std::future::future - cppreference.com ([original](https://en.cppreference.com/w/cpp/thread/future/future.html)) (raw)

Releases any shared state. This means:

These actions will not block for the shared state to become ready, except that they may block if all following conditions are satisfied: The shared state was created by a call to std::async. The shared state is not yet ready. The current object was the last reference to the shared state. (since C++14)