Good example of livelock?

Question

I understand what livelock is, but I was wondering if anyone had a good code-based example of it? And by code-based, I do not mean \"two people trying to get p

Answer 1

A real (albeit without exact code) example is two competing processes live locking in an attempt to correct for a SQL server deadlock, with each process using the same wait-retry algorithm for retrying. While it's the luck of timing, I have seen this happen on separate machines with similar performance characteristics in response to a message added to an EMS topic (e.g. saving an update of a single object graph more than once), and not being able to control the lock order.

A good solution in this case would be to have competing consumers (prevent duplicate processing as high up in the chain as possible by partitioning the work on unrelated objects).

A less desirable (ok, dirty-hack) solution is to break the timing bad luck (kind of force differences in processing) in advance or break it after deadlock by using different algorithms or some element of randomness. This could still have issues because its possible the lock taking order is "sticky" for each process, and this takes a certain minimum of time not accounted for in the wait-retry.

Yet another solution (at least for SQL Server) is to try a different isolation level (e.g. snapshot).