load multiple models in Tensorflow

Question

I have written the following convolutional neural network (CNN) class in Tensorflow [I have tried to omit some lines of code for clarity.]

class CNN:
def __init__(self,
                num_filters=16,        # initial number of convolution filters
             num_layers=5,           # number of convolution layers
             num_input=2,           # number of channels in input
             num_output=5,          # number of channels in output
             learning_rate=1e-4,    # learning rate for the optimizer
             display_step = 5000,   # displays training results every display_step epochs
             num_epoch = 10000,     # number of epochs for training
             batch_size= 64,        # batch size for mini-batch processing
             restore_file=None,      # restore file (default: None)

            ):

                # define placeholders
                self.image = tf.placeholder(tf.float32, shape = (None, None, None,self.num_input))  
                self.groundtruth = tf.placeholder(tf.float32, shape = (None, None, None,self.num_output)) 

                # builds CNN and compute prediction
                self.pred = self._build()

                # I have already created a tensorflow session and saver objects
                self.sess = tf.Session()
                self.saver = tf.train.Saver()

                # also, I have defined the loss function and optimizer as
                self.loss = self._loss_function()
                self.optimizer = tf.train.AdamOptimizer(learning_rate).minimize(self.loss)

                if restore_file is not None:
                    print("model exists...loading from the model")
                    self.saver.restore(self.sess,restore_file)
                else:
                    print("model does not exist...initializing")
                    self.sess.run(tf.initialize_all_variables())

def _build(self):
    #builds CNN

def _loss_function(self):
    # computes loss


# 
def train(self, train_x, train_y, val_x, val_y):
    # uses mini batch to minimize the loss
    self.sess.run(self.optimizer, feed_dict = {self.image:sample, self.groundtruth:gt})


    # I save the session after n=10 epochs as:
    if epoch%n==0:
        self.saver.save(sess,'snapshot',global_step = epoch)

# finally my predict function is
def predict(self, X):
    return self.sess.run(self.pred, feed_dict={self.image:X})

I have trained two CNNs for two separate tasks independently. Each took around 1 day. Say, model1 and model2 are saved as 'snapshot-model1-10000' and 'snapshot-model2-10000' (with their corresponding meta files) respectively. I can test each model and compute its performance separately.

Now, I want to load these two models in a single script. I would naturally try to do as below:

cnn1 = CNN(..., restore_file='snapshot-model1-10000',..........) 
cnn2 = CNN(..., restore_file='snapshot-model2-10000',..........)

I encounter the error [The error message is long. I just copied/pasted a snippet of it.]

NotFoundError: Tensor name "Variable_26/Adam_1" not found in checkpoint files /home/amitkrkc/codes/A549_models/snapshot-hela-95000
     [[Node: save_1/restore_slice_85 = RestoreSlice[dt=DT_FLOAT, preferred_shard=-1, _device="/job:localhost/replica:0/task:0/cpu:0"](_recv_save_1/Const_0, save_1/restore_slice_85/tensor_name, save_1/restore_slice_85/shape_and_slice)]]

Is there a way to load from these two files two separate CNNs? Any suggestion/comment/feedback is welcome.

Thank you,

Answer 1

Yes there is. Use separate graphs.

g1 = tf.Graph()
g2 = tf.Graph()

with g1.as_default():
    cnn1 = CNN(..., restore_file='snapshot-model1-10000',..........) 
with g2.as_default():
    cnn2 = CNN(..., restore_file='snapshot-model2-10000',..........)

EDIT:

If you want them into same graph. You'll have to rename some variables. One idea is have each CNN in separate scope and let saver handle variables in that scope e.g.:

saver = tf.train.Saver(tf.get_collection(tf.GraphKeys.GLOBAL_VARIABLES), scope='model1')

and in cnn wrap all your construction in scope:

with tf.variable_scope('model1'):
    ...

EDIT2:

Other idea is renaming variables which saver manages (since I assume you want to use your saved checkpoints without retraining everything. Saving allows different variable names in graph and in checkpoint, have a look at documentation for initialization.