体验智能指针的强大5

智能指针5

• 多线程访问共享对象的安全问题

  #include <chrono>
  # include <iostream>
  # include <memory>
  # include <thread>
  
  class A{
  public:
      A() {
          std::cout << "A()" << std::endl;
      }
  
      ~A() {
          std::cout << "~A()" << std::endl;
      }
  
      void func() {
          std::cout << "do sth" << std::endl;
      }
  };
  
  void handler(std::weak_ptr<A> wp)
  {
      std::this_thread::sleep_for(std::chrono::seconds(2));
      std::shared_ptr<A> sp = wp.lock();
      if (sp) {
          sp->func();
      } else {
          std::cout << "not callable" << std::endl;
      }
  }
  
  int main()
  {
      {
          std::shared_ptr<A> sp = std::make_shared<A>();
          std::thread t1(handler, std::weak_ptr(sp));      // 注意要传入weak_ptr
          t1.detach();
      }
      getchar();
      return 0;
  }