Drogon C++ 如何在不阻塞的情况下等待未来？

Question

I just learn about Drogon C++ framework, in many places it uses callback for async tasks. It is like a javascript callback long time ago. Javascript now has future.then and also the async await .

So my question is it possible using future->then for wait the result to be ready. From what I read the std::future does not have .then method . Maybe any other library that able to achieve it?

Using current callback especially for database access (query to database) are so nested.

Answer 1

other frameworks like Qt used additional shared states to identify state of original state's owner (eg finished , running , etc.). C++ standard component library introduces a value of std::future_status returned by wait_for(const chrono::duration<Rep,Period>& rel_time) .

If the shared state is not yet ready, the function blocks the calling thread and waits until it is ready or until rel_time has elapsed, whichever happens first.

You can set zero timeout and determine if future is ready or not.

I'm afraid that call-back feature should be implemented as part of query, eg to make function-wrapper which would accept pointer to a callback function and call it when task is finished (a future in this case is superfluos, callback would be called in context of asynchronous thread).