title: Issue when performing non-block writing
body: <p>I wrote the following code to understand how nonblocking write is operated:</p>
  
  <pre><code>import os, time
  
  def takeAnap():
      print('I am sleeping a bit while it is writing!')
      time.sleep(50)
  
  fd = os.open('t.txt', os.O_CREAT | os.O_NONBLOCK)
  for i in range(100):
      # Non-blocking write
      fd = os.open('t.txt', os.O_APPEND | os.O_WRONLY | os.O_NONBLOCK)
      os.write(fd, str(i))
      os.close(fd)
      time.sleep(2)
  takeAnap()
  </code></pre>
  
  <p>As you can see, I am creating <code>takeAnap()</code> to be activated while the loop is being processed so that I can convince my self that the writing is performed without blocking! However, the loop still blocks and the method is not performed until finishing. I am not sure if my understanding is wrong but as far as I know, non-blocking operation allows you to do other tasks while the writing is being processed. Is that correct? If so, kindly where is the problem in my code!</p>
  
  <p>Thank you.</p>