std::this_thread::yield() vs std::this_thread::sleep_for()

std::this_thread::yield tells the implementation to reschedule the execution of threads, that should be used in a case where you are in a busy waiting state, like in a thread pool:

...
while(true) {
  if(pool.try_get_work()) {
    // do work
  }
  else {
    std::this_thread::yield(); // other threads can push work to the queue now
  }
}

std::this_thread::sleep_for can be used if you really want to wait for a specific amount of time. This can be used for task, where timing really matters, e.g.: if you really only want to wait for 2 seconds. (Note that the implementation might wait longer than the given time duration)

std::this_thread::sleep_for()

will make your thread sleep for a given time (the thread is stopped for a given time). (http://en.cppreference.com/w/cpp/thread/sleep_for)

std::this_thread::yield()

will stop the execution of the current thread and give priority to other process/threads (if there are other process/threads waiting in the queue). The execution of the thread is not stopped. (it just release the CPU). (http://en.cppreference.com/w/cpp/thread/yield)