drjdpowell

I may not understand the architecture in question. As I understand it, if you have a subVI Front Panel in a subpanel of the main VI, then clicks on that (sub)Front Panel trigger events in the subVI’s event structure. And Alex is going to communicate this to the main VI via a queue, with the main VI talking back via a User Event. Should all work fine.

Which events don’t work in subpanels?

You’re not going to get much argument Alex. I’m the one advocating QSMs, yet I’m strongly against the common single-queue designs where user input can interfere with an executing macro (in the JKI template, for example, the Event structure is only run in the “idle” case, which executes only when the internal sequencing queue is empty). I don’t even like macros potentially interfering with each other by enqueuing on the back.

I think I should restate how I use the JKI. Mostly I use it for something that either is a UI or incorporates the UI. I use the cases of the case structure not to replace subVIs in general, but instead: 1) code closely related to the UI (where with a case one can use terminals and locals, and one can find the property nodes from the front-panel control right-click menu). 2) high-level code that if in a subVI would be a method of the “clustersaurus” cluster/object and would mainly be called in a simple chain connected by the clustersaur. Calling these instead as a “macro” doesn’t really lose any clarity. At finer levels of abstraction I use subVIs (basically, once I’m writing methods on components of the clustersaur). I do not, thus, "break down each function into small pieces to improve reusability”, at least not with cases. Your complex, enqueue-at-back example strikes me as something that should really be handled at this level (as a single case or clustersaur method). Or simplified, such as by subsuming both C and D under B (so B enqueues in front either C or CD). I am not an advocate of very complex branching logic in the QSM. As I use cases as an alternate to (some) subVIs, I tend to use them like subVIs in that one subVI can “contain” another subVI call. By enqueuing on front, and not having external writers to the internal queue, I can mentally abstract “macros” as unified operations independent of other macros (example: “Macro: refresh main table” refreshes the main display table, it doesn’t depend on what I enqueue after it). Using a single queue for both internal sequencing and inter-loop communication is a major flaw, IMO. All “QSM”s should use two queues. — James

Sorry, I didn’t understand this comment. It’s easy to make a multi-loop with a function sequence independent of the inter-loop message queue. I agree. I realized my mistake there and edited my post. I was thinking more about code clarity. Do it the clear and simple way and reserve the arbitrary sequence for when it is really necessary. They’re not rules, there guidelines. And they aren’t complete. Sorry, I realize I wasn’t really meeting your challenge. “Abort” does involve manipulation of the queue (partial flush) that would be against the normal “rules”. No enqueuing on the end, though. Is this kind of thing common? Why can’t D happen right after B? Why does C have to happen in between? And why can’t E happen after C? Even if you did this in subVIs it would seem a bit strange to me. Though certainly far clearer in subVis. Gotta go... — James

Like the simple rules; don’t like the difficult one. And the simple rules are followed by the JKI template. (2) is absolute because the message “queue” in the JKI is an event registration and you can only add to the end of the queue. (1) can be broken with Value(signaling) nodes and User Events (I sometimes use the first to initialize the UI) but it is easy to follow with the JKI. The simple rules can be followed with the JKI because it uses a separate queue for internal “operations”. This has different rules: 1. Only write from one process (enforced in the JKI by using a by-value queue implementation). 2. Always put items on the front of the queue. However, these rules aren’t the one I was talking about, as they CAN be built into a good “QSM” design. And should be. Like the JKI. [Edit: actually, JKI doesn’t enforce or guide one to put items only on the front of the internal queue. Wish it did.] — James

To me the evils are in the opposite order. Having the case-structure cases all correspond to atomic operations is certainly nice, but I really don’t like copying the UI update code. I don’t particularly like doing UI work by property nodes in subVI either (I like to be able to find the property nodes by right-clicking on the control, or vis versa). BTW, looking at the “Track History” VI does make me admit something: QSMs give you enough rope to hang yourself. QSMs give you a lot of flexibility; they don’t force you to follow narrow rules. But this doesn’t mean you shouldn’t be following the rules! Most of the time at least. And if you don’t know what the rules are then the QSM structure isn’t really going the guide you to them. So I would advise anyone using QSMs to understand the good arguments against them, not necessarily to stop using them, but to understand the rules, which you need to understand to use QSMs effectively.

Serial devices can be quite slow, so you have probably flushed the buffers long before the device sends back its response (including the echoed command). Since you know what the command string was, you can easily strip it off the front of the response.

I just don’t see it. The 5 subVIs chained on some clustersaurous object doesn’t seem that clearer than a JKI macro: SimulateReactor NormalOperatingModel InstabilityModel ReadReactorTemp IsTempOverLimit? And reordering the sequence or adding/removing actions is very fast with a macro. Ah, yes, the ability to connect directly to UI indicators and locals is one of the reasons I like using the JKI cases instead of subVIs for the high-level code that interfaces with the UI. But often times a particular UI update needs to be triggered by more than one action; in your design your updates only happen in one message case. — James Events are more complicated than a simple queue. But not necessarily more complex than a structure you might use instead. Note that if you have a separate loop for UI events that send messages by queue to your main message handler, then you have the exact same ordering issue in the link you gave above (i.e. you could fire a value change event, then enqueue a message, and the order of arrival at the message handler is indeterminate. I use one Queue (or User Event) per receiving process and to get One-to-Many I have the senders maintain an array of the receivers’ Queues. A difference with this from User Events is that instead of the sender needing to pass the User Event to the receiver in order to set things up, the receiver has to get it’s queue reference passed to the sender (in a “registration” message).

I mostly use subVIs for lower-level operations, with cases for the high-level operations. At the high level I don’t find any advantage to subVIs; a “macro” of JKI commands just becomes a long chain of subVIs. The cases have no reusability like a subVI, but the higher level is application-specific so that doesn’t matter. It is perhaps way too easy to carry on using cases down into the low-level operations that really should be subVIs. I did make that mistake at first. I’m not sure Events are actually quirky, rather than just people mistakenly using the same event registration in more than one event structure. I use the JKI and Events with VIs that have a UI. I tend to use queues for non-UI loops (I assume they have less overhead). And I tend not to use Events as broadcast or one-to-many communication methods.

Years ago I implemented the algorithm from this link. It’s not that hard to write in LabVIEW. It’s my oldest bit of code still in use (and I would be embarrassed to post it), but I’ve found it very reliable. — James

The JKI template follows (or at least allows one to follow) those three good rules. It has one message receiving system and has no need to send messages to itself nor have messages that must be executed in a specific order. It does this by keeping a separate, internal-only, by-value queue for actual operations (actually a string). This makes it a lot better than many/most “QSM” designs.

Are you aware of the “Measurement and Automation Explorer” or “MAX”? This is a NI application that should install with LabVIEW (I think it should exist on Mac OSX versions). It is used to set up “Tasks” that can be called within LabVIEW (and as asbo points out, there should be examples to help you at that point).

Only last week I had to diagnose a problem with one of these units in a new application, and the problem was they didn’t read the manual before wiring it up for 5VDC output (it’s TTL current-sink and they wired it as current-source). So I can’t really tell what kind of help the OP needs.

By reading the manual and trying it out. At least until you can come up with a more specific question.

My biggest suggestion is to use the JKI template as is. It’s a tested and well-thought-out design. If you need a second process, you can use another JKI SM or a simpler queue-run process. As to your current design: 1) as Daklu mentioned, don’t have two different receiving mechanisms in the same loop; use a User Event to communicate through the event structure. 2) A subtler flaw is that the loops use the same queue for internal operations and for receiving messages from external processes. This can lead to race-condition bugs as various processes queue up sets of messages at the same time. The JKI template uses a separate queue (actually a string) for internal operations. — James Oh, and instead of the functional global, consider using a “Message” system like Daklu’s Lapdog package for getting data between loops.

Are you planning on using an Xcontrol? The thing I’ve done that is most similar (I think) to what you are doing is an Xcontrol that allows the User to configure a list of “Actions” that they want the equipment to perform. The “actions” were an array of objects that were the datatype of the Xcontrol. The Xcontrol, containing a Table rather than a Listbox, allowed the user to configure each action via direct data entry or User menus. I’ll attach it in case it gives you any useful ideas. Note that it was never really polished or tested as the project it was for was discontinued. Probably not commented either. Oh, and working with Xcontrols can be a pain. — James ProfileTable.zip

My first thought is that a listbox is just a UI element for display purposes, and your real classes are “Users” and “Test Info”, which don’t had any obvious reason to inherit from the same parent class. Design them that way, and include a method in each called “Listbox Entries” that returns the necessary info to fill a listbox.

There are a few LabVIEW examples that might help, including “DateServerUsingStartAsynchronousCall.vi” that shows how to pass off new connections to a dynamically launched VI as ned mentioned.

I had wondered about that, once I understood interfaces to have strict rules about private data, as one can’t make an interface the descendant of any class that has any private data. Oh, it was just an idea I threw together in response to this conversation. Anyway, criticism is better than apathy.

Thanks Daklu, that helps me understand “Interfaces” better. I hadn’t appreciated the fact that interfaces should have no private data themselves, and I see now how your implementation can work with by-value objects (I suggest adding a by-value example if you ever have the time). My design above was motivated by what I perceived as a desire to create some kind of combined object that can simultaneously belong to two independent inheritance trees (complete with the private data of both trees).

Depends how many default values you have. If you’re carrying along a dozen constants you’ll have complex “Create” methods and generic probes which are well nigh unreadable. Note that a custom probe can call the classes methods in order to display the values. I usually put a method called “Text description” in any class hierarchy that gives a clear-english description of only the important information of the object; this makes making custom probes or other debug or logging tools easier. Yes. And that method will work with parameters that don’t have non-physical values (like −1 wheels).

As a different take on it, if “Number of Wheels” is a constant of the class (2 for Motorbike, etc.) then it shouldn’t be a “data” item at all. It should be an overridable method that returns the constant value: Car.lvclass would have a similar override with the constant 4. Use this method wherever you need the number of wheels. — James Added later: if the number of wheels isn’t a constant, you can still have different defaults. Make the default number of wheels “-1”, and have the methods return the default value for the class only if the data item is “-1”. That way you can change the value if you want, but the default exists without needing an “Init” method.

Hi Daklu, What do you think of my collection-of-objects-that-can-switch-between-type-identities idea posted above?

There was a big discussion about this on the 2012 Beta forum at NI.com, with a very strong recommendation from most beta testers that conditional indexing behave like regular indexing. I guess it was too late to make the change for 2012.