Add failing test for race condition in Filter.get_or_create

wagtail/tests/utils.py

@@ -1,5 +1,6 @@
 from contextlib import contextmanager
 import warnings
+import threading
 
 from django.contrib.auth import get_user_model
 from django.utils import six
@@ -39,3 +40,34 @@ class WagtailTestUtils(object):
         for w in warning_list:
             if not issubclass(w.category, DeprecationWarning):
                 warnings.showwarning(message=w.message, category=w.category, filename=w.filename, lineno=w.lineno, file=w.file, line=w.line)
+
+
+# from http://www.caktusgroup.com/blog/2009/05/26/testing-django-views-for-concurrency-issues/
+def test_concurrently(times):
+    """
+    Add this decorator to small pieces of code that you want to test
+    concurrently to make sure they don't raise exceptions when run at the
+    same time.  E.g., some Django views that do a SELECT and then a subsequent
+    INSERT might fail when the INSERT assumes that the data has not changed
+    since the SELECT.
+    """
+    def test_concurrently_decorator(test_func):
+        def wrapper(*args, **kwargs):
+            exceptions = []
+            def call_test_func():
+                try:
+                    test_func(*args, **kwargs)
+                except Exception, e:
+                    exceptions.append(e)
+                    raise
+            threads = []
+            for i in range(times):
+                threads.append(threading.Thread(target=call_test_func))
+            for t in threads:
+                t.start()
+            for t in threads:
+                t.join()
+            if exceptions:
+                raise Exception('test_concurrently intercepted %s exceptions: %s' % (len(exceptions), exceptions))
+        return wrapper
+    return test_concurrently_decorator

wagtail/wagtailimages/tests/test_models.py

@@ -7,10 +7,10 @@ from django.contrib.auth.models import Group, Permission
 from django.core.files.uploadedfile import SimpleUploadedFile
 from django.db.utils import IntegrityError
 
-from wagtail.tests.utils import WagtailTestUtils, unittest
+from wagtail.tests.utils import WagtailTestUtils, unittest, test_concurrently
 from wagtail.wagtailcore.models import Page
 from wagtail.tests.models import EventPage, EventPageCarouselItem
-from wagtail.wagtailimages.models import Rendition
+from wagtail.wagtailimages.models import Rendition, Filter
 from wagtail.wagtailimages.backends import get_image_backend
 from wagtail.wagtailimages.backends.pillow import PillowBackend
 from wagtail.wagtailimages.rect import Rect
@@ -405,3 +405,21 @@ class TestIssue312(TestCase):
             height=rend1.height,
             focal_point_key=rend1.focal_point_key,
         )
+
+    def test_duplicate_filters(self):
+        # get renditions concurrently, using various filters that are unlikely to exist already
+        @test_concurrently(10)
+        def get_renditions():
+            # Create an image
+            image = Image.objects.create(
+                title="Concurrency test image",
+                file=get_test_image_file(),
+            )
+            for width in range(10, 100, 10):
+                image.get_rendition('width-%d' % width)
+
+        get_renditions()
+        # if the above has completed with no race conditions, there should be precisely one
+        # of each of the above filters in the database
+        for width in range(10, 100, 10):
+            self.assertEqual(Filter.objects.filter(spec='width-%d' % width).count(), 1)