lock manager app updates

apps/lock_manager/managers.py

@@ -0,0 +1,52 @@
+try:
+    from psycopg2 import OperationalError
+except ImportError:
+    class OperationalError(Exception):
+        pass
+
+import datetime
+
+from django.db.utils import DatabaseError
+from django.db.utils import IntegrityError
+from django.db import transaction
+from django.db import models
+
+from lock_manager.exceptions import LockError
+
+
+class LockManager(models.Manager):
+    @transaction.commit_manually
+    def acquire_lock(self, name, timeout=None):
+        lock = self.model(name=name, timeout=timeout)
+        try:
+            lock.save(force_insert=True)
+        except IntegrityError:
+            transaction.rollback()
+            # There is already an existing lock
+            # Check it's expiration date and if expired, delete it and 
+            # create it again
+            lock = self.model.objects.get(name=name)
+            transaction.rollback()
+
+            if datetime.datetime.now() > lock.creation_datetime + datetime.timedelta(seconds=lock.timeout):
+                self.release_lock(name)
+                lock.timeout=timeout
+                lock.save()
+                transaction.commit()
+            else:
+                raise LockError('Unable to acquire lock')
+        except DatabaseError:
+            transaction.rollback()
+            # Special case for ./manage.py syncdb
+        except (OperationalError, ImproperlyConfigured):
+            transaction.rollback()
+            # Special for DjangoZoom, which executes collectstatic media
+            # doing syncdb and creating the database tables
+        else:
+            transaction.commit()
+        
+    @transaction.commit_manually
+    def release_lock(self, name):
+        lock = self.model.objects.get(name=name)
+        lock.delete()
+        transaction.commit()