title: there is no graph with tensorboard
body: <p>I am reading a book on Tensorflow and I find this code:</p>
  
  <pre><code>from __future__ import absolute_import
  from __future__ import division
  from __future__ import print_function
  
  import tensorflow as tf
  
  const1 = tf.constant(2)
  const2 = tf.constant(3)
  add_opp = tf.add(const1,const2)
  mul_opp = tf.mul(add_opp, const2)
  
  with tf.Session() as sess:
      result, result2 = sess.run([mul_opp,add_opp])
      print(result)
      print(result2)
  
      tf.train.SummaryWriter('./',sess.graph)
  </code></pre>
  
  <p>so it is very simple, nothing fancy and it is supposed to produce some output that can be visualized with tensorboard.</p>
  
  <p>So I run the script, it prints the results but apparently SummaryWriter produces nothing. </p>
  
  <p>I run <code>tensorboard -logdir='./'</code> and of course there is no graph.
  What could I be doing wrong?</p>
  
  <p>And also how do you terminate tensorboard? I tried ctrl-C and ctrl-Z and it does not work. (also I am in a japanese keyboard so there is no backslash just in case) </p>