public AddressIterator getExternalEntryIterator() {
		lock.acquire();
		try {
			RefList refList = getFromRefs(Address.EXT_FROM_ADDRESS);
			if (refList != null) {
				return new ExtEntryAddressIterator(refList.getRefs());
			}
		}
		catch (IOException e) {
			program.dbError(e);
		}
		finally {
			lock.release();
		}
		return new EmptyAddressIterator();
	}
Returns the reference level for the references to the given address
@param toAddr the address at which to find the highest reference level
Ghidra/Framework/SoftwareModeling/src/main/java/ghidra/program/database/references/ReferenceDBManager.java