title: Tensorflow freezes on sess.run call using queues
body: <p>I am testing the tensoprflow queues system and I have a simple tensorflow program that use queues to process the input. The code of sample program is</p>
  
  <pre><code>import tensorflow as tf
  import numpy as np
  
  def model(example_batch):
      dense1 = tf.layers.dense(inputs=example_batch, units=64, activation=tf.nn.relu)
      dense2 = tf.layers.dense(inputs=dense1, units=2)
      return dense2
  
  x_input_data = tf.random_normal([1024, 16], mean=0, stddev=1)
  q = tf.FIFOQueue(capacity=1, dtypes=tf.float32, shapes=[1024, 16])
  
  enqueue_op = q.enqueue(x_input_data)
  numberOfThreads = 1
  
  qr = tf.train.QueueRunner(q, [enqueue_op] * numberOfThreads)
  tf.train.add_queue_runner(qr)
  input = q.dequeue()
  
  sess = tf.Session()
  sess.run(tf.global_variables_initializer())
  
  # Start input enqueue threads.
  coord = tf.train.Coordinator()
  threads = tf.train.start_queue_runners(sess=sess, coord=coord)
  example_batch = tf.train.batch([input], batch_size=1, num_threads=numberOfThreads, capacity=1, enqueue_many=False)
  
  for step in range(100):
      print ("step")
      #sess.run(input)
      p = sess.run(model(example_batch))
  
  coord.request_stop()
  coord.join(threads)
  sess.close()
  </code></pre>
  
  <p>The problem is that it freeze at the first <code>p = sess.run(model2layers(example_batch))</code>, it stop there indefinitely.</p>
  
  <p>What is wrong in the sample program?</p>