By Marko Hakkarainen
I had some time to learn about new interfaces and finally I could implement my collection class as I had envisioned. I didn’t want to use iterable and iterator names, because I thought that would have been too bold a claim.
The original version of the collection class was (and is) used as a collection of sequence steps. Each element can be either a sequence command (send message, wait timer, wait complete etc.) or another collection of commands (sub-sequence). That’s the reasons for the labels and search method. Otherwise it is just a fancy (Rube Goldberg) array.
Next method is recursive and it steps through all elements in the collection. Execute is only method, which requires override.
For now, it’s at least an exercise in new interfaces. I don’t know if it’s useful enough to be in the code repository, but I can polish it up if needed.
Certified LabVIEW Architect
Iterable Collection LV2020.zip
I (re)watched James Powell's talk at GDevCon#2 about Application Design Around SQLite. I really like this idea as I have an application with lots of data (from serial devices and software configuration) that's all needed in several areas of the application (and external applications) and his talk was a 'light-bulb' moment where I thought I could have a centralized SQLite database that all the modules could access to select / update data.
He said the database could be the 'model' in the model-view-controller design pattern because the database is very fast. So you can collect data in one actor and publish it directly to the DB, and have another actor read the data directly from the DB, with a benefit of having another application being able to view the data.
Link to James' talk: https://www.youtube.com/watch?v=i4_l-UuWtPY&t=1241s)
I created a basic proof of concept which launches N-processes to generate-data (publish to database) and others to act as a UI (read data from database and update configuration settings in the DB (like set-point)). However after launching a couple of processes I ran into 'Database is locked (error 5) ', and I realized 2 things, SQLite databases aren't magically able to have n-concurrent readers/writers , and I'm not using them right...(I hope).
I've created a schematic (attached) to show what I did in the PoC (that was getting 'Database is locked (error 5)' errors).
I'm a solo-developer (and SQLite first-timer*) and would really appreciate it if someone could look over the schematic and give me guidance on how it should be done. There's a lot more to the actual application, but I think once I understand the limitations of the DB I'll be able to work with it.
*I've done SQL training courses.
In the actual application, the UI and business logic are on two completely separate branches (I only connected them to a single actor for the PoC)
Some general questions / thoughts I had:
Is the SQLite based application design something worth perusing / is it a sensible design choice? Instead of creating lots of tables (when I launch the actors) should I instead make separate databases? - to reduce the number of requests per DB? (I shouldn't think so... but worth asking) When generating data, I'm using UPDATE to change a single row in a table (current value), I'm then reading that single row in other areas of code. (Then if logging is needed, I create a trigger to copy the data to a separate table) Would it be better if I INSERT data and have the other modules read the max RowId for the current value and periodically delete rows? The more clones I had, the slower the UI seemed to update (should have been 10 times/second, but reduced to updating every 3 seconds). I was under the impression that you can do thousands of transactions per second, so I think I'm querying the DB inefficiently. The two main reasons why I like the database approach are:
External applications will need to 'tap-into' the data, if they could get to it via an SQL query - that would be ideal. Data-logging is a big part of the application. Any advice you can give would be much appreciated.
(I'm using quite a few reuse libraries so I can't easily share the code, however, if it would be beneficial, I could re-work the PoC to just use 'Core-LabVIEW' and James Powell's SQLite API)
I'm running into something I don't really understand. Maybe you can help me here !
I've got a LVLIB that is used as an 'Interface': it exposes public VIs which wrap around public functions of a private class (see code attached) . The class is private because I want to force the users to use the 'interface' functions.
In one of my interface VI, I create a DVR on the private class (Interface_init). The DVR is stored into a typedef (FClass_DVR.ctl) and this typedef is the 'reference' that link all the interface public functions.
In TestCode.vi (which is not part of the lvlib and illustrates the standard code that a user can create to use my driver), I can call my public interface functions and link them without any problem.
But as soon as I create an indicator on that reference (to create a state-machine-context-cluster for example), my TestCode VI breaks !
The error returned is : This VI cannot use the LabVIEW class control because of library access scope. The LabVIEW class is a private library item and can only be accessed from inside the same library or libraries contained in that library.
I understand that the class is private. But the DVR is contained into a public control. Using an In Place structure on that DVR into TestCode would not work, since the class is private. So why is the DVR control problematic at that point ? Creating it do not breaks any access protection...
Am I missing something ?
DVR Private POC.zip
I currently have a project that I am refactoring. There is a lot of coupling that is not sitting well with me due to typedefs belonging to a class, then getting bundled into another class which is then fired off as event data.
Effectively, I have class A with a public typedef, then class B contains ClassA.typedef and then class B gets fired off in an event to class C to be handled. Class C now has a dependency on class A which is causing a lot of coupling I don't want.
For my real world example I query a bunch of data from our MES, which results in a bunch of typedef controls on the connector panes of those VIs. Those typedefs belong to the MES class. I then want to bundle all that data into a TestConfig class and send that via an event to our Tester class. But, now our tester has a dependency on the MES.
I see a few ways to handle this. First is move the typedefs currently in the MES class, to the TestConfig class. The MES VIs will now have the typedefs from the TestConfig class on their connector panes, but at least the dependency is the correct "direction." Or, I can move the typedefs out of classes all together, but then I am not sure the best way to organize them. Looking for how others have handled these sorts of dependencies.