C++11单/多线程总结(三十五)

1.代码示例  

#include <iostream>
#include <thread>
#include <mutex>
#include <future>
#include <condition_variable>
#include <queue>
#include <chrono>

//1.thread usage demo
#if 0
void foo(){
  std::cout << "hello" << std::endl;
}

int main(){
  std::thread t(foo);
  t.join();
  
  return 0;
}

#endif

//2.mutex usage demo
#if 0
std::mutex mtx;

void block_area(){
  std::unique_lock<std::mutex> lock(mtx);
  //...临界区  
}

int main(){
  std::thread thd1(block_area);
  thd1.join();
  return 0;
}

#endif

#if 0
//3.thread Asynchrony operation
int main()
{
  //将一个返回值为7的 lambda 表达式封装到 task 中
  //std::packaged_task 的模板参数为要封装函数的类型
  std::packaged_task<int()> task([](){return 7;});
  //获得 task 的 future
  std::future<int> result = task.get_future(); // 在一个线程中执行 task
  std::thread(std::move(task)).detach(); std::cout << "Waiting...";
  result.wait();
  //输出执行结果
  std::cout << "Done!" << std:: endl << "Result is " << result.get() << '\n';
}

#endif

//4.producer and consumer model demo.
#if 1
int main()
{
  // 生产者数量
  std::queue<int> produced_nums;
  // 互斥锁
  std::mutex m;
  // 条件变量
  std::condition_variable cond_var;
  // 结束标志
  bool done = false;
  // 通知标志
  bool notified = false;
  // 生产者线程
  std::thread producer([&]() {
      for (int i = 0; i < 5; ++i) {
	std::this_thread::sleep_for(std::chrono::seconds(1));
        // 创建互斥锁
	std::unique_lock<std::mutex> lock(m);
	std::cout << "producing " << i << '\n';
	produced_nums.push(i);
	notified = true;
        // 通知一个线程
	cond_var.notify_one();
      }
      done = true;
      cond_var.notify_one();
    });
  
  // 消费者线程
  std::thread consumer([&]() {
      std::unique_lock<std::mutex> lock(m);
      while (!done) {
	while (!notified) { // 循环避免虚假唤醒
	  cond_var.wait(lock);
	}
	while (!produced_nums.empty()) {std::cout << "consuming " << produced_nums.front() << '\n';
	  produced_nums.pop();
	}
	notified = false;
      }
    });
  producer.join();
  consumer.join();
}
#endif