std::promise::set_value_at_thread_exit

void set_value_at_thread_exit( const R& value );

void set_value_at_thread_exit( R&& value );

void set_value_at_thread_exit( R& value );

void 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 is atomic, i.e. it behaves as though they 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.

Parameters

Return value

(none).

Exceptions

std::future_error on the following conditions:

• *this has no shared state. The error category is set to no_state.
• The shared state already stores a value or exception. The error category is set to promise_already_satisfied.

Additionally:

Example

#include <iostream>
#include <future>
#include <thread>
 
using namespace std::literals::chrono_literals;
int main()
{
    std::promise<int> p;
    std::future<int> f = p.get_future();
    std::thread([p=std::move(p)]() mutable {
          std::this_thread::sleep_for(5s);
          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

See also