Add mutex to page tree move function, fix #1518

* Use django-db-mutex module to implement a mutex that allows only
  one page tree move operation at a time.

CHANGELOG.md

@@ -6,6 +6,7 @@ UNRELEASED
 * [ [#1989](https://github.com/digitalfabrik/integreat-cms/issues/1989) ] Improve load time of locations endpoint
 * [ [#1578](https://github.com/digitalfabrik/integreat-cms/issues/1578) ] Add option to hide files in global media library
 * [ [#1752](https://github.com/digitalfabrik/integreat-cms/issues/1752) ] Show chapter for internal link suggestions
+* [ [#1518](https://github.com/digitalfabrik/integreat-cms/issues/1518) ] Prevent database corruption when moving 2 pages at the same time
 
 
 2023.2.0

Pipfile

@@ -29,6 +29,7 @@ twine = "*"
 
 [packages]
 integreat-cms = {editable = true, path = "."}
+django-db-mutex = "*"
 
 [requires]
 python_version = "3.9"

integreat_cms/cms/models/abstract_tree_node.py

@@ -8,6 +8,9 @@
 from treebeard.exceptions import InvalidPosition
 from treebeard.ns_tree import NS_Node
 
+from db_mutex import DBMutexError, DBMutexTimeoutError
+from db_mutex.db_mutex import db_mutex
+
 from .abstract_base_model import AbstractBaseModel
 from ..constants import position
 
@@ -259,6 +262,8 @@ def move(self, target, pos=None):
         :type pos: str
 
         :raises ~treebeard.exceptions.InvalidPosition: If the node is moved to another region
+        :raises db_mutex.DBMutexError: If the DB mutex could not be retrieved
+        :raises db_mutex.DBMutexTimeoutError: If waiting for the DB mutex timed out
         """
         logger.debug("Moving %r to position %r of %r", self, pos, target)
         # Do not allow to move a node outside its region
@@ -282,7 +287,21 @@ def move(self, target, pos=None):
         # Moving a node can modify all other nodes via raw sql queries (which are not recognized by cachalot),
         # so we have to invalidate the whole model manually.
         invalidate_model(self.__class__)
-        super().move(target=target, pos=pos)
+        try:
+            with db_mutex(f"tree-page-{self.region}"):
+                super().move(target, pos)
+        except DBMutexError as e:
+            logger.error("Could not retrieve database mutex to save %s", self)
+            raise DBMutexError(
+                # pylint: disable=consider-using-f-string
+                _('Could not change position in tree of "{}".'.format(self))
+            ) from e
+        except DBMutexTimeoutError as e:
+            logger.error("Retrieving database mutex timed out while saving %s", self)
+            raise DBMutexTimeoutError(
+                # pylint: disable=consider-using-f-string
+                _('Could not change position in tree of "{}".'.format(self))
+            ) from e
         invalidate_model(self.__class__)
 
         # Reload 'self' because lft/rgt may have changed

integreat_cms/core/settings.py

@@ -247,6 +247,7 @@
     "django.contrib.staticfiles",
     # Installed third-party-apps
     "corsheaders",
+    "db_mutex",
     "linkcheck",
     "polymorphic",
     "rules.apps.AutodiscoverRulesConfig",
@@ -1012,3 +1013,11 @@
 
 #: The URL path where XLIFF files are served for download
 XLIFF_URL = "/xliff/"
+
+
+############
+# DB Mutex #
+############
+
+# Our database operations should never exceed 60 seconds
+DB_MUTEX_TTL_SECONDS = 60

integreat_cms/locale/de/LC_MESSAGES/django.po

@@ -2340,6 +2340,10 @@ msgid "The node \"{}\" in region \"{}\" cannot be moved to \"{}\"."
 msgstr ""
 "Der Knoten \"{}\" in Region \"{}\" kann nicht nach \"{}\" verschoben werden."
 
+#: cms/models/abstract_tree_node.py
+msgid "Could not change position in tree of \"{}\"."
+msgstr "Position von \"{}\" im Baum konnte nicht geändert werden."
+
 #: cms/models/chat/chat_message.py
 msgid "sender"
 msgstr "Absender:in"

sphinx/conf.py

@@ -135,6 +135,9 @@
     ("py:class", "builtins.AssertionError"),
     ("py:class", "builtins.int"),
     ("py:class", "NoneType"),
+    ("py:class", "db_mutex"),
+    ("py:attr", "db_mutex.DBMutexTimeoutError"),
+    ("py:attr", "db_mutex.DBMutexError"),
     ("py:class", "django.contrib.admin.helpers.ActionForm"),
     ("py:class", "django.contrib.admin.checks.ModelAdminChecks"),
     ("py:attr", "django.contrib.auth.models.Permission.user_set"),