Rolf Kalbermatter

I believe to have read somewhere that he eventually conceded that it was basically an unsolvable problem for a generic, easy to use solution. But that may be my mental interpretation of something he said in the past and he may not agree with that.

The popular serializer/deserializer problem. The serializer is never really the hard part (it can be laborious if you have to handle many data types but it's doable) but the deserializer gets almost always tricky. Every serious programmer gets into this problem at some point, and many spend countless hours to write the perfect serializer/deserializer library, only to abandon their own creation after a few attempts to shoehorn it into other applications. 🙂

Well the fact that you have VI Server property nodes in your top level VI should not force the entire VI hierarchy into the UI thread. Typically the VI will start in one of the other execution systems and context switch to the UI thread whenever it encounters such a property node. But the VISA nodes should still be executed within the execution system that the top level VI is assigned too. Of course if that VI has not been set to a specific execution system things can get a bit more complex. It may depend on how you start them up in that case.

Synchronous is not about running in the UI thread. It is about something different. LabVIEW supports so called cooperative multitasking since long before it also supported preemptive multithreading using the underlaying platform threading support. Basically that means that some nodes can be executed in Asynchronous operation. For instance any build in function with a timeout is usually asynchronous. Your Wait for Multiple ms timing node for instance is not hanging up the loop frame waiting for the expiration for that time. Instead it goes into an asynchronous operation setting up a callback (in reality it is based on occurrences internally) that gets triggered as soon as the timeout is expiring. The diagram is then completely free to use the CPU for anything else that may need attention, without even having to more or less frequently poll the timer to check if it has expired. For interfacing to external drivers this can be done too, if that driver has an asynchronous interface (The Windows API calls that Overlapping operation). This asynchronous interface can be based on callbacks, or on events or occurrences (the LabVIEW low level minimalistic form of events). NI VISA provides an asynchronous interface too, and what happens when you set a VISA node to be asynchronous is basically that it switches to call the asynchronous VISA API. In theory this allows for more efficient use of CPU resources since the node is not just locking up the LabVIEW thread. In practice, the asynchronous VISA API seems to be using internal polling to drive the asynchronous operation and that can actually cause more CPU usage rather than less. It should not affect the lifetime of a VISA session and definitely not the lifetime of a different VISA session. But disconnecting an instrument doesn't automatically make a session invalid. It simply causes any operation that is supposed to use the connection for actual transfer of bytes to fail.

A VISA Session is simply a LabVIEW refnum too, just a different flavor (sepcifically TagRefnum) which has an attached user readable string. Same about DAQmx sessions and any other purple wire. As such the "Is Not A Number/Path/Refnum" works on it too. One difference is that unlike any other LabVIEW refnum, you can actually configure if the lifetime of the VISA refnums should be tied to the top level VI or just left lingering forever until explicitly closed. This is a global setting in the LabVIEW options.

The straight-jacket should take care about shooting in your own feet, or actually shooting at all. 😁

Well, except that LLBs only have one hierarchy level and no possibility to make VIs private for external users. I do feel strongly about packed libraries being a potentially good idea with many limitations that I think were not fully thought out. - Version resource to have some control what version a packed library is? Tacked on by wrapping the proprietary archive format into a PE file and storing it as a custom resource in the PE file. And of course only under Windows, sorry Linux and Linux RT users, we forgot about you. - And the project environment is terrible in supporting them, as LabVIEW does not isolate packed libraries into their own application context. A PPL loaded into one application context, contaminates the entire LabVIEW memory space with its symbols and trying to load the same PPL but compiled for a different architecture into a different application context (RT target for instance) just messes up your project and sometimes beyond repair. And this is even so insane that if you load two projects separately at the same time with the same PPL with different architecture, you just managed to mess up both projects equally! Why does (almost) everything properly observe application context isolation except PPLs?

I didn't say they are a poor mans class, just that they are similar in several ways. 😁 The entire low level mechanics underneath are very similar, the interface provided to the user is somewhat different. Classes can have private data, libraries not. Libraries are the pre-request to creating packed libraries, or as you found out to use the 3rd party Activation Toolkit. They both have their use cases that are distinct from each other.

Have you used LabVIEW classes? A LabVIEW Library is in many ways similar except that you do not have methods and properties but simply only functions (a sort of method) in them, and yes of course no private class data. You can set functions to be private, public or community. Obviously there is no protected type function.

I can create it without problems in LabVIEW 2018 and 2020! So it is either that Scripting is not enabled in that LabVIEW installation or a bug in backsaving some of the scripting nodes to earlier LabVIEW versions. And I'm pretty sure that the Diagram property (called Block Diagram in the menu) is available since at least 2009 or thereabout. I can check this evening. My computer at work only has LabVIEW versions back to 2018 installed.

Top Level here almost certainly doesn't mean the diagram of the template VI. Instead LabVIEW distinguishes between a Top Level diagram which is basically the entire diagram window of a VI and sub diagrams such as each individual frame inside a case structure but also the diagram space inside a loop structure for instance. The tricky part may be that the diagram itself may indeed only exist once and remains the same even for clone VIs. The actual relevant part is the data space which is separate for each active clone (when you have shared clones) and unique for each clone (when you have pre-allocated clones).

Technically it is a resource collector, but not exactly in the same way typical garbage collectors work. Normal garbage collectors work in a way where the runtime system somehow tracks variables usage at runtime by monitoring when they get out of runtime scope and then attempts to deallocate any variable that is not a value type in terms of the stack space or scope space it consumes. The LabVIEW resource collector works in a slightly different way in that whenever a refnum gets created, it is registered together with the current top level VI in the call chain and a destroy callback with a refnum resource manager. When a top level VI stops executing, both by being aborted or simply executing its last diagram element, it informs the refnum resource manager that it goes idle, and that will then make the refnum resource manager scan its registered refnums to see if any is associated with that top level VI and if so, call its destroy callback. So while it is technically not a garbage collector in the exact same way as what Java or .Net does, it still is for most practical purposes a garbage collector. The difference is, that a refnum can be passed to other execution hierarchies through globals and similar and as such might still be used elsewhere, so technically isn't really garbage yet. There are three main solutions for this: 1) Don't create the refnum in an unrelated VI hierarchy to be passed to another hierarchy for use 2) If you do create it in one VI hierarchy for use in another, keep the initial hierarchy non-idle (running) until you do not need that refnum anymore anywhere. 3) If the refnum is a resource that can be named (eg. Queues, Notifiers) obtain a seperate refnum to the named resource in each hierarchy. The underlying object will stay alive for as long as at least one refnum is still valid. Each obtained refnum is an independent reference to the object and destroying one (implicit or explicit) won't destroy any of the other refnums.

That's my understanding yes. I have so far not upgraded to the library versions of the OpenG libraries, so do not have any long term experience with this. When I upgraded by accident one of the libraries I did see that it seemed to automatically relink callers, but that was not what I was prepared to deal with at that point as I was only making a minor edit to the project, so reverted to the previous OpenG version rather than committing the modified VIs to source code control.

The namespace of the subVIs themselves changes, so I'm afraid that separation of the compiled code alone is not enough. The linking information in the diagram heap has to be modified to record the new name which now includes the library namespace. As long as it is only a recompilation of the subVI, separation of compiled code in the caller indeed should not require a recompilation of the caller, but name changes of subVIs still do. In fact the automatic relinking from non-namespaced VIs to library namespaced VIs is a feature of the development environment but there is no similar automatic reversal of this change.

Did you run into any specific problems in that respect? If those commercial libraries are provided with diagram, even if they are password protected or hidden behind a license, they should load and recompile fine. If the library is not provided with diagram, it is pretty much useless anyways, as you can not change LabVIEW versions at all. What problems have you seen? What LabVIEW versions? Or is this more an academic exercise to complain about something? I don't endorse the libraryfication of existing libraries just for the sake of making them a vilib. But it can be useful when trying to do componentized deployment through packed libraries. But your argument kind of sounds like a constructed argument, unless there is a specific problem that I'm not aware of.