Lawrence Crowl wrote:

First, std::async and std::future have no flaws for what they were designed to do. They were designed to provide relatively easy parallelism for small core systems under the fork-join model.

I thought that it was well established by now that std::async isn't very useful for fork-join (if at all.) First, it's required to execute each (asynchronous) task as-if in a new thread with respect to thread locals, which in practice means "in a new thread". Second, it has to allocate the future shared state. These two non-flaws kill its performance for fork-join parallelism. The first one is not related to its use of std::future, but the second one is. Given an interface of the form X x; async_result<R> r; std::async( r, [&]{ return x.f(); } ); with async_result being non-copyable and non-movable and ~async_result blocking on the async task, the task can store its result directly into r, without needing to allocate.