title: KoaJs can only stream one connection at once
body: <p>I'm trying to do something bigpipe with koajs.</p>
  
  <pre><code>app.use(function* () {
      this.type = 'html';
      this.body = myPage.stream() // returns a readable
  })
  </code></pre>
  
  <p>inside the myPage</p>
  
  <pre><code>myPage.prototype.stream = function() {
      var readable = new stream.Readable();
      readable._read = function() {};
      co(myRender(readable.push.bind(readable))).catch(errorHandler)
      return readable;
  });
  </code></pre>
  
  <p>Then the render will do the rendering stuff (async);</p>
  
  <p>However, it works smoothly until I tried to open multi tabs on my browser.</p>
  
  <p>It will not render other pages until one is done (i had a setTimeout to simulate async stuff in the rendere). </p>
  
  <p>Is there anyway to stream multiple connections simultaneously? Like it does with normal requests (not bigpipe) ?</p>