Use a UUID (rather than a sentinel object) on Pub / Sub Future. (#4634

)

Also changing identity check to equality check for Future._SENTINEL.

pubsub/google/cloud/pubsub_v1/futures.py

@@ -15,6 +15,7 @@
 from __future__ import absolute_import
 
 import threading
+import uuid
 
 import google.api_core.future
 from google.cloud.pubsub_v1.publisher import exceptions
@@ -29,7 +30,11 @@ class Future(google.api_core.future.Future):
     This object should not be created directly, but is returned by other
     methods in this library.
     """
-    _SENTINEL = object()
+
+    # This could be a sentinel object or None, but the sentinel object's ID
+    # can change if the process is forked, and None has the possibility of
+    # actually being a result.
+    _SENTINEL = uuid.uuid4()
 
     def __init__(self):
         self._result = self._SENTINEL
@@ -68,8 +73,8 @@ def done(self):
         This still returns True in failure cases; checking :meth:`result` or
         :meth:`exception` is the canonical way to assess success or failure.
         """
-        return (self._exception is not self._SENTINEL or
-                self._result is not self._SENTINEL)
+        return (self._exception != self._SENTINEL or
+                self._result != self._SENTINEL)
 
     def result(self, timeout=None):
         """Return the message ID, or raise an exception.
@@ -118,7 +123,7 @@ def exception(self, timeout=None):
             raise exceptions.TimeoutError('Timed out waiting for result.')
 
         # If the batch completed successfully, this should return None.
-        if self._result is not self._SENTINEL:
+        if self._result != self._SENTINEL:
             return None
 
         # Okay, this batch had an error; this should return it.