I have a feeling this is a wrapper around a POSIX-style
select call, or something similar in nature, that's used to efficiently poll multiple handles for data that can be read.
select-driven code is deemed to be "polling" when it checks for data ready to be read or handles ready to be written to.
It's unlikely that most programmers have ever used this function. It has very narrow use cases, you must be juggling a non-trivial number of MySQL handles at once. Most applications use a handful, and often with a connection pool.