std::future<T>::wait

 

C++

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Threads thread (C++11) jthread (C++20) stop_token (C++20) stop_source (C++20) stop_callback (C++20) hardware_destructive_interference_sizehardware_constructive_interference_size (C++17)(C++17)     this_thread namespace get_id (C++11) yield (C++11) sleep_for (C++11) sleep_until (C++11) Atomic types atomic (C++11) atomic_ref (C++20) atomic_flag (C++11) Initialization of atomic types atomic_init (C++11)(deprecated in C++20) ATOMIC_VAR_INIT (C++11)(deprecated in C++20) ATOMIC_FLAG_INIT (C++11) Free functions for atomic operations atomic_storeatomic_store_explicit (C++11)(C++11) atomic_loadatomic_load_explicit (C++11)(C++11) atomic_exchangeatomic_exchange_explicit (C++11)(C++11) atomic_compare_exchange_weakatomic_compare_exchange_weak_explicitatomic_compare_exchange_strongatomic_compare_exchange_strong_explicit (C++11)(C++11)(C++11)(C++11) atomic_fetch_addatomic_fetch_add_explicit (C++11)(C++11) atomic_fetch_subatomic_fetch_sub_explicit (C++11)(C++11) atomic_fetch_andatomic_fetch_and_explicit (C++11)(C++11) atomic_fetch_oratomic_fetch_or_explicit (C++11)(C++11) atomic_fetch_xoratomic_fetch_xor_explicit (C++11)(C++11) atomic_is_lock_free (C++11) atomic_waitatomic_wait_explicit (C++20)(C++20) atomic_notify_one (C++20) atomic_notify_all (C++20)

Free functions for atomic flags atomic_flag_test_and_setatomic_flag_test_and_set_explicit (C++11)(C++11) atomic_flag_clearatomic_flag_clear_explicit (C++11)(C++11) atomic_flag_testatomic_flag_test_explicit (C++20)(C++20) atomic_flag_waitatomic_flag_wait_explicit (C++20)(C++20) atomic_flag_notify_one (C++20) atomic_flag_notify_all (C++20) Memory ordering memory_order (C++11) kill_dependency (C++11) atomic_thread_fence (C++11) atomic_signal_fence (C++11) Mutual exclusion mutex (C++11) recursive_mutex (C++11) shared_mutex (C++17) timed_mutex (C++11) recursive_timed_mutex (C++11) shared_timed_mutex (C++14) Generic lock management lock_guard (C++11) scoped_lock (C++17) unique_lock (C++11) shared_lock (C++14) defer_lock_ttry_to_lock_tadopt_lock_t (C++11)(C++11)(C++11) lock (C++11) try_lock (C++11) defer_locktry_to_lockadopt_lock (C++11)(C++11)(C++11) once_flag (C++11) call_once (C++11) Condition variables condition_variable (C++11) condition_variable_any (C++11) notify_all_at_thread_exit (C++11) cv_status (C++11) Semaphores counting_semaphorebinary_semaphore (C++20)(C++20) Latches and barriers latch (C++20) barrier (C++20) Futures promise (C++11) future (C++11) shared_future (C++11) packaged_task (C++11) async (C++11) launch (C++11) future_status (C++11) future_error (C++11) future_category (C++11) future_errc (C++11)

 

std::future

Member functions

future::future

future::~future

future::operator=

future::share

Getting the result

future::get

State

future::valid

future::wait

future::wait_for

future::wait_until

 

void wait() const;		(since C++11)

Blocks until the result becomes available. valid() == true after the call.

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

Parameters

(none)

Return value

(none)

Exceptions

May throw implementation-defined exceptions.

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 <chrono>
#include <iostream>
#include <future>
#include <thread>
 
int fib(int n)
{
  if (n < 3) return 1;
  else return fib(n-1) + fib(n-2);
}
 
int main()
{
    std::future<int> f1 = std::async(std::launch::async, [](){
        return fib(40);
    });
    std::future<int> f2 = std::async(std::launch::async, [](){
        return fib(43);
    });
 
    std::cout << "waiting... " << std::flush;
    const auto start = std::chrono::system_clock::now();
 
    f1.wait();
    f2.wait();
 
    const auto diff = std::chrono::system_clock::now() - start;
    std::cout << std::chrono::duration<double>(diff).count() << " seconds\n";
 
    std::cout << "f1: " << f1.get() << '\n';
    std::cout << "f2: " << f2.get() << '\n';
}

Possible output:

waiting... 1.61803 seconds
f1: 102334155
f2: 433494437

See also

wait_for	waits for the result, returns if it is not available for the specified timeout duration (public member function)
wait_until	waits for the result, returns if it is not available until specified time point has been reached (public member function)