C++多线程编程第十讲--future其他成员函数、shared_future、atomic

//(1)std::future的其他成员函数

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#include<iostream> #include<mutex> #include<thread> #include<future>   using namespace std;   int my_thread() {     cout << "my_thread start...  " << "thread id = " << this_thread::get_id() << endl;     std::chrono::milliseconds duro(5000);     std::this_thread::sleep_for(duro);     cout << "my_thread end...  " << "thread id = " << this_thread::get_id() << endl;     return 5; }   int main() {     cout << "main() start... " << "thread id = " << std::this_thread::get_id() << endl;     std::future<int> result = std::async(my_thread);     std::future_status status = result.wait_for(std::chrono::milliseconds(6000));  //等待     if (status == std::future_status::timeout)     {         //超时表示等待的线程还没有执行结束         cout << "overtime..." << endl;     }     else if (status == std::future_status::ready)     {         cout << "ready..." << endl;     }     else if (status == std::future_status::deferred)  //线程还没开始执行     {         cout << "deferred..." << endl;           //对应async中第一个参数中的std::launch::deferred     }       cout << result.get() << endl;              //主线程会在get这里一致等到新的线程返回结果     cout << "main() end... " << "thread id = " << std::this_thread::get_id() << endl;     return 0; }   //(2)std::shared_future // 是一个类模板，他的get函数就不是转移了，而是复制。 // // 如以下程序，只能在线程2中调用get，如果还有其他线程想要线程1返回的结果再次调用get的时候 // 程序就会报错 #include<iostream> #include<mutex> #include<thread> #include<future>   using namespace std;   int my_thread(int mypar) {     cout << "my_thread start...  " << "thread id = " << this_thread::get_id() << endl;     std::chrono::milliseconds duro(5000);     std::this_thread::sleep_for(duro);     cout << "my_thread end...  " << "thread id = " << this_thread::get_id() << endl;     return mypar; }   void my_thread2(std::future<int>& fut) {     cout << "my_thread2 start..." << "thread id = " << this_thread::get_id() << endl;     //程序运行到这里，即便线程1还没有执行结束，调用get也会等待线程1返回结果再运行     cout << "fut.get() = " << fut.get() << endl;  //打印返回的结果，get函数设计是一个移动语义,所以不能调用两次。     cout << "my_thread2 end..." << "thread id = " << this_thread::get_id() << endl; }   int main() {     cout << "main() start... " << "thread id = " << std::this_thread::get_id() << endl;       std::packaged_task<int(int)> mypt(my_thread);           //把函数my_thread包装起来     std::thread t1(std::ref(mypt), 5);                      //用一个package_task对象作为线程的参数       std::future<int> result = mypt.get_future();       //std::shared_future<int> s_fut(std::move(result));    //使用右值         std::thread t2(my_thread2, std::ref(result));     //future对象不能拷贝，所以只能以std::ref的方式进行传递     t2.join();     t1.join();     cout << "main() end... " << "thread id = " << std::this_thread::get_id() << endl;     return 0; }   // 则使用shared_future避免以上的情况   #include<iostream> #include<mutex> #include<thread> #include<future>   using namespace std;   int my_thread(int mypar) {     cout << "my_thread start...  " << "thread id = " << this_thread::get_id() << endl;     std::chrono::milliseconds duro(5000);     std::this_thread::sleep_for(duro);     cout << "my_thread end...  " << "thread id = " << this_thread::get_id() << endl;     return mypar; }   void my_thread2(std::shared_future<int>& s_fut) {     cout << "my_thread2 start..." << "thread id = " << this_thread::get_id() << endl;     //程序运行到这里，即便线程1还没有执行结束，调用get也会等待线程1返回结果再运行     cout << "fut.get() = " << s_fut.get() << endl;  //get只是复制，可以调用多次     cout << "my_thread2 end..." << "thread id = " << this_thread::get_id() << endl; }   void my_thread3(std::shared_future<int>& s_fut) {     cout << "my_thread3 start..." << "thread id = " << this_thread::get_id() << endl;     //程序运行到这里，即便线程1还没有执行结束，调用get也会等待线程1返回结果再运行     cout << "fut.get() = " << s_fut.get() << endl;  //get只是复制，可以调用多次     cout << "my_thread3 end..." << "thread id = " << this_thread::get_id() << endl; }   int main() {     cout << "main() start... " << "thread id = " << std::this_thread::get_id() << endl;       std::packaged_task<int(int)> mypt(my_thread);           //把函数my_thread包装起来     std::thread t1(std::ref(mypt), 5);                      //用一个package_task对象作为线程的参数       std::future<int> result = mypt.get_future();       //bool value = result.valid();  //可以用来判断result中是否有有效值       std::shared_future<int> s_fut(std::move(result));    //使用右值     //std::shared_future<int> s_fut(result.share());    //使用右值,两种写法都可以       std::thread t2(my_thread2, std::ref(s_fut));     //future对象不能拷贝，所以只能以std::ref的方式进行传递     std::thread t3(my_thread3, std::ref(s_fut));     //future对象不能拷贝，所以只能以std::ref的方式进行传递     t2.join();     t1.join();     t3.join();     cout << "main() end... " << "thread id = " << std::this_thread::get_id() << endl;     return 0; }   #include<iostream> #include<mutex> #include<thread> #include<future>   using namespace std;   int my_thread(int mypar) {     cout << "my_thread start...  " << "thread id = " << this_thread::get_id() << endl;     std::chrono::milliseconds duro(5000);     std::this_thread::sleep_for(duro);     cout << "my_thread end...  " << "thread id = " << this_thread::get_id() << endl;     return mypar; }   void my_thread2(std::shared_future<int>& s_fut) {     cout << "my_thread2 start..." << "thread id = " << this_thread::get_id() << endl;     //程序运行到这里，即便线程1还没有执行结束，调用get也会等待线程1返回结果再运行     cout << "fut.get() = " << s_fut.get() << endl;  //get只是复制，可以调用多次     cout << "my_thread2 end..." << "thread id = " << this_thread::get_id() << endl; }   void my_thread3(std::shared_future<int>& s_fut) {     cout << "my_thread3 start..." << "thread id = " << this_thread::get_id() << endl;     //程序运行到这里，即便线程1还没有执行结束，调用get也会等待线程1返回结果再运行     cout << "fut.get() = " << s_fut.get() << endl;  //get只是复制，可以调用多次     cout << "my_thread3 end..." << "thread id = " << this_thread::get_id() << endl; }   int main() {     cout << "main() start... " << "thread id = " << std::this_thread::get_id() << endl;       std::packaged_task<int(int)> mypt(my_thread);           //把函数my_thread包装起来     std::thread t1(std::ref(mypt), 5);                      //用一个package_task对象作为线程的参数       //bool value = result.valid();  //可以用来判断result中是否有有效值       std::shared_future<int> s_fut(mypt.get_future());    //使用右值     //std::shared_future<int> s_fut(result.share());    //使用右值,两种写法都可以       std::thread t2(my_thread2, std::ref(s_fut));     //future对象不能拷贝，所以只能以std::ref的方式进行传递     std::thread t3(my_thread3, std::ref(s_fut));     //future对象不能拷贝，所以只能以std::ref的方式进行传递     t2.join();     t1.join();     t3.join();     cout << "main() end... " << "thread id = " << std::this_thread::get_id() << endl;     return 0; }   //(3)原子操作std::atomic     //(3.1)原子操作概念引出范例    #include<iostream> #include<mutex> #include<thread> #include<future>   using namespace std;   int g_mycount = 0; mutex g_my_mutex;   void my_thread() {     int i = 0;     for (; i < 1000000; ++i)     {         g_my_mutex.lock();          //防止++的执行被打断         g_mycount++;         g_my_mutex.unlock();     } }     int main() {     cout << "main() start... " << "thread id = " << std::this_thread::get_id() << endl;       thread mythread(my_thread);       thread mythread2(my_thread);       mythread.join();     mythread2.join();         cout << g_mycount << endl;      cout << "main() end... " << "thread id = " << std::this_thread::get_id() << endl;     return 0; }   // 但是以上的程序效率太低，原子操作也会有相同的作用。互斥量的加锁针对的是一个代码段，而原子操作 // 针对的是一个变量。原子操作用于统计功能等。   //(3.2)基本的std::atomic用法范例   #include<iostream>     #include<mutex>     #include<thread>     #include<future>           using namespace std;                 //int g_mycount = 0;     std::atomic<int> g_mycount = 0;   //具备原子操作的整型值           void my_thread()     {         int i = 0;         for (; i < 1000000; ++i)         {             g_mycount++;         }     }                 int main()     {         cout << "main() start... " << "thread id = " << std::this_thread::get_id() << endl;               thread mythread(my_thread);               thread mythread2(my_thread);               mythread.join();         mythread2.join();               cout << g_mycount << endl;         cout << "main() end... " << "thread id = " << std::this_thread::get_id() << endl;         return 0;     }                    #include<iostream>     #include<mutex>     #include<thread>     #include<future>           using namespace std;                 //int g_mycount = 0;     std::atomic<bool> g_ifend = false;           void my_thread()     {         std::chrono::milliseconds dura(1000); //               while (g_ifend == false)         {             cout << "my_thread id = " << std::this_thread::get_id() << endl;             std::this_thread::sleep_for(dura);         }     }           int main()     {         cout << "main() start... " << "thread id = " << std::this_thread::get_id() << endl;               thread mythread(my_thread);               thread mythread2(my_thread);               std::chrono::milliseconds dura(5000); //         std::this_thread::sleep_for(dura);               g_ifend = true;               mythread.join();         mythread2.join();               cout << "main() end... " << "thread id = " << std::this_thread::get_id() << endl;         return 0;     }