Fix thread local context.

src/google/cloud/ndb/context.py

@@ -36,8 +36,6 @@
 class _LocalState(threading.local):
     """Thread local state."""
 
-    __slots__ = ("context",)
-
     def __init__(self):
         self.context = None
 

tests/system/test_crud.py

@@ -17,6 +17,7 @@
 """
 import functools
 import operator
+import threading
 
 import pytest
 
@@ -150,6 +151,35 @@ class SomeKind(ndb.Model):
     dispose_of(key._key)
 
 
+def test_parallel_threads(dispose_of, namespace):
+    client = ndb.Client(namespace=namespace)
+
+    class SomeKind(ndb.Model):
+        foo = ndb.IntegerProperty()
+        bar = ndb.StringProperty()
+
+    def insert(foo):
+        with client.context(cache_policy=False):
+            entity = SomeKind(foo=foo, bar="none")
+
+            key = entity.put()
+
+            retrieved = key.get()
+            assert retrieved.foo == foo
+            assert retrieved.bar == "none"
+
+            dispose_of(key._key)
+
+    thread1 = threading.Thread(target=insert, args=[42], name="one")
+    thread2 = threading.Thread(target=insert, args=[144], name="two")
+
+    thread1.start()
+    thread2.start()
+
+    thread1.join()
+    thread2.join()
+
+
 @pytest.mark.usefixtures("client_context")
 def test_large_json_property(dispose_of, ds_client):
     class SomeKind(ndb.Model):