C＆＃x2b;＆＃x2b;中的多线程 - 显示动画直到另一个线程完成

Question

序言：这是我第一次尝试使用具有多线程的任何语言编写程序。我没有先前在STD ::线程的经验，也没有描述多线程的程序。请让我知道您是否需要更多信息来回答此问题，或者我是否可以重新介绍任何内容以使我的问题更清晰。

假设我有一个简单的动画函数Animate，该功能（目前）无限期地运行；另一个函数任务，代表某些任意执行的代码。

#include <string>

// a simple rotating stick animation: | -> / -> - -> \

void animate()
{
  std::string syms = "|/-\\";
  while (true)
  {
    for (unsigned int ii = 0; ii < syms.length(); ++ii)
    {
      std::cout << syms[ii];
      std::cout << std::string(1, '\b');
    }
  }
}

// arbitrary function

void task()
{
  // code to do something else goes here
}

int main (int argc, char* argv[])
{
  // execute task and animate at the same time;
  // return from animate once task has completed
  return 0;
}

我如何使用std :: thread（或其他一些标题/库）允许task和Animate互相通信，以便任务在“背景”和Animate运行直到任务已经完成？

Answer 1

我已经使用了您的示例代码，并试图用std :: thread从您的意图中填充空白。我添加了一些内联评论来解释正在发生的事情。如果不清楚的话，或者我弄错了，请随时在评论中询问。

我想强调，虽然这个示例 使用std :: thread在玩具示例中创建并连接一个单独的线程。
它不会以正确的方式在线程之间同步共享数据。
MT环境中的共享数据是事物变得毛茸茸的，最糟糕的是，它可以创建一些最难调试错误的地方。这就是为什么书籍和工作示例对于任何实质性多线程程序都很重要的原因。

#include <string>
#include <thread>
#include <chrono>
#include <iostream>

// a simple rotating stick animation: | -> / -> - -> \

//
void animate(bool * should_animate)
{
  // Using this namespace lets us use the "100ms" time literal in the sleep_for() function argument.
  using namespace std::chrono_literals;

  std::string syms = "|/-\\";
  while (*should_animate)
  {
    for (unsigned int ii = 0; ii < syms.length(); ++ii)
    {
      std::cout << syms[ii];
      std::cout << std::string(1, '\b');

      // I had to flush cout so that the animation would show up
      std::cout.flush();
      // I added some delay here so that the animation is more visible
      std::this_thread::sleep_for(100ms);
    }
  }
}

// arbitrary function

void task()
{
  using namespace std::chrono_literals;
  // I have this thread waiting for 2 seconds to simulate a lot of work being done
  std::this_thread::sleep_for(2s);
}

int main (int argc, char* argv[])
{

  // This line creates a thread from the animate() function
  // The std::thread constructor is flexible, in that it can take a function with any number and type of arguments and
  // make a thread out of it
  // Once the thread is created, it gets sent to the operating system for scheduling right away in a separate thread
  // I'm passing in a pointer to `should_animate` to use that value as a basic way to communicate to the animate thread to signal when it should stop running.
  // I'm doing this to keep the example simple, but I stress that this isn't a good idea for larger scale programs
  // Better to use propper signals or event queues
  bool should_animate = true;
  std::thread thread_animate(animate, &should_animate);

  // This line creates a thread for the worker task
  // That separate thread can be referenced by tis std::thread object
  // Once the functions finish running, the thread associated with it is "joined"
  std::thread thread_task(task);

  // 'join' pauses the main thread to wait for the associated thread to finish running in the background.
  thread_task.join();

  // By this point in the program, the `task()` function has finished running, so we can flag
  // the animate task to finish running so its thread can be joined
  should_animate = false;
  // Wait for the animate thread to get the message and finish
  thread_animate.join();


  std::cout << "Done!" << std::endl;
  return 0;
}

---

如果您想进一步，我建议您推荐一些链接。

• 这是我在Google首页上找到的最好的教程（大多数结果似乎很糟糕）。似乎是一个很好的跳跃点 https：//solarianprogrammer.com/ 2011/12/16/CPP-11-thread-Tutorial/
• CPPReference是我所知道的最好的C ++参考站点，并且我通常整天至少有一个标签。因为它是参考，因此很难直接挖掘出来。此页面的每个部分标题涵盖了一个多线程主题。 “线程”和“相互排斥”是MT中最常见的东西。 https://en.cppreference.com/w/cpp/thread