I'm looking for matchmaking algorithm for 1x1 online game. Players must be matched not by their skill or level, as usual, but by some specific filters. Each player sends request, where he specifies some set of parameters (generally, 2-4 parameters). If some parameter is specified, player can be matched only with those who has sent this parameter with exactly the same value, or those who hasn't specified this parameter.

I need this algorithm to be thread-safe and preferably fast. It would be great if it'll work for 3-4 or even more parameters, but also I'm looking for algorithm that works with only one parameter (in my case it's game bet). Also I'd appreciate ideas on how to implement or improve this algorithm on my server platform - ASP.NET.

One more problem I'm facing is that finding match can't be executed right after user sends request, because if other user sends request before matching for previous is finished, they won't be matched even is they possibly could. So it seems that match finding should be started on schedule, and I need help on how to optimize it and how to choose time interval for starting new match finding.

P.S. I've also posted this question on stackoverflow