Added functionality for retrieving variables from control dependencies (

ray-project#220)

* Added test for retriving variables from an optimizer

* Added comments to test

* Addressed comments

* Fixed travis bug

* Added fix to circular controls

* Added set for explored operations and duplicate prefix stripping

* Removed embeded ipython

* Removed prefix, use seperate graph for each network

* Removed redundant imports

* Addressed comments and added separate graph to initializer

* fix typos

* get rid of prefix in documentation

doc/using-ray-with-tensorflow.md

@@ -72,21 +72,18 @@ b.assign(np.zeros(1))  # This adds a node to the graph every time you call it.
 ## Complete Example
 
 Putting this all together, we would first create the graph on each worker using
-environment variables. Within the environment variables, we would use the 
+environment variables. Within the environment variables, we would use the
 `get_weights` and `set_weights` methods of the `TensorFlowVariables` class. We
-would then use those methods to ship the weights (as a dictionary of variable 
+would then use those methods to ship the weights (as a dictionary of variable
 names mapping to tensorflow tensors) between the processes without shipping the
 actual TensorFlow graphs, which are much more complex Python objects. Note that
-to avoid namespace collision with already created variables on the workers, we 
-use a variable_scope and a prefix in the environment variables and then pass 
-true to the prefix in `TensorFlowVariables` so it can properly decode the variable
-names.
+to avoid namespace collision with already created variables on the workers, we
+use a separate graph for each network.
 
 ```python
 import tensorflow as tf
 import numpy as np
 import ray
-import uuid
 
 ray.init(num_workers=5)
 
@@ -95,11 +92,8 @@ NUM_BATCHES = 1
 NUM_ITERS = 201
 
 def net_vars_initializer():
-  # Prefix should be random so that there is no conflict with variable names in
-  # the cluster setting.
-  prefix = str(uuid.uuid1().hex)
-  # Use the tensorflow variable_scope to prefix all of the variables
-  with tf.variable_scope(prefix):
+  # Use a separate graph for each network.
+  with tf.Graph().as_default():
     # Seed TensorFlow to make the script deterministic.
     tf.set_random_seed(0)
     # Define the inputs.
@@ -116,9 +110,8 @@ def net_vars_initializer():
     # Define the weight initializer and session.
     init = tf.global_variables_initializer()
     sess = tf.Session()
-    # Additional code for setting and getting the weights, and use a prefix
-    # so that the variable names can be converted between workers.
-    variables = ray.experimental.TensorFlowVariables(loss, sess, prefix=True)
+    # Additional code for setting and getting the weights
+    variables = ray.experimental.TensorFlowVariables(loss, sess)
     # Return all of the data needed to use the network.
   return variables, sess, train, loss, x_data, y_data, init
 

examples/lbfgs/driver.py

@@ -61,7 +61,8 @@ def grad(self, xs, ys):
     return self.sess.run(self.cross_entropy_grads, feed_dict={self.x: xs, self.y_: ys})
 
 def net_initialization():
-  return LinearModel([784,10])
+  with tf.Graph().as_default():
+    return LinearModel([784,10])
 
 # By default, when an environment variable is used by a remote function, the
 # initialization code will be rerun at the end of the remote task to ensure

python/ray/experimental/tfutils.py

@@ -28,28 +28,41 @@ class TensorFlowVariables(object):
     assignment_placeholders (List[tf.placeholders]): The nodes that weights get
       passed to.
     assignment_nodes (List[tf.Tensor]): The nodes that assign the weights.
-    prefix (Bool): Boolean for if there is a prefix on the variable names.
   """
-  def __init__(self, loss, sess=None, prefix=False):
+  def __init__(self, loss, sess=None):
     """Creates a TensorFlowVariables instance."""
     import tensorflow as tf
     self.sess = sess
     self.loss = loss
-    self.prefix = prefix
     queue = deque([loss])
     variable_names = []
+    explored_inputs = set([loss])
 
     # We do a BFS on the dependency graph of the input function to find 
     # the variables.
     while len(queue) != 0:
-      op = queue.popleft().op
-      queue.extend(op.inputs)
-      if op.node_def.op == "Variable":
-        variable_names.append(op.node_def.name)
+      tf_obj = queue.popleft()
+
+      # The object put into the queue is not necessarily an operation, so we
+      # want the op attribute to get the operation underlying the object.
+      # Only operations contain the inputs that we can explore.
+      if hasattr(tf_obj, "op"):
+         tf_obj = tf_obj.op
+      for input_op in tf_obj.inputs:
+        if input_op not in explored_inputs:
+          queue.append(input_op)
+          explored_inputs.add(input_op)
+      # Tensorflow control inputs can be circular, so we keep track of
+      # explored operations.
+      for control in tf_obj.control_inputs:
+        if control not in explored_inputs:
+          queue.append(control)
+          explored_inputs.add(control)
+      if tf_obj.node_def.op == "Variable":
+        variable_names.append(tf_obj.node_def.name)
     self.variables = OrderedDict()
     for v in [v for v in tf.global_variables() if v.op.node_def.name in variable_names]:
-      name = v.op.node_def.name.split("/", 1 if prefix else 0)[-1]
-      self.variables[name] = v
+      self.variables[v.op.node_def.name] = v
     self.assignment_placeholders = dict()
     self.assignment_nodes = []
 

test/tensorflow_test.py

@@ -17,32 +17,39 @@ def make_linear_network(w_name=None, b_name=None):
   b = tf.Variable(tf.zeros([1]), name=b_name)
   y = w * x_data + b
   # Return the loss and weight initializer.
-  return tf.reduce_mean(tf.square(y - y_data)), tf.global_variables_initializer()
+  return tf.reduce_mean(tf.square(y - y_data)), tf.global_variables_initializer(), x_data, y_data
 
 def net_vars_initializer():
-  # Random prefix so variable names do not clash if we use nets with
-  # the same name.
-  prefix = str(uuid.uuid1().hex)
-  # Use the tensorflow variable_scope to prefix all of the variables
-  with tf.variable_scope(prefix):
+  # Uses a separate graph for each network.
+  with tf.Graph().as_default():
     # Create the network.
-    loss, init = make_linear_network()
+    loss, init, _, _ = make_linear_network()
     sess = tf.Session()
     # Additional code for setting and getting the weights.
-    variables = ray.experimental.TensorFlowVariables(loss, sess, prefix=True)
+    variables = ray.experimental.TensorFlowVariables(loss, sess)
   # Return all of the data needed to use the network.
   return variables, init, sess
 
 def net_vars_reinitializer(net_vars):
   return net_vars
 
+def train_vars_initializer():
+  # Almost the same as above, but now returns the placeholders and gradient.
+  with tf.Graph().as_default():
+    loss, init, x_data, y_data = make_linear_network()
+    sess = tf.Session()
+    variables = ray.experimental.TensorFlowVariables(loss, sess)
+    grad = tf.gradients(loss, list(variables.variables.values()))
+  return variables, init, sess, grad, [x_data, y_data]
+
+
 class TensorFlowTest(unittest.TestCase):
 
   def testTensorFlowVariables(self):
     ray.init(num_workers=2)
 
     sess = tf.Session()
-    loss, init = make_linear_network()
+    loss, init, _, _ = make_linear_network()
     sess.run(init)
 
     variables = ray.experimental.TensorFlowVariables(loss, sess)
@@ -54,7 +61,7 @@ def testTensorFlowVariables(self):
     variables.set_weights(weights)
     self.assertEqual(weights, variables.get_weights())
 
-    loss2, init2 = make_linear_network("w", "b")
+    loss2, init2, _, _ = make_linear_network("w", "b")
     sess.run(init2)
 
     variables2 = ray.experimental.TensorFlowVariables(loss2, sess)
@@ -148,7 +155,7 @@ def testNetworkDriverWorkerIndependent(self):
 
     # Create a network on the driver locally.
     sess1 = tf.Session()
-    loss1, init1 = make_linear_network()
+    loss1, init1, _, _ = make_linear_network()
     net_vars1 = ray.experimental.TensorFlowVariables(loss1, sess1)
     sess1.run(init1)
 
@@ -170,5 +177,39 @@ def set_and_get_weights(weights):
 
     ray.worker.cleanup()
 
+  def testVariablesControlDependencies(self):
+    ray.init(num_workers=1)
+
+    # Creates a network and appends a momentum optimizer.
+    sess = tf.Session()
+    loss, init, _, _ = make_linear_network()
+    minimizer = tf.train.MomentumOptimizer(0.9, 0.9).minimize(loss)
+    net_vars = ray.experimental.TensorFlowVariables(minimizer, sess)
+    sess.run(init)
+
+    # Tests if all variables are properly retrieved, 2 variables and 2 momentum
+    # variables.
+    self.assertEqual(len(net_vars.variables.items()), 4)
+
+    ray.worker.cleanup()
+
+  def testRemoteTrainingStep(self):
+    ray.init(num_workers=1)
+
+    ray.env.net = ray.EnvironmentVariable(train_vars_initializer, net_vars_reinitializer)
+
+    @ray.remote
+    def training_step(weights):
+      variables, _, sess, grad, placeholders = ray.env.net
+      variables.set_weights(weights)
+      return sess.run(grad, feed_dict=dict(zip(placeholders, [[1]*100]*2)))
+
+    variables, init, sess, _, _ = ray.env.net
+
+    sess.run(init)
+    ray.get(training_step.remote(variables.get_weights()))
+
+    ray.worker.cleanup()
+
 if __name__ == "__main__":
   unittest.main(verbosity=2)