drjdpowell

I don't think you give that impression. It's not even close to complete (the four-hour time limit would be a killer), but I can show the statemachine with a case that is; the "Main Menu" when the user selects the "Fast Cash $50" option (see attachment). I found the ATM problem to be obviously calling for a state machine; it practically defines all the states for you. The problem equally seems to call for some LVOOP, again practically defining all the classes: "User Console" and "Account Database", with children "Simulated Console" and "Simulated Database" (ready for the eventual replacement with "Physical Console" and "Enterprise Database"). If I were to use a JKI-SM (though I wouldn't be allowed the template on the exam), I might instead have had "Macros" such as... "// Main Menu Card Slot >> disable Keypad >> disable Menu State >> Main Display Message >> Main Menu Wait for User Input Process Main Menu Input" ... with the "Process Main Menu Input" calling (if the User pushed this button) "Fast Cash $50", which would call "Withdrawal >> Complete". The QSM version would not be terrible but would be clearly poorer than a true SM. But this problem is very clearly definable as a statemachine. Most programs I write involve "do the task requested before returning to idle", with the complexity of the task being more easily broken down into sub-tasks than states. For complex tasks, JKI-style macros are quite clear and they're quick to write compared to wiring up subVIs. The subVI option is clearer than JKI-SM frames, and I can appreciate some of the other advantages you point out, but the real reasons I've started to use subVI's more and more lately is the advantages of OOP classes and dynamic dispatch. BTW, what do you think of the provided example solution to the ATM example test? The one where it's done with Action Engines. -- James

Sorry, should have used a smilie of some kind. Not an effective smilie user. There. On a side note, I have just learned that there is a practice CLA exam and tried a go of it last night. Being an ATM program with obvious state-fullness I used a state machine, my first real one ever, I think! -- James

Hi Daklu, Another of the problems with the bad "QSM" name is that there are many conversations where someone brings up "QSM" and it triggers comment about their flaws as true state machines, "state diagrams" and such, WITHOUT ascertaining if the original use of the QSM pattern was anything to do with "different responses to the same message depending its current state". I suspect most use (and certainly better use) is more similar to what you use your message handler for. It may even be intended (dare I say it) as a structure for programing without separating the UI from the rest of the code! We lesser programmers tend to do that. So I did get the mistaken impression that people were suggesting true state machines for all sorts of purposes that seemed to me to be a poor fit. You might be right. I think (lest I'm mistaken) that a QSM like JKI's is interchangeable with a QMH with appropriate subVIs (and the JKI-SM can meet your three conditions for QMHs). In my own use of the JKI-SM, my first uses definitely were flawed by too little use of subVI's, while lately I use a mix of mostly subVIs for low-level operations and frames of the case structure for higher-level ones. Your argument that case structures, loops and subVI's is clearer than a queue for complex processes is a much better one than your state-machine related criticisms; now your talking about what people use "QSMs" for. -- James

You could also consider using a multi-column listbox and right-click menu, customizing the menu to the set of options available for the specific box right-clicked on, then write the selected option into the box.

Hi Daklu, Most of your criticism of the (badly named) "QSM" is all down to the flawed design of using the same queue for messages to the QSM and "states" (really operations) within the QSM. This flaw may be common, but it is not inherent to QSMs, and templates such as the "JKI statemachine" don't have it. There is no asynchronicity in a properly designed QSM (your point 4), nor do producer loops directly initiate QSM "states" (point 1). As to better separation of the UI (point 3), I'm not sure ignoring messages is all that great an idea (I have visions of the annoyance my Users will have after pressing "start", and coming back 5 hours later to find the equipment just sitting there). Point 2 is complicated since a QSM isn't actually a state machine and thus isn't a good way to implement a complex state diagram. But how good is a true state machine at implementing a complex flow chart? Aren't you making the same error as "QSM for everything" people by suggesting "true state machine for everything"? Is a hammer a useless tool just because people have mislabeled it as a type of saw? -- James

The flowchart tends to seem more intuitive to me for what I'm doing, so the badly-named QSM is good for me. Admittedly, this may be just a lack, on my part, of a clear understanding of the value of state diagrams. -- James

Only thoughts: -- I would separate the changing of frames of reference (AB in A-frame --> AB in B-frame) from the inverting of the vector (since the later is then trivial) -- shouldn't the change of reference frame involve two relative angles? rather that the single angle your code snippet seems to have? -- James

That is a flawed design, due to the use of the same queue for both internal operations of the lower loop and incoming messages from the event structure in the upper loop, leading to indeterminacy in the order of operations. Good design always uses separate queues. I, personally, would recommend anyone starting to use "QSMs" (how about "Queued Operation Machines", QOM?) to use a good template such as the JKI statemachine toolkit to avoid these types of design mistakes (which I sadly recall making myself). -- James

For the benefit of Dannyt and others reading, "Queued State Machines" such as the JKI state machine are misnamed in that they are not actually state machines. True state machines are a different concept, and are what Paul_at_Lowell and Daklu are talking about. QSMs are more like queued command or queued operation machines, and thus the concept of a "macro" set of commands applies. -- James