std::promise<R>::~promise

~promise();

(since C++11)

Abandons the shared state:

if the shared state is ready, releases it.
if the shared state is not ready, stores an exception object of type std::future_error with an error condition std::future_errc::broken_promise, makes the shared state ready and releases it.

© cppreference.com
Licensed under the Creative Commons Attribution-ShareAlike Unported License v3.0.
http://en.cppreference.com/w/cpp/thread/promise/~promise