Std::future::wait_until (3) Linux Manual Page

std::future<T>::wait_until – std::future<T>::wait_until

Synopsis

template <class Clock, class Duration>
(since C++ 11)

    std::future_status wait_until(const std::chrono::time_point<Clock, Duration> &timeout_time) const;

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.

Parameters

timeout_time – maximum time point to block until

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

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)

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.

Example

// Run this code

#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) {
        std::this_thread::sleep_for(std::chrono::seconds(1));
        p1.set_value_at_thread_exit(9);
    },
                std::move(p1))
        .detach();
    // 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::this_thread::sleep_for(std::chrono::seconds(5));
        p2.set_value_at_thread_exit(8);
    },
                std::move(p2))
        .detach();
    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";
    } else {
        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";
    } else {
        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!
  Done!

std::future::wait_until (3) Linux Manual Page