std::future::wait

 

C++

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Thread support library

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thread (C++11)
this_thread namespace
get_id (C++11) yield (C++11)	sleep_for (C++11) sleep_until (C++11)
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mutex (C++11) timed_mutex (C++11)	recursive_mutex (C++11) recursive_timed_mutex (C++11)
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lock_guard (C++11) unique_lock (C++11) defer_lock_t try_to_lock_t adopt_lock_t (C++11) (C++11) (C++11)	lock (C++11) try_lock (C++11) defer_lock try_to_lock adopt_lock (C++11) (C++11) (C++11)
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std::future

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;

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

(none)

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.

Example

run this code

#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(20);
    });
    std::future<int> f2 = std::async(std::launch::async, [](){
        return fib(25);
    });                                                                                                                                                                                                     
 
    std::cout << "waiting...\n";
    f1.wait();
    f2.wait();
 
    std::cout << "f1: " << f1.get() << '\n';
    std::cout << "f2: " << f2.get() << '\n';
}

Output:

waiting...
f1: 6765
f2: 75025

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)