使用多线程读取大量图片数据

程序在需要读取多幅图片时，
需要使用多线程来进行操作：

coord = tf.train.Coordinator()
threads = tf.train.start_queue_runners(coord=coord)

# use multithreading to output image_batch and label_batch
try:
   while not coord.should_stop() and i < 1:

   image_batch, label_batch = sess.run([image_batch, label_batch])

   # just test one batch
   for j in np.arange(FLAGS.train_batch_size):
   print('label: %d' % label_batch[j])
   # plt.imshow(image_batch[j, :, :, :])
   # plt.show()
   i += 1

except tf.errors.OutOfRangeError:
   print('done!')
finally:
   coord.request_stop()
   coord.join(threads)