std::promise::get_future

 

C++

Language

Standard Library Headers

Freestanding and hosted implementations

Named requirements

Language support library

Concepts library (C++20)

Diagnostics library

Utilities library

Strings library

Containers library

Iterators library

Ranges library (C++20)

Algorithms library

Numerics library

Input/output library

Localizations library

Regular expressions library (C++11)

Atomic operations library (C++11)

Thread support library (C++11)

Filesystem library (C++17)

Technical Specifications

 

Thread support library

Threads
thread (C++11)
hardware_destructive_interference_sizehardware_constructive_interference_size (C++17)(C++17)
this_thread namespace
get_id (C++11) yield (C++11)	sleep_for (C++11) sleep_until (C++11)
Mutual exclusion
mutex (C++11) recursive_mutex (C++11) shared_mutex (C++17)	timed_mutex (C++11) recursive_timed_mutex (C++11) shared_timed_mutex (C++14)
Generic lock management
lock_guard (C++11) scoped_lock (C++17) unique_lock (C++11) shared_lock (C++14) defer_lock_ttry_to_lock_tadopt_lock_t (C++11)(C++11)(C++11)	lock (C++11) try_lock (C++11) defer_locktry_to_lockadopt_lock (C++11)(C++11)(C++11) once_flag (C++11) call_once (C++11)
Condition variables
condition_variable (C++11)
condition_variable_any (C++11)
notify_all_at_thread_exit (C++11)
cv_status (C++11)
Futures
promise (C++11) future (C++11) shared_future (C++11) packaged_task (C++11) async (C++11)	launch (C++11) future_status (C++11) future_error (C++11) future_category (C++11) future_errc (C++11)

 

std::promise

Member functions

promise::promise

promise::~promise

promise::operator=

promise::swap

Getting the result

promise::get_future

Setting the result

promise::set_value

promise::set_value_at_thread_exit

promise::set_exception

promise::set_exception_at_thread_exit

 

std::future<T> get_future();		(since C++11)

Returns a future object associated with the same shared state as *this.

An exception is thrown if *this has no shared state or get_future has already been called. To get multiple "pop" ends of the promise-future communication channel, use std::future::share.

Calls to this function do not introduce data races with calls to set_value, set_exception, set_value_at_thread_exit, or set_exception_at_thread_exit (but they need not synchronize with each other).

Parameters

(none)

Return value

A future referring to the shared state of *this

Exceptions

std::future_error on the following conditions:

• *this has no shared state. The error category is set to no_state.

• get_future() has already been called on a promise with the same shared state as *this. The error category is set to future_already_retrieved.