Implement async::executor::wait_all

libs/async/include/psemek/async/executor.hpp

@@ -63,6 +63,8 @@ namespace psemek::async
 	template <typename T>
 	struct future
 	{
+		using result_type = T;
+
 		future() = default;
 		future(future&&) = default;
 
@@ -191,6 +193,12 @@ namespace psemek::async
 		template <typename TimePoint, typename F, typename ... Args>
 		auto dispatch_at(TimePoint time, auto_cancel_tag, F && f, Args && ... args);
 
+		// Create a future that waits for all the provided futures.
+		// The returned future's result_type is void if the argument
+		// futures' result_type is void, and vector<result_type> otherwise.
+		template <typename Iterator>
+		auto wait_all(Iterator begin, Iterator end);
+
 		virtual ~executor() {}
 	};
 
@@ -230,4 +238,29 @@ namespace psemek::async
 		return future<R>(state);
 	}
 
+	template <typename Iterator>
+	auto executor::wait_all(Iterator begin, Iterator end)
+	{
+		using R = decltype(begin->get());
+		return dispatch([begin, end]{
+			if constexpr (std::is_same_v<R, void>)
+			{
+				for (auto it = begin; it != end; ++it)
+				{
+					it->get();
+				}
+			}
+			else
+			{
+				std::vector<R> results;
+				results.reserve(std::distance(begin, end));
+				for (auto it = begin; it != end; ++it)
+				{
+					results.push_back(it->get());
+				}
+				return results;
+			}
+		});
+	}
+
 }