std::experimental::when_any

 

C++

Compiler support

Freestanding and hosted

Language

Standard library

Standard library headers

Named requirements

Feature test macros (C++20)

Language support library

Concepts library (C++20)

Metaprogramming library (C++11)

Diagnostics library

General utilities library

Strings library

Containers library

Iterators library

Ranges library (C++20)

Algorithms library

Numerics library

Localizations library

Input/output library

Filesystem library (C++17)

Regular expressions library (C++11)

Concurrency support library (C++11)

Technical specifications

Symbols index

External libraries

 

Technical specifications

Filesystem library (filesystem TS)

Library fundamentals (library fundamentals TS)

Library fundamentals 2 (library fundamentals TS v2)

Library fundamentals 3 (library fundamentals TS v3)

Extensions for parallelism (parallelism TS)

Extensions for parallelism 2 (parallelism TS v2)

Extensions for concurrency (concurrency TS)

Extensions for concurrency 2 (concurrency TS v2)

Concepts (concepts TS)

Ranges (ranges TS)

Reflection (reflection TS)

Mathematical special functions (special functions TR)

 

Extensions for concurrency

std::future extensions

experimental::future

experimental::shared_future

experimental::when_all

experimental::when_any

experimental::make_ready_future

experimental::make_exceptional_future

Latches and barriers

experimental::latch

experimental::barrier

experimental::flex_barrier

Atomic smart pointers

experimental::atomic_shared_ptr

experimental::atomic_weak_ptr

 

Defined in header <experimental/future>
template< class Sequence > struct when_any_result {     std::size_t index;     Sequence futures; };		(concurrency TS)
template< class InputIt > auto when_any( InputIt first, InputIt last )     -> future<when_any_result<std::vector<typename std::iterator_traits<InputIt>::value_type>>>;	(1)	(concurrency TS)
template< class... Futures > auto when_any( Futures&&... futures )     -> future<when_any_result<std::tuple<std::decay_t<Futures>...>>>;	(2)	(concurrency TS)

Create a future object that becomes ready when at least one 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 when_any_result<Sequence> and returns a future referring to the shared state. Every input future is moved into the corresponding object in the futures member of the when_any_result<Sequence> in the shared state, and every input shared_future is copied to the corresponding object in the futures member of the when_any_result<Sequence> in the shared state. The order of the objects in the Sequence matches the order of arguments.

1) This function does not participate in overload resolution unless InputIt's value type (i.e., typename std::iterator_traits<InputIt>::value_type) is a std::experimental::future or std::experimental::shared_future.

2) This function does not participate in overload resolution unless every argument is either a (possibly cv-qualified) std::experimental::shared_future or a cv-unqualified std::experimental::future. (Formally, for every type 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.

Return value

A future referring to the shared state created by the call. The future is always valid(), and it becomes ready when at least one of the input futures and shared_futures the call are ready. The index member of the when_any_result contains the position of the ready future or shared_future in the futures member.

1) If the range is empty (i.e., first == last), the returned future is ready immediately; the futures field of the when_any_result is an empty vector, and the index field is size_t(-1).

2) If no argument is provided, the returned future is ready immediately; the futures field of the when_any_result is an empty tuple, and the index field is size_t(-1).