public synchronized Set<T> getUnvisitedIndependentValues() {
		checkCycleState();
		visitedButNotDeletedCount += unvisitedIndependentSet.size();
		Set<T> returnCollection = unvisitedIndependentSet;
		unvisitedIndependentSet = createNodeSet();
		return returnCollection;
	}
Returns a set of all values that have no dependencies.  As values are removed from the
graph, dependencies will be removed and additional values will be eligible to be returned
by this method.  Once a value has been retrieved using this method, it will be considered
"visited" and future calls to this method will not include those values.  To continue
processing the values in the graph, all values return from this method should eventually
be deleted from the graph to "free up" other values.  NOTE: values retrieved by this method
will no longer be eligible for return by the pop() method. 

@return the set of values without dependencies that have never been returned by this method 
before.
Ghidra/Framework/Generic/src/main/java/ghidra/util/graph/AbstractDependencyGraph.java