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????????????futures

??????????????????????????????????????????????????????????C++???????Condition Variables??futures???????????????????????

1. ?????????

????????????????????????????????????????????????????????????????????????

???????

?????????C++???std::this_thread::sleep_for()?????????????????????????????????????????????????????????????????

???????

???????????????????????????std::mutex???????????????????????C++???????????

• std::condition_variable
• std::condition_variable_any

??????std::mutex?????????????std::mutex???????

2. ??futures???????

std::future?std::shared_future?C++???????????????

futures?????

std::future????????????????????????std::shared_future????std::future?????????????????????????

???????

C++???std::async()????????????std::async()????std::thread??????????????????std::function???

?????std::packaged_task

std::packaged_task???????????????????std::future????????????std::function??????????????????????

3. ??????????

???????????????????????????futures???????????????????

???????

??????????????futures????????????????????????????

template
   
    std::list
    
      parallel_quick_sort(std::list
     
       input) {    if (input.empty()) return input;    t pivot = input.front();    auto divide_point = std::partition(input.begin(), input.end(),        [&pivot](t const& t) { return t < pivot; });    std::future
      
       
        > new_lower = std::async(parallel_quick_sort, input.begin(),         input.end(), divide_point);    std::future
        
         
          > new_higher = std::async(parallel_quick_sort, input.begin(), input.end()); return std::move(new_lower.get()) + new_higher.get();}
         
        
       
      
     
    
   

???????

????futures?????????????????????????????

template
   
    std::future
    
     
      > spawn_task(func f, a&& a) {    typedef std::result_of
      
       ::type result_type;    std::packaged_task
       
        
         ::type(a&&)> task(f); std::future
         
           res = task.get_future(); std::thread t(std::move(task), std::move(a)); t.detach(); return res;}
         
        
       
      
     
    
   

4. ??????

?????????????????????????C++???std::chrono?????????????

??????

• std::chrono::time_point??????????
• std::chrono::steady_clock????????????????????

??

std::condition_variable cv;std::mutex m;bool done = false;auto timeout = std::chrono::steady_clock::now() + std::chrono::milliseconds(500);std::unique_lock
   
     lk(m);while (!done) {    auto result = cv.wait_until(lk, timeout);    if (result == std::cv_status::timeout) {        break;    }}
   

??

?????????futures????????????????????????????????????????????????????????