title: fs.writeFile while clients try to get the file
body: <p>I'm doing image modifications on a .png and then writing it on my server with</p>
  
  <pre><code>fs.writeFile
  </code></pre>
  
  <p>Problem is if some clients try to http get the .png from my server while i'm writing it, it will fail.</p>
  
  <p>How can i prevent that ?</p>