1 #include <utility>
2 #include <iostream>
3 #include <future>
4 #include <thread>
5 #include <utility>
6
7 std::mutex coutMutex;
8
9 long double getDifference(const std::chrono::steady_clock::time_point& tp1,const std::chrono::steady_clock::time_point& tp2){
0     auto diff= tp2- tp1;
1     auto res= std::chrono::duration <double, std::milli> (diff).count();
2     return res;
3 }
4
5 int producer(std::promise<int>&& prom){
6     std::cout << "PRODUCING THE VALUE 2011\n\n";
7     std::this_thread::sleep_for(std::chrono::seconds(5));
8     prom.set_value(2011);
9 }
0
1 void consumer(std::shared_future<int> fut,std::chrono::steady_clock::duration dur){
2     auto start = std::chrono::steady_clock::now();
3     std::future_status status= fut.wait_until(std::chrono::steady_clock::now() + dur);
4     if ( status == std::future_status::ready ){
5         std::lock_guard<std::mutex> lockCout(coutMutex);
6         std::cout << std::this_thread::get_id() << " ready => Result: " << fut.get() << std::endl;
7     }
8     else{
9         std::lock_guard<std::mutex> lockCout(coutMutex);
0         std::cout << std::this_thread::get_id() << " stopped waiting." << std::endl;
1     }
2     auto end= std::chrono::steady_clock::now();
3     std::lock_guard<std::mutex> lockCout(coutMutex);
4     std::cout << std::this_thread::get_id() << " waiting time: " << getDifference(start,end) << " ms" << std::endl;
5 }
6
7 void consumePeriodically(std::shared_future<int> fut){
8     auto start = std::chrono::steady_clock::now();
9     std::future_status status;
0     do {
1         std::this_thread::sleep_for(std::chrono::milliseconds(700));
2         status = fut.wait_for(std::chrono::seconds(0));
3         if (status == std::future_status::timeout) {
4             std::lock_guard<std::mutex> lockCout(coutMutex);
5             std::cout << "     " << std::this_thread::get_id() << " still waiting." << std::endl;
6         }
7         if (status == std::future_status::ready) {
8             std::lock_guard<std::mutex> lockCout(coutMutex);
9             std::cout << "     " << std::this_thread::get_id() << " waiting done => Result: " << fut.get() << std::endl;
0         }
1     } while (status != std::future_status::ready);
2     auto end= std::chrono::steady_clock::now();
3     std::lock_guard<std::mutex> lockCout(coutMutex);
4     std::cout << "     " << std::this_thread::get_id() << " waiting time: " << getDifference(start,end) << " ms" << std::endl;
5 }
6
7 void consumeWithBackoff(std::shared_future<int> fut){
8     auto start = std::chrono::steady_clock::now();
9     std::future_status status;
0     auto dur= std::chrono::milliseconds(1);
1     do {
2         std::this_thread::sleep_for(dur);
3         status = fut.wait_for(std::chrono::seconds(0));
4         dur *= 2;
5         if (status == std::future_status::timeout) {
6             std::lock_guard<std::mutex> lockCout(coutMutex);
7             std::cout << "         " << std::this_thread::get_id() << " still waiting." << std::endl;
8         }
9         if (status == std::future_status::ready) {
0             std::lock_guard<std::mutex> lockCout(coutMutex);
1             std::cout << "         " << std::this_thread::get_id() << " waiting done => Result: " << fut.get() << std::endl;
2         }
3     } while (status != std::future_status::ready);
4     auto end= std::chrono::steady_clock::now();
5     std::lock_guard<std::mutex> lockCout(coutMutex);
6     std::cout << "         " << std::this_thread::get_id() <<
      " waiting time: " << getDifference(start,end) << " ms" << std::endl;
7 }
8
9 int main(){
0
1     std::cout << std::endl;
2
3     std::promise<int> prom;
4     std::shared_future<int> future= prom.get_future();
5     std::thread producerThread(producer,std::move(prom));
6
7     std::thread consumerThread1(consumer,future,std::chrono::seconds(4));
8     std::thread consumerThread2(consumer,future,std::chrono::seconds(20));
9     std::thread consumerThread3(consumePeriodically,future);
0     std::thread consumerThread4(consumeWithBackoff,future);
1
2     consumerThread1.join();
3     consumerThread2.join();
4     consumerThread3.join();
5     consumerThread4.join();
6     producerThread.join();
7
8     std::cout << std::endl;
9
0 }