New locking mechanism (#2408)

Co-authored-by: Richard Schreiber <schreiber@rami.io>

src/pretix/testutils/middleware.py

@@ -0,0 +1,58 @@
+#
+# This file is part of pretix (Community Edition).
+#
+# Copyright (C) 2014-2020 Raphael Michel and contributors
+# Copyright (C) 2020-2021 rami.io GmbH and contributors
+#
+# This program is free software: you can redistribute it and/or modify it under the terms of the GNU Affero General
+# Public License as published by the Free Software Foundation in version 3 of the License.
+#
+# ADDITIONAL TERMS APPLY: Pursuant to Section 7 of the GNU Affero General Public License, additional terms are
+# applicable granting you additional permissions and placing additional restrictions on your usage of this software.
+# Please refer to the pretix LICENSE file to obtain the full terms applicable to this work. If you did not receive
+# this file, see <https://pretix.eu/about/en/license>.
+#
+# This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied
+# warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Affero General Public License for more
+# details.
+#
+# You should have received a copy of the GNU Affero General Public License along with this program.  If not, see
+# <https://www.gnu.org/licenses/>.
+#
+import contextvars
+
+from django.conf import settings
+from django.db import connection
+
+debugflags_var = contextvars.ContextVar('debugflags', default=frozenset())
+
+
+class DebugFlagMiddleware:
+    def __init__(self, get_response):
+        self.get_response = get_response
+
+    def __call__(self, request):
+        if '_debug_flag' in request.GET:
+            debugflags_var.set(frozenset(request.GET.getlist('_debug_flag')))
+        else:
+            debugflags_var.set(frozenset())
+
+        if 'skip-csrf' in debugflags_var.get():
+            request.csrf_processing_done = True
+
+        if 'repeatable-read' in debugflags_var.get():
+            with connection.cursor() as cursor:
+                if 'postgresql' in settings.DATABASES['default']['ENGINE']:
+                    cursor.execute('SET SESSION CHARACTERISTICS AS TRANSACTION ISOLATION LEVEL REPEATABLE READ;')
+                elif 'mysql' in settings.DATABASES['default']['ENGINE']:
+                    cursor.execute('SET SESSION TRANSACTION ISOLATION LEVEL REPEATABLE READ;')
+
+        try:
+            return self.get_response(request)
+        finally:
+            if 'repeatable-read' in debugflags_var.get():
+                with connection.cursor() as cursor:
+                    if 'postgresql' in settings.DATABASES['default']['ENGINE']:
+                        cursor.execute('SET SESSION CHARACTERISTICS AS TRANSACTION ISOLATION LEVEL READ COMMITTED;')
+                    elif 'mysql' in settings.DATABASES['default']['ENGINE']:
+                        cursor.execute('SET SESSION TRANSACTION ISOLATION LEVEL READ COMMITTED;')