the GCompareDataFunc is used to sort queue. This function is passed two elements of the queue. The function should return 0 if they are equal, a negative value if the first element should be higher in the queue or a positive value if the first element should be lower in the queue than the second element.
user data passed to func
Sorts queue using func. This function will lock queue before it sorts the queue and unlock it when it is finished. If you were sorting a list of priority numbers to make sure the Since 2.10