add a lock table for deadlock detection
	- simple hashing
	- realistic concurrency limits should be covered using a constant number of actual locks
		- middle ground between global lock and fine grained locks
	- write metadata about locker into lock file
	- finite set of locks to iterate through and work out deadlocks for
		- look at BDB deadlock detection modes
			- does it trigger on any block? after some fudge?
	- actual lock table
		- PerlIO :mmap?
		- updated based on actual locks being granted
			- seek to lock hash offset
			- write PID
			- could lock regions of this file using fcntl
