Handling race condition in model.save()

Question

How should one handle a possible race condition in a model\'s save() method?

For example, the following example implements a model with an ordered list

Answer 1

I use Shawn Chin's solution and it proves very useful. The only change I did was to replace the

self.position = self.parent.item_count

with

self.position = self.parent.latest('position').position

just to make sure I am dealing with the latest position number (which in my case might not be item_count because of some reserved unused positions)