title: Stop infinite looping thread from main
body: <p>I am relatively new to threads, and I'm still learning best techniques and the C++11 thread library. Right now I'm in the middle of implementing a worker thread which infinitely loops, performing some work. Ideally, the main thread would want to stop the loop from time to time to sync with the information that the worker thread is producing, and then start it again. My idea initially was this:</p>
  
  <pre><code>// Code run by worker thread
  void thread() {
      while(run_) {
          // Do lots of work
      }
  }
  // Code run by main thread
  void start() {
      if ( run_ ) return;
      run_ = true;
      // Start thread
  }
  void stop() {
      if ( !run_ ) return;
      run_ = false;
      // Join thread
  }
  // Somewhere else
  volatile bool run_ = false;
  </code></pre>
  
  <p>I was not completely sure about this so I started researching, and I discovered that volatile is actually not required for synchronization and is in fact generally harmful. Also, I discovered <a href="https://stackoverflow.com/a/2485009/1356926">this answer</a>, which describes a process nearly identical to the one I though about. In the answer's comments however, this solution is described as broken, as volatile does not guarantee that different processor cores readily (if ever) communicate changes on the volatile values.</p>
  
  <p>My question is this then: Should I use an atomic flag, or something else entirely? What exactly is the property that is lacking in volatile and that is then provided by whatever construct is needed to solve my problem effectively?</p>