std::shared_future
Defined in header <future> | ? | ? |
|---|---|---|
template< class T > class shared_future; | (1) | (since C++11) |
template< class T > class shared_future<T&>; | (2) | (since C++11) |
template<> class shared_future<void>; | (3) | (since C++11) |
类模板std::shared_future提供访问异步操作结果的机制，类似于std::future，只是允许多个线程等待相同的共享状态。不像std::future，因此只有一个实例可以引用任何特定的异步结果%29，std::shared_future是可复制的，多个共享的未来对象可能引用相同的共享状态。
如果每个线程通过自己的副本访问同一个共享状态，则从多个线程访问该状态是安全的。shared_future对象。
成员函数
(constructor) | constructs the future object (public member function) |
|---|---|
(destructor) | destructs the future object (public member function) |
operator= | assigns the contents (public member function) |
得到结果
GET返回结果%28公共成员函数%29
国家
有效检查未来是否具有共享状态%28公共成员函数%29
等待结果变为可用%28公共成员函数%29
等待[医]对于等待结果，如果指定的超时持续时间%28公共成员函数%29不可用，则返回
等待[医]在等待结果之前，如果指定的时间点已达到%28公共成员函数%29，则返回不可用的结果。
例
阿shared_future可用于同时向多个线程发送信号，类似于std::condition_variable::notify_all()...
二次
#include <iostream>
#include <future>
#include <chrono>
int main()
{
std::promise<void> ready_promise, t1_ready_promise, t2_ready_promise;
std::shared_future<void> ready_future(ready_promise.get_future());
std::chrono::time_point<std::chrono::high_resolution_clock> start;
auto fun1 = [&, ready_future]() -> std::chrono::duration<double, std::milli>
{
t1_ready_promise.set_value();
ready_future.wait(); // waits for the signal from main()
return std::chrono::high_resolution_clock::now() - start;
};
auto fun2 = [&, ready_future]() -> std::chrono::duration<double, std::milli>
{
t2_ready_promise.set_value();
ready_future.wait(); // waits for the signal from main()
return std::chrono::high_resolution_clock::now() - start;
};
auto result1 = std::async(std::launch::async, fun1);
auto result2 = std::async(std::launch::async, fun2);
// wait for the threads to become ready
t1_ready_promise.get_future().wait();
t2_ready_promise.get_future().wait();
// the threads are ready, start the clock
start = std::chrono::high_resolution_clock::now();
// signal the threads to go
ready_promise.set_value();
std::cout << "Thread 1 received the signal "
<< result1.get().count() << " ms after start\n"
<< "Thread 2 received the signal "
<< result2.get().count() << " ms after start\n";
}二次
可能的产出：
二次
Thread 1 received the signal 0.072 ms after start
Thread 2 received the signal 0.041 ms after start二次
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