C++11线程指南(5)--线程的移动语义实现

1. 线程的移动语义实现

  基于前面几章介绍的移动语义，我们用它来实现线程。

#include <iostream>#include <thread>#include <vector>#include <algorithm>#include <cassert>int main(){std::vector<std::thread> workers;for (int i = 0; i < 5; i++) {auto t = std::thread([i](){std::cout << "thread function: " << i << "\n";});workers.push_back(std::move(t));}std::cout << "main thread\n";std::for_each(workers.begin(), workers.end(), [](std::thread &t){assert(t.joinable());t.join();});return 0;}

  运行结果为：
thread function: thread function: thread function: 01

thread function: 3
2
main thread
thread function: 4
  接下来对代码进行一些改变。将线程函数task()独立出来。

#include <iostream>#include <thread>#include <vector>#include <algorithm>#include <cassert>void task(int i){std::cout<<"worker : "<<i<<std::endl;}int main(){std::vector<std::thread> workers;for (int i = 0; i < 5; i++) {auto t = std::thread(&task, i);workers.push_back(std::move(t));}std::cout << "main thread" << std::endl;std::for_each(workers.begin(), workers.end(), [](std::thread &t){assert(t.joinable());t.join();});return 0;}

  运行结果为：
  worker : worker : 02
  worker : 3
  worker : 1
  main thread
  worker : 4

2. 通过引用传递线程参数

  下面将线程函数的参数改为引用

void task(int &i){std::cout << "worker : " << i << "\n";}

  与此同时，线程的构造函数同样需要相应的修改
  auto t = std::thread(&task, std::ref(i));
  但是，上面程序看似可以工作，不过不是一个好的设计，因为多个线程在同时使用一个指向相同对象的引用。