = Clock::now();
         assert(f.valid());
         assert(t1-t0 < ms(5));
     }
     {
         typedef void T;
         std::promise<T> p;
         std::shared_future<T> f = p.get_future();
         std::thread(func5, std::move(p)).detach();
         assert(f.valid());
         assert(f.wait_until(Clock::now() + ms(10)) == std::future_status::timeout);
         assert(f.valid());

         // allow the worker thread to produce the result and wait until the worker is done
         set_worker_thread_state(WorkerThreadState::AllowedToRun);
         wait_for_worker_thread_state(WorkerThreadState::Exiting);

         assert(f.wait_until(Clock::now() + ms(10)) == std::future_status::ready);
         assert(f.valid());
         Clock::time_point t0 = Clock::now();
         f.wait();
         Clock::time_point t1 = Clock::now();
         assert(f.valid());
         assert(t1-t0 < ms(5));
     }
 }