std::promise<R>:: set_value_at_thread_exit

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.

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

Parameters

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:

Example

#include <future>
#include <iostream>
#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';
}

Waiting... Done!
Result is: 9

Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

See also