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std::shared...e::wait_for(3) C++ Standard Libary std::shared...e::wait_for(3) NAME std::shared_future::wait_for - std::shared_future::wait_for Synopsis template< class Rep, class Period > std::future_status wait_for( const std::chrono::duration<Rep,Pe- riod>& (since C++11) timeout_duration ) const; Waits for the result to become available. Blocks until specified timeout_duration has elapsed or the result becomes available, whichever comes first. The return value identifies the state of the result. If the future is the result of a call to std::async that used lazy evaluation, this function returns immediately without waiting. This function may block for longer than timeout_duration due to scheduling or resource contention delays. The standard recommends that a steady clock is used to measure the duration. If an implementation uses a system clock instead, the wait time may also be sensitive to clock adjustments. The behavior is undefined if valid() is false before the call to this function. Parameters timeout_duration - maximum duration to block for Return value Constant Explanation The shared state contains a deferred func- tion using lazy future_status::deferred evaluation, so the result will be computed only when explicitly requested 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 std::future_error with an error condition of std::future_errc::no_state. Example // Run this code #include <iostream> #include <future> #include <thread> #include <chrono> using namespace std::chrono_literals; int main() { std::shared_future<int> future = std::async(std::launch::async, [](){ std::this_thread::sleep_for(3s); return 8; }); std::cout << "waiting...\n"; std::future_status status; do { switch(status = future.wait_for(1s); status) { case std::future_status::deferred: std::cout << "de- ferred\n"; break; case std::future_status::timeout: std::cout << "time- out\n"; break; case std::future_status::ready: std::cout << "ready!\n"; break; } } while (status != std::future_status::ready); std::cout << "result is " << future.get() << '\n'; } Possible output: waiting... timeout timeout timeout ready! result is 8 See also wait waits for the result to become available (public member function) waits for the result, returns if it is not available un- til specified time wait_until point has been reached (public member function) http://cppreference.com 2022.07.31 std::shared...e::wait_for(3)
NAME | Synopsis | Parameters | Return value | Exceptions | Notes | Example | Possible output: | See also
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