c++ 之 std::this_thread::yield 与std::this_thread::sleep_for

Myth丶恋晨 2022-04-13 15:07 337阅读 0赞

std::this\_thread::yield：　当前线程放弃执行，操作系统调度另一线程继续执行。即当前线程将未使用完的“CPU时间片”让给其他线程使用，等其他线程使用完后再与其他线程一起竞争"CPU"。  
std::this\_thread::sleep\_for：　表示当前线程休眠一段时间，休眠期间不与其他线程竞争CPU，根据线程需求，等待若干时间。

this\_thread 包装了一组可以访问当前线程信息的函数

1、get\_id()      获取当前线程的id。

// thread::get_id / this_thread::get_id
    #include <iostream>       // std::cout
    #include <thread>         // std::thread, std::thread::id, std::this_thread::get_id
    #include <chrono>         // std::chrono::seconds
     
    std::thread::id main_thread_id = std::this_thread::get_id();
     
    void is_main_thread() {
      if ( main_thread_id == std::this_thread::get_id() )
        std::cout << "This is the main thread.\n";
      else
        std::cout << "This is not the main thread.\n";
    }
     
    int main() 
    {
      is_main_thread();
      std::thread th (is_main_thread);
      th.join();
    }

输出结果

This is the main thread.
    This is not the main thread.

2、yield()  
调用线程放弃执行，回到准备状态，重新分配cpu资源。所以调用该方法后，可能执行其他线程，也可能还是执行该线程

// this_thread::yield example
    #include <iostream>       // std::cout
    #include <thread>         // std::thread, std::this_thread::yield
    #include <atomic>         // std::atomic
     
    std::atomic<bool> ready (false);
     
    void count1m(int id) {
      while (!ready) {             // wait until main() sets ready...
        std::this_thread::yield();
      }
      for (volatile int i=0; i<1000000; ++i) {}
      std::cout << id;
    }
     
    int main ()
    {
      std::thread threads[10];
      std::cout << "race of 10 threads that count to 1 million:\n";
      for (int i=0; i<10; ++i) threads[i]=std::thread(count1m,i);
      ready = true;               // go!
      for (auto& th : threads) th.join();
      std::cout << '\n';
     
      return 0;
    }

输出结果

race of 10 threads that count to 1 million...
    6189370542

3、template <class Clock, class Duration>  
       void sleep\_until (const chrono::time\_point<Clock,Duration>& abs\_time);  
阻塞调用线程，一直到指定事件

// this_thread::sleep_for example
    #include <iostream>       // std::cout
    #include <iomanip>        // std::put_time
    #include <thread>         // std::this_thread::sleep_until
    #include <chrono>         // std::chrono::system_clock
    #include <ctime>          // std::time_t, std::tm, std::localtime, std::mktime
     
    int main() 
    {
      using std::chrono::system_clock;
      std::time_t tt = system_clock::to_time_t (system_clock::now());
     
      struct std::tm * ptm = std::localtime(&tt);
      std::cout << "Current time: " << std::put_time(ptm,"%X") << '\n';
     
      std::cout << "Waiting for the next minute to begin...\n";
      ++ptm->tm_min; ptm->tm_sec=0;
      std::this_thread::sleep_until (system_clock::from_time_t (mktime(ptm)));
     
      std::cout << std::put_time(ptm,"%X") << " reached!\n";
     
      return 0;
    }

输出结果

Current time: 11:52:36
    Waiting for the next minute to begin...
    11:53:00 reached!

4、template <class Rep, class Period>  
       void sleep\_for (const chrono::duration<Rep,Period>& rel\_time);  
阻塞调用线程，一直到指定时间段后。

// this_thread::sleep_for example
    #include <iostream>       // std::cout
    #include <thread>         // std::this_thread::sleep_for
    #include <chrono>         // std::chrono::seconds
     
    int main() 
    {
      std::cout << "countdown:\n";
      for (int i=10; i>0; --i) {
        std::cout << i << '\n';
        std::this_thread::sleep_for (std::chrono::seconds(1));
      }
      std::cout << "Lift off!\n";
     
      return 0;
    }

输出结果

countdown:
    10
    9
    8
    7
    6
    5
    4
    3
    2
    1
    Lift off!

参考链接:

[https://en.cppreference.com/w/cpp/thread/sleep\_for][https_en.cppreference.com_w_cpp_thread_sleep_for]

[https://blog.csdn.net/u012085988/article/details/17225325][https_blog.csdn.net_u012085988_article_details_17225325]

[https://blog.csdn.net/Sandy\_WYM\_/article/details/83538635][https_blog.csdn.net_Sandy_WYM_article_details_83538635]

[https_en.cppreference.com_w_cpp_thread_sleep_for]: https://en.cppreference.com/w/cpp/thread/sleep_for
[https_blog.csdn.net_u012085988_article_details_17225325]: https://blog.csdn.net/u012085988/article/details/17225325
[https_blog.csdn.net_Sandy_WYM_article_details_83538635]: https://blog.csdn.net/Sandy_WYM_/article/details/83538635