The class template std::future provides a mechanism to access the result of asynchronous operations: An asynchronous operation (performed via std::async, std::packaged_task, or std::promise) can …

Blocks until the result becomes available. valid() == true after the call. The behavior is undefined if valid () == false before the call to this function.

The return type of std::async is std::future<V>, where V is: ... The call to std::async synchronizes with the call to f, and the completion of f is sequenced before making the shared state ready.

If the future is the result of a call to std::async that used lazy evaluation, this function returns immediately without waiting. This function may block for longer than timeout_duration due to scheduling or …

namespace std { template<class R> class shared_future { public: shared_future() noexcept; shared_future(const shared_future& rhs) noexcept; shared_future(future<R>&&) noexcept; …

Checks if the future refers to a shared state. This is the case only for futures that were not default-constructed or moved from (i.e. returned by std::promise::get_future (), …

The promise is the "push" end of the promise-future communication channel: the operation that stores a value in the shared state synchronizes-with (as defined in std::memory_order) the successful return …

Dec 28, 2021 · In summary: std::future is an object used in multithreaded programming to receive data or an exception from a different thread; it is one end of a single-use, one-way communication …

The get member function waits (by calling wait ()) until the shared state is ready, then retrieves the value stored in the shared state (if any). Right after calling this function, valid () is false. If valid () is false …

Transfers the shared state of *this, if any, to a std::shared_future object. Multiple std::shared_future objects may reference the same shared state, which is not possible with std::future. After calling …