异步std::async,std::future

C++标准库提供std::async ，std::future,两个高级接口。

async() ,使一个callable object，在后台运行成为一个独立线程。

class future<> ,允许等待线程结束获取其返回结果（返回值也可能是一个异常）。

#include 
   
    #include 
    
     #include 
     
      #include 
      
       #include 
       
        #include 
        
         #include 
         
          std::queue
          
            queue;std::mutex queueMutex;std::mutex cout;std::condition_variable queueCondVar;void provider(int value){ for(int i = 0; i < 10; ++i){ std::lock_guard
           
             lg(queueMutex); queue.push(value + i); } queueCondVar.notify_one(); //std::cout <
            
             <<" finish!"<< std::endl; std::this_thread::sleep_for(std::chrono::milliseconds(1000 * 100));}void consumer(int num){ while(true){ int va; { std::unique_lock
             
               ul(queueMutex); auto st = queueCondVar.wait_for(ul,std::chrono::seconds(2),[]{ return !queue.empty();}); if(queue.empty()){ //此时为false，说明了使用等待时间到了，而并非是返回值返回true std::cout <<"program stop or queue is empty!"<< std::endl; break; } //if(std::cv_status::no_timeout == st){ va = queue.front(); queue.pop(); //} } std::lock_guard
              
                l(cout); std::cout <<"consumer ID "<
               
                <<" : "<< va << std::endl; }}int main(){ auto p1 = std::async(std::launch::async,provider,1000); auto p2 = std::async(std::launch::async,provider,2000); auto p3 = std::async(std::launch::async,provider,1500); auto p4 = std::async(std::launch::async,provider,2500); auto c1 = std::async(std::launch::async,consumer,1); auto c2 = std::async(std::launch::async,consumer,2); auto c3 = std::async(std::launch::async,consumer,3); auto c4 = std::async(std::launch::async,consumer,4); auto c5 = std::async(std::launch::async,consumer,5); auto c6 = std::async(std::launch::async,consumer,6); auto c7 = std::async(std::launch::async,consumer,7);}