"Real-time doesn't mean that performance is as high as possible"

At one time "real-time" actually meant "real-time" as in "the sensor that determines whether to deploy the air bag in your car makes its decision in less than a ten thousandth of a second."

Nowadays, people are using "real-time" to refer to things that don't come close to being real time. If you allow a single thread to block all other threads than a thread engaging in a slow I/O operation could potentially block your whole app for several seconds. If that is the new definition of "real-time" than the phrase has become meaningless.