Add object locking around updates + deletes

[cbeer]

Or maybe there's something else in the architecture that's stopping simultaneous updates?

[justinlittman]

Will second attempt to lock block or raise? (I don't love blocking, as it might lock up http requests. I'd prefer to see it raise so that the caller can retry.)

[cbeer]

We can make it do whatever. It's not yet clear to me whether this is needed (but also not clear that it isn't.). What do you think?

[justinlittman]

In theory it shouldn't happen. However, since on the DSA side publishing is performed by a job, anything is possible given retries. This seems lightweight enough that it is worth it.