I was waiting on line for a soda at Radio City Music Hall just before the premiere of “Live Free or Die Hard” a couple of weeks ago when I realized the guy standing in line ahead of me was actor Sam Rockwell, who I interviewed a few years ago. Nobody else recognized Rockwell, though several people mistook my daughter Xan’s boyfriend Randy, who was standing next to me, for Ashton Kutcher. Even indie stalwart Rockwell’s more mainstream films like George Clooney’s criminally underrated directing debut “Confessions of a Dangerous Mind” (in which Rockwell played game show host and alleged CIA agent Chuck Barris) and Ridley Scott’s “Matchstick Men” (Sam was Nicolas Cage’s con-man partner) didn’t exactly play to huge audiences. Now the very talented Rockwell, a specialist in marginal characters, takes a rare stab at playing a relatively normal person, a Manhattan stockbroker, in the psychological thriller “Joshua,” which I give three stars to today in The Post.