C++ Coroutines Advanced: Converting std:future to asio:awaitable

Summary

In modern C++ development, coroutines have brought revolutionary changes to asynchronous programming. However, when using boost::asio or standalone asio, we often encounter scenarios where we need to convert traditional std::future<T> to asio::awaitable<T>. This article will detail an efficient, thread-safe conversion method.Problem BackgroundWhen using asio coroutines, we often encounter scenarios like:Need to call third-party libraries that return std::future (such as database drivers)Want to use co_await in coroutines to handle these asynchronous operationsDon’t want to block IO threads, maintaining high performanceTraditional solutions might use timer polling or directly call future.get() in IO threads, but these methods are either inefficient or block IO threads.Core SolutionOur solution is based on asio::async_initiate, which provides perfect integration with the asio coroutine system while avoiding the problem of blocking IO threads.Core Implementation#include <asio.hpp> #include <future> #include <optional> #include <tuple> // Thread pool for handling blocking operations asio::thread_pool blocking_pool(4); // Convert std::future<T> to asio::awaitable<T> template<typename T, typename CompletionToken> auto future_to_awaitable(std::future<T> future, CompletionToken&& token) { return asio::async_initiate<CompletionToken, void(std::tuple<std::optional<T>, std::exception_ptr>)>( [future = std::move(future)](auto&& handler) mutable { auto executor = asio::get_associated_executor(handler); // Execute blocking operation in thread pool to avoid blocking IO thread asio::post(blocking_pool, [future = std::move(future), handler = std::move(handler), executor]() mutable { std::tuple<std::optional<T>, std::exception_ptr> result; try { T value = future.get(); result = std::make_tuple(std::make_optional(std::move(value)), nullptr); } catch (...) { result = std::make_tuple(std::nullopt, std::current_exception()); } // Return to original executor context to call handler asio::...