title: How to make flask response to client asynchronously?
body: <p>Flask is a single thread web server. But I want to make it won't block when handle some time consuming request.</p>
  
  <p>For example:</p>
  
  <pre><code>from flask import Flask
  import time
  import sys
  app = Flask(__name__)
  
  @app.route("/")
  def hello():
      print "request"
      sys.stdout.flush()
      for _ in range(10000000):
          for j in range(10000000):
              i = 1
      return "Hello World!"
  
  if __name__ == "__main__":
      app.run(debug=True)
  </code></pre>
  
  <p>I want when every client request to server, it always output "request" on console immediately. I have try <code>gunicorn</code> and run with <code>gunicorn -k gevent -w 4 a:app</code> but it still appears synchronous.</p>