C++ async

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考慮如下代碼：

#include <iostream>#include <string>#include <thread>#include <mutex>#include <condition_variable> std::mutex m;std::condition_variable cv;std::string data;bool ready = false;int result =0; void do_work(){    std::this_thread::sleep_for(std::chrono::seconds(1));    result = 123;    {        std::lock_guard<std::mutex> lk(m);        ready = true;    }    cv.notify_one();} int main(){    std::thread thread(do_work);    thread.detach();        std::unique_lock<std::mutex> lk(m);    cv.wait(lk, []{return ready;});    std::cout << "result=" << result << ‘\n‘;}

C++11引入了promise和future，可以使用task-based思維

#include <iostream>#include <cstdlib>#include <future>#include <chrono>void do_work(std::promise<int> promise){    std::this_thread::sleep_for(std::chrono::seconds(1));    promise.set_value(123);}int main(){      std::promise<int> promise;    std::future<int> future = promise.get_future();    std::thread thread( do_work , std::move(promise));    thread.detach();    future.wait();    std::cout << "result=" << future.get() << ‘\n‘;}

看看，是不是精簡了很多代碼？現在繼續精簡，用std::async代碼如下：

#include <iostream>#include <cstdlib>#include <future>#include <chrono>int main(){      std::future<int> future = std::async( [](){ std::this_thread::sleep_for(std::chrono::seconds(1));                                                return 123; });    future.wait();    std::cout << "result is " << future.get() << ‘\n‘;}

另外，介紹個C++線上編譯器 https://wandbox.org/

C++ async