std::experimental::when_all
| Defined in header <experimental/future>
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| template < class InputIt > auto when_all(InputIt first, InputIt last) |
(1) | (concurrency TS) |
| template < class... Futures > auto when_all(Futures&&... futures) |
(2) | (concurrency TS) |
Create a future object that becomes ready when all of the input futures and shared_futures become ready. The behavior is undefined if any input future or shared_future is invalid.
In particular, let Sequence be a std::vector<typename std::iterator_traits<InputIt>::value_type> for (1) and std::tuple<std::decay_t<Futures>...> for (2). This function template creates a shared state containing Sequence and returns a future referring to the shared state. Every input future is moved into the corresponding object in the Sequence in the shared state, and every input shared_future is copied to the corresponding object in the Sequence in the shared state. The order of the objects in the Sequence matches the order of arguments.
InputIt's value type (i.e., typename std::iterator_traits<InputIt>::value_type) is a std::experimental::future or std::experimental::shared_future.Fn in Futures, either std::remove_reference_t<Fn> is std::experimental::future<Rn>, or std::decay_t<Fn> is std::experimental::shared_future<Rn>.)After this call, every input future is no longer valid; every input shared_future remains valid.
[edit] Return value
A future referring to the shared state created by the call. The future is always valid(), and it becomes ready when all of the input futures and shared_futures the call are ready.
future contains an empty vector and is ready immediately.future<std::tuple<>> is returned and is immediately ready.