Hey Shivaram, just to be clear, we don't usually expect applications to import spark.Logging. However it's true that this is a public API right now. Not sure whether that's a good idea.

Anyway, this method is supposed to be called as the first thing in the first thread that uses Spark. It's okay if it gets called again later in the program, but it's not okay if two threads call it concurrently. It may be possible to get rid of it with some locking in log(), but this could slow down applications slightly.