Add option to pickler dumps() for best-effort determinism

sdks/python/apache_beam/internal/cloudpickle_pickler.py

@@ -107,8 +107,16 @@ def _pickle_enum_descriptor(obj):
   return _reconstruct_enum_descriptor, (full_name, )
 
 
-def dumps(o, enable_trace=True, use_zlib=False) -> bytes:
+def dumps(
+    o,
+    enable_trace=True,
+    use_zlib=False,
+    enable_best_effort_determinism=False) -> bytes:
   """For internal use only; no backwards-compatibility guarantees."""
+  if enable_best_effort_determinism:
+    # TODO: Add support once https://github.com/cloudpipe/cloudpickle/pull/563
+    # is merged in.
+    raise NotImplementedError('This option has only been implemeneted for dill')
   with _pickle_lock:
     with io.BytesIO() as file:
       pickler = cloudpickle.CloudPickler(file)

sdks/python/apache_beam/internal/cloudpickle_pickler_test.py

@@ -135,6 +135,10 @@ def test_dataclass(self):
 self.assertEqual(DataClass(datum='abc'), loads(dumps(DataClass(datum='abc'))))
     ''')
 
+  def test_best_effort_determinism_not_implemented(self):
+    with self.assertRaises(NotImplementedError):
+      dumps(123, enable_best_effort_determinism=True)
+
 
 if __name__ == '__main__':
   unittest.main()

sdks/python/apache_beam/internal/dill_pickler.py

@@ -41,6 +41,7 @@
 from typing import Any
 from typing import Dict
 from typing import Tuple
+from apache_beam.internal.set_pickler import save_frozenset, save_set
 
 import dill
 
@@ -376,9 +377,16 @@ def new_log_info(msg, *args, **kwargs):
 logging.getLogger('dill').setLevel(logging.WARN)
 
 
-def dumps(o, enable_trace=True, use_zlib=False) -> bytes:
+def dumps(
+    o,
+    enable_trace=True,
+    use_zlib=False,
+    enable_best_effort_determinism=False) -> bytes:
   """For internal use only; no backwards-compatibility guarantees."""
   with _pickle_lock:
+    if enable_best_effort_determinism:
+      dill.dill.pickle(set, save_set)
+      dill.dill.pickle(frozenset, save_frozenset)
     try:
       s = dill.dumps(o, byref=settings['dill_byref'])
     except Exception:  # pylint: disable=broad-except

sdks/python/apache_beam/internal/pickler.py

@@ -38,10 +38,17 @@
 desired_pickle_lib = dill_pickler
 
 
-def dumps(o, enable_trace=True, use_zlib=False) -> bytes:
+def dumps(
+    o,
+    enable_trace=True,
+    use_zlib=False,
+    enable_best_effort_determinism=False) -> bytes:
 
   return desired_pickle_lib.dumps(
-      o, enable_trace=enable_trace, use_zlib=use_zlib)
+      o,
+      enable_trace=enable_trace,
+      use_zlib=use_zlib,
+      enable_best_effort_determinism=enable_best_effort_determinism)
 
 
 def loads(encoded, enable_trace=True, use_zlib=False):

sdks/python/apache_beam/internal/pickler_test.py

@@ -115,6 +115,11 @@ def test_dataclass(self):
 self.assertEqual(DataClass(datum='abc'), loads(dumps(DataClass(datum='abc'))))
     ''')
 
+  def test_best_effort_determinism(self):
+    self.assertEqual(
+        dumps({'a', 'b', 'c'}, enable_best_effort_determinism=True),
+        dumps({'c', 'b', 'a'}, enable_best_effort_determinism=True))
+
 
 if __name__ == '__main__':
   unittest.main()

sdks/python/apache_beam/internal/set_pickler.py

@@ -0,0 +1,164 @@
+#
+# Licensed to the Apache Software Foundation (ASF) under one or more
+# contributor license agreements.  See the NOTICE file distributed with
+# this work for additional information regarding copyright ownership.
+# The ASF licenses this file to You under the Apache License, Version 2.0
+# (the "License"); you may not use this file except in compliance with
+# the License.  You may obtain a copy of the License at
+#
+#    http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+#
+
+"""Custom pickling logic for sets to make the serialization semi-deterministic.
+
+To make set serialization semi-deterministic, we must pick an order for the set
+elements. Sets may contain elements of types not defining a comparison "<"
+operator. To provide an order, we define our own custom comparison function
+which supports elements of near-arbitrary types and use that to sort the
+contents of each set during serialization. Attempts at determinism are made on a
+best-effort basis to improve hit rates for cached workflows and the ordering
+does not define a total order for all values.
+"""
+
+import enum
+import functools
+
+
+def compare(lhs, rhs):
+  """Returns -1, 0, or 1 depending on whether lhs <, =, or > rhs."""
+  if lhs < rhs:
+    return -1
+  elif lhs > rhs:
+    return 1
+  else:
+    return 0
+
+
+def generic_object_comparison(lhs, rhs, lhs_path, rhs_path, max_depth):
+  """Identifies which object goes first in an (almost) total order of objects.
+
+  Args:
+    lhs: An arbitrary Python object or built-in type.
+    rhs: An arbitrary Python object or built-in type.
+    lhs_path: Traversal path from the root lhs object up to, but not including,
+      lhs. The original contents of lhs_path are restored before the function
+      returns.
+    rhs_path: Same as lhs_path except for the rhs.
+    max_depth: Maximum recursion depth.
+
+  Returns:
+    -1, 0, or 1 depending on whether lhs or rhs goes first in the total order.
+    0 if max_depth is exhausted.
+    0 if lhs is in lhs_path or rhs is in rhs_path (there is a cycle).
+  """
+  if id(lhs) == id(rhs):
+    # Fast path
+    return 0
+  if type(lhs) != type(rhs):
+    return compare(str(type(lhs)), str(type(rhs)))
+  if type(lhs) in [int, float, bool, str, bool, bytes, bytearray]:
+    return compare(lhs, rhs)
+  if isinstance(lhs, enum.Enum):
+    # Enums can have values with arbitrary types. The names are strings.
+    return compare(lhs.name, rhs.name)
+
+  # To avoid exceeding the recursion depth limit, set a limit on recursion.
+  max_depth -= 1
+  if max_depth < 0:
+    return 0
+
+  # Check for cycles in the traversal path to avoid getting stuck in a loop.
+  if id(lhs) in lhs_path or id(rhs) in rhs_path:
+    return 0
+  lhs_path.append(id(lhs))
+  rhs_path.append(id(rhs))
+  # The comparison logic is split across two functions to simplifying updating
+  # and restoring the traversal paths.
+  result = _generic_object_comparison_recursive_path(
+      lhs, rhs, lhs_path, rhs_path, max_depth)
+  lhs_path.pop()
+  rhs_path.pop()
+  return result
+
+
+def _generic_object_comparison_recursive_path(
+    lhs, rhs, lhs_path, rhs_path, max_depth):
+  if type(lhs) == tuple or type(lhs) == list:
+    result = compare(len(lhs), len(rhs))
+    if result != 0:
+      return result
+    for i in range(len(lhs)):
+      result = generic_object_comparison(
+          lhs[i], rhs[i], lhs_path, rhs_path, max_depth)
+      if result != 0:
+        return result
+    return 0
+  if type(lhs) == frozenset or type(lhs) == set:
+    return generic_object_comparison(
+        tuple(sort_if_possible(lhs, lhs_path, rhs_path, max_depth)),
+        tuple(sort_if_possible(rhs, lhs_path, rhs_path, max_depth)),
+        lhs_path,
+        rhs_path,
+        max_depth)
+  if type(lhs) == dict:
+    lhs_keys = list(lhs.keys())
+    rhs_keys = list(rhs.keys())
+    result = compare(len(lhs_keys), len(rhs_keys))
+    if result != 0:
+      return result
+    lhs_keys = sort_if_possible(lhs_keys, lhs_path, rhs_path, max_depth)
+    rhs_keys = sort_if_possible(rhs_keys, lhs_path, rhs_path, max_depth)
+    for lhs_key, rhs_key in zip(lhs_keys, rhs_keys):
+      result = generic_object_comparison(
+          lhs_key, rhs_key, lhs_path, rhs_path, max_depth)
+      if result != 0:
+        return result
+      result = generic_object_comparison(
+          lhs[lhs_key], rhs[rhs_key], lhs_path, rhs_path, max_depth)
+      if result != 0:
+        return result
+
+  lhs_fields = dir(lhs)
+  rhs_fields = dir(rhs)
+  result = compare(len(lhs_fields), len(rhs_fields))
+  if result != 0:
+    return result
+  for i in range(len(lhs_fields)):
+    result = compare(lhs_fields[i], rhs_fields[i])
+    if result != 0:
+      return result
+    result = generic_object_comparison(
+        getattr(lhs, lhs_fields[i], None),
+        getattr(rhs, rhs_fields[i], None),
+        lhs_path,
+        rhs_path,
+        max_depth)
+    if result != 0:
+      return result
+  return 0
+
+
+def sort_if_possible(obj, lhs_path=None, rhs_path=None, max_depth=4):
+  def cmp(lhs, rhs):
+    if lhs_path is None:
+      # Start the traversal at the root call to cmp.
+      return generic_object_comparison(lhs, rhs, [], [], max_depth)
+    else:
+      # Continue the existing traversal path for recursive calls to cmp.
+      return generic_object_comparison(lhs, rhs, lhs_path, rhs_path, max_depth)
+
+  return sorted(obj, key=functools.cmp_to_key(cmp))
+
+
+def save_set(pickler, obj):
+  pickler.save_set(sort_if_possible(obj))
+
+
+def save_frozenset(pickler, obj):
+  pickler.save_frozenset(sort_if_possible(obj))