Lock for key ranges instead of entire DB

Can we lock a key range in a DB while still allow clients operate on the other key ranges?

Two scenarios can benefit from this:
1) If data corruption happens at a small key range, say [b, c), the cluster can still serve traffic in the rest of key space, while we are restoring the data in [b, c).

2) If someone wants to move data in a small key range, say [b, c), from a live cluster A to another live cluster B, we can only lock that key range while still allow both clusters to serve traffic to the rest of key space.

The implementation is similar to Issue https://github.com/apple/foundationdb/issues/1044, except that we don't have to distinguish read and write lock.