Ask HN: How do you stay fresh on the basics of computer science?

I had an uncomfortable experience last week where I realized I'd forgotten the basics of condition variables (in particular, how to prevent the thundering herd problem). The week before, I had the problem of working out CIDR from first principles and made some basic mistakes before I got it right. I would like to refresh my basic knowlesdge periodically to keep things current and accessible, does anyone here do this and if so how do you do it? Do you retake courses? Do you reread textbooks? In your opinion is it worth spending the time to do this? I'd be relearning and refreshing 3 out of 4 years of my undegraduate course over the course of a year.