public void undo() {
		synchronized (this) {
			if (!canUndo()) {
				return;
			}
			try {
				dbHandle.undo();
				redoList.addLast(undoList.removeLast());
			}
			catch (IOException e) {
				dbError(e);
			}
		}
		invalidateCache();
		notifyRestored();
	}
Get the number of active datatype manager transactions
@return number of active datatype manager transactions
Ghidra/Framework/SoftwareModeling/src/main/java/ghidra/program/model/data/StandAloneDataTypeManager.java