QUuid::createUuid() is not reseeded when called from multiple threads

QUuid::createUuid() only seeds the random number generator the first time it is called, and thus all subsequent calls from a particular thread use the same seed. Thus, QUuid::createUuid() always generates the same sequence of numbers for each calling thread, just as qrand() does.

The class is indeed documented to be only re-entrant, but this static function should be made thread-safe.