std::promise<R>::set_value_at_thread_exit
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std::promise
Member functions
Getting the result
Setting the result
promise::set_value_at_thread_exit
Non-member Functions
Helper Classes
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).
[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() { 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
[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 indicate an exception while delivering the notification only at thread exit
(public member function) [edit]
(public member function) [edit]