< cpp‎ | thread‎ | future
Thread support library
this_thread namespace
Mutual exclusion
Generic lock management
Condition variables
template< class Clock, class Duration >
std::future_status wait_until( const std::chrono::time_point<Clock,Duration>& timeout_time ) const;
(since C++11)

wait_until waits for a result to become available. It blocks until specified timeout_time has been reached or the result becomes available, whichever comes first. The return value indicates why wait_until returned.

The behavior is undefined if valid()== false before the call to this function.


[edit] Parameters

timeout_time - maximum time point to block until

[edit] Return value

Constant Explanation
future_status::deferred The function to calculate the result has not been started yet
future_status::ready The result is ready
future_status::timeout The timeout has expired

[edit] Exceptions

Any exception thrown by clock, time_point, or duration during the execution (clocks, time points, and durations provided by the standard library never throw)

[edit] Notes

The implementations are encouraged to detect the case when valid == false before the call and throw a future_error with an error condition of future_errc::no_state.

The clock tied to timeout_time is used, which is not required to be a monotonic clock.There are no guarantees regarding the behavior of this function if the clock is adjusted discontinuously, but the existing implementations convert timeout_time from Clock to std::chrono::system_clock and delegate to POSIX pthread_cond_timedwait so that the wait honors ajustments to the system clock, but not to the the user-provided Clock. In any case, the function also may wait for longer than until after timeout_time has been reached due to scheduling or resource contention delays.

[edit] Example

#include <iostream>
#include <future>
#include <thread>
#include <chrono>
int main()
    std::chrono::system_clock::time_point two_seconds_passed
        = std::chrono::system_clock::now() + std::chrono::seconds(2);
    // Make a future that that takes 1 second to completed
    std::promise<int> p1;
    std::future<int> f_completes = p1.get_future();
    std::thread([](std::promise<int> p1)
    // Make a future that that takes 5 seconds to completed
    std::promise<int> p2;
    std::future<int> f_times_out = p2.get_future();
    std::thread([](std::promise<int> p2)
    std::cout << "Waiting for 2 seconds..." << std::endl;
    if(std::future_status::ready == f_completes.wait_until(two_seconds_passed))
        { std::cout << "f_completes: " << f_completes.get() << "\n"; }
        { std::cout << "f_completes did not complete!\n"; }
    if(std::future_status::ready == f_times_out.wait_until(two_seconds_passed))
        { std::cout << "f_times_out: " << f_times_out.get() << "\n"; }
        { std::cout << "f_times_out did not complete!\n"; }
    std::cout << "Done!\n";

Possible output:

Waiting for 2 seconds...
f_completes: 9
f_times_out did not complete!

[edit] See also

waits for the result to become available
(public member function) [edit]
waits for the result, returns if it is not available for the specified timeout duration
(public member function) [edit]