This MR introduces the following changes to the way operations lock
resources:

1. Introduces a parent-child relationship between operations where a
   "child" operation that is being run by its "parent" can share
   resource locks with the parent.

2. In the event that an operation cannot acquire ALL of its required
   resource locks, it will release any resource locks it did
   successfully acquire and then retry later. This gives each thread
   that is currently attempting to acquire resource locks a chance to
   do so.