I'm not actually sure about this myself.

Currently when you close the MDCClosable it will remove the value from the MDC. The close method doesn't put things back to the way they were.

The put method called when MDCClosable is created returns void so this isn't a trivial thing to implement. I imagine that different logging providers might not return the old value like the put method on the map.

Should something like this be implemented?

By trivial I mean if we have to call get every time an MDCClosable is created there might be a performance impact or something.