std::promise<R>::set_value_at_thread_exit
From cppreference.com
Main template | ||
void set_value_at_thread_exit(const R& value ); | (1) | (since C++11) |
void set_value_at_thread_exit( R&& value ); | (2) | (since C++11) |
std::promise<R&> specializations | ||
void set_value_at_thread_exit( R& value ); | (3) | (since C++11) |
std::promise<void> specialization | ||
void set_value_at_thread_exit(); | (4) | (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.
Calls to this function do not introduce data races with calls to get_future (therefore they need not synchronize with each other).
Contents |
[edit]Parameters
| value | - | value to store in the shared state |
[edit]Return value
(none)
[edit]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) Any exception thrown by the constructor selected to copy an object of type
R.2) Any exception thrown by the constructor selected to move an object of type
R.[edit]Example
Run this code
#include <future>#include <iostream>#include <thread> int main(){usingnamespace 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
[edit]Defect reports
The following behavior-changing defect reports were applied retroactively to previously published C++ standards.
| DR | Applied to | Behavior as published | Correct behavior |
|---|---|---|---|
| LWG 2098 | C++11 | it was unclear which exceptions are required to be thrown | made clear |
[edit]See also
| sets the result to specific value (public member function) | |
| sets the result to indicate an exception while delivering the notification only at thread exit (public member function) |
