NAME

std::promise::set_value_at_thread_exit - std::promise::set_value_at_thread_exit

Synopsis

void set_value_at_thread_exit( const R& (member only of generic promise
value ); (1) template)
(since C++11)
(member only of generic promise
void set_value_at_thread_exit( R&& value ); (2) template)
(since C++11)
(member only of promise<R&> template
void set_value_at_thread_exit( R& value ); (3) specialization)
(since C++11)
(member only of promise<void>
void set_value_at_thread_exit() (4) template specialization)
(since C++11)

Stores the value into the shared state without making the state ready immediately.
The state is made ready when the current thread exits, after all variables with
thread-local storage duration have been destroyed.

The operation behaves as though set_value, set_exception, set_value_at_thread_exit,
and set_exception_at_thread_exit acquire a single mutex associated with the promise
object while updating the promise object.

An exception is thrown if there is no shared state or the shared state already
stores a value or exception.

Calls to this function do not introduce data races with calls to get_future
(therefore they need not synchronize with each other).

Parameters

value - value to store in the shared state

Return value

(none)

Exceptions

std::future_error on the following conditions:

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

* The shared state already stores a value or exception. The error code is set to
promise_already_satisfied.

Additionally:

1-2) Any exception thrown by the copy constructor of value
3) Any exception thrown by the move constructor of value

Example

// Run this code

#include <iostream>
#include <future>
#include <thread>

int main()
{
using namespace std::chrono_literals;
std::promise<int> p;
std::future<int> f = p.get_future();
std::thread([&p] {
std::this_thread::sleep_for(1s);
p.set_value_at_thread_exit(9);
}).detach();

std::cout << "Waiting..." << std::flush;
f.wait();
std::cout << "Done!\nResult is: " << f.get() << '\n';
}

Output:

Waiting...Done!
Result is: 9