Use WeakKeyDictionaries for global Keras {graph->...} maps

These globals were holding onto graphs including FuncGraphs, which
held onto captured tensors leaving garbage around.

This change also adds a test to catch garbage like this in the future.
To make the test work, I needed to manually breakup some reference
cycles caused by OrderedDicts. We should probably have a custom impl
of OrderedDict similar to the one in Python3 and avoid these issues.

PiperOrigin-RevId: 212694290

2 files changed, 44 insertions, 15 deletions

diff --git a/tensorflow/python/framework/ops.py b/tensorflow/python/framework/ops.py
index 75678cbc01..343f52fe8f 100644
--- a/tensorflow/python/framework/ops.py
+++ b/tensorflow/python/framework/ops.py
@@ -58,6 +58,7 @@ from tensorflow.python.util import decorator_utils
 from tensorflow.python.util import deprecation
 from tensorflow.python.util import function_utils
 from tensorflow.python.util import lock_util
+from tensorflow.python.util import memory
 from tensorflow.python.util import tf_contextlib
 from tensorflow.python.util import tf_stack
 from tensorflow.python.util.deprecation import deprecated_args
@@ -5824,23 +5825,11 @@ def dismantle_graph(graph):
     graph: A `Graph` object to destroy. Neither it nor any of its ops are usable
       after this function runs.
   """
-  # pylint: disable=protected-access
-  # OrderedDict, constructed on Graph creation, makes a simple reference loop
-  # and hides it in an __attribute in some Python versions. We don't need to
-  # throw an error if we can't find it, but if we do find it we can break the
-  # loop to avoid creating work for the garbage collector.
-  graph_operations = graph.get_operations()
-  problematic_cycle = graph._functions.__dict__.get("_OrderedDict__root", None)
-  # pylint: enable=protected-access
-  if problematic_cycle:
-    try:
-      del problematic_cycle[0][:]
-    except TypeError:
-      # This is probably not one of the problematic Python versions. Continue
-      # with the rest of our cleanup.
-      pass
+  memory.dismantle_ordered_dict(graph._functions)  # pylint: disable=protected-access
+
   # Now clean up Operation<->Graph reference cycles by clearing all of the
   # attributes for the Graph and its ops.
+  graph_operations = graph.get_operations()
   for op in graph_operations:
     op.__dict__ = {}
   graph.__dict__ = {}
diff --git a/tensorflow/python/framework/test_util.py b/tensorflow/python/framework/test_util.py
index 6a2c897f3f..1cc3bb4628 100644
--- a/tensorflow/python/framework/test_util.py
+++ b/tensorflow/python/framework/test_util.py
@@ -69,6 +69,7 @@ from tensorflow.python.platform import googletest
 from tensorflow.python.platform import tf_logging as logging
 from tensorflow.python.training import server_lib
 from tensorflow.python.util import compat
+from tensorflow.python.util import memory
 from tensorflow.python.util import nest
 from tensorflow.python.util import tf_inspect
 from tensorflow.python.util.protobuf import compare
@@ -2008,3 +2009,42 @@ def set_producer_version(graph, producer_version):
   with graph.as_default():
     importer.import_graph_def(graph_def)
   assert graph.graph_def_versions.producer, producer_version
+
+
+def dismantle_func_graph(func_graph):
+  """Removes reference cycles in `func_graph` FuncGraph.
+
+  Helpful for making sure the garbage collector doesn't need to run when
+  the FuncGraph goes out of scope, e.g. in tests using defun with
+  @test_util.run_in_graph_and_eager_modes(assert_no_eager_garbage=True).
+
+  Args:
+    func_graph: A `FuncGraph` object to destroy. `func_graph` is unusable
+      after this function.
+  """
+  # TODO(b/115366440): Delete this method when a custom OrderedDict is added.
+  # Clearing captures using clear() leaves some cycles around.
+  while func_graph.captures:
+    func_graph.captures.popitem()
+  memory.dismantle_ordered_dict(func_graph.captures)
+  ops.dismantle_graph(func_graph)
+
+
+def dismantle_polymorphic_function(func):
+  """Removes reference cycles in PolymorphicFunction `func`.
+
+  Helpful for making sure the garbage collector doesn't need to run when
+  PolymorphicFunction goes out of scope, e.g. in tests using defun with
+  @test_util.run_in_graph_and_eager_modes(assert_no_eager_garbage=True).
+
+  Args:
+    func: A `PolymorphicFunction` object to destroy. `func` is unusable
+      after this function.
+  """
+  # TODO(b/115366440): Delete this method when a custom OrderedDict is added
+  cache = func._function_cache  # pylint: disable=protected-access
+  for concrete_func in cache.values():
+    dismantle_func_graph(concrete_func.graph)
+  while cache:
+    cache.popitem()
+  memory.dismantle_ordered_dict(cache)