- Removed support for Python 2.x and Django 1.x
Added a unique index on the key column in the Lock model.
The Lock model does not have a distinct key on the key column. DatabaseLock relies on get_or_create to try to acquire a lock if one does not exist.
Unfortunately, get_or_create is not thread-safe. It is an illusion that can fail when called at the same time from different threads/servers. Consider two servers trying to acquire a DatabaseLock on key sellBrooklynBridge. Consider the following sequence of events:
- Server A calls django.db.models.query.py:464: return self.get(**lookup), False. No sellBrooklynBridge is in the DB, so the get fails with a DoesNotExist.
- Server B calls django.db.models.query.py:464: return self.get(**lookup), False. No sellBrooklynBridge is in the DB, so the get fails with a DoesNotExist.
- Server A creates the Lock DB row with the sellBrooklynBridge key
- Server B creates the Lock DB rowwith the sellBrooklynBridge key
Result: the Brooklyn bridge got sold twice.
The way to solve this is to add a unique index on the key column in the Lock model. Then, wrap lock, created = Lock.objects.get_or_create(key=self.key) in an exception block and catch integrity errors.
This could break systems that are used to the faulty mechanism.
- koliber
- Changed some confusing/noisy log messages [hexsprite]
- Initial release