func for each element in the queue passing
user_data to the function.
It is safe for
func to remove the element from
queue, but it must
not modify any part of the queue after that element.
Available since: 2.4
This method is not directly available to language bindings.
The function to call for each element’s data.
User data to pass to
The argument can be
The data is owned by the caller of the method.