[TACHYON-220] WIP Comments describing issues and possible solutions 

Some initial comments to help improve the performance of master info. From what I gather there is locking on stack local objects that are never really put back into the map. I would appreciate suggestions before implementing it, hence the WIP tag.
"That's the point ,whey are we sync'ing to update inode and do all sorts of operations blocking the thread when it is on the stack and not shared between threads"

The map is not mutated but the value is. That implies that the value is also protected by this lock. So you still need to sync even with concurrent map.

"If the map is concurrent we can do whatever we like to inode and only need sync when we put it back in to the shared map."

As stated above, the reference points to memory that is shared between threads. You need to make the value immutable (can't update memory) or do a lock. I tend to prefer immutable over locking in this context