Some hgweb commands accept a "revcount" parameter to indicate the amount of changesets to show per page. The value in this parameter is expected to be an integer. But if the value cannot be parsed, the exception is not handled properly and the response does not finish until the server timeout is enforced (which may be infinite).
Fixed by http://selenic.com/repo/hg/rev/77acd8ce01ce Isaac Jurado <diptongo@gmail.com> hgweb: ignore non numeric "revcount" parameter values (issue4091) (please test the fix)