ShaunR

Well. The title was really to place the discussion in the queue producer/consumer pattern vs a ring buffer producer/consumer. Whilst queues generally are just a buffer behind the scenes (some can be linked lists) there is a domain separation here. Queues are a "Many to One". Their real benefit is having many produces and a single consumer. In the one producer, one consumer, this is ok, but the example isn't really a one-to-one although we would shoehorns it into one in LabVIEW such that we have one consumer then branch the wire. Additionally. Looking at the classic dequeue with case statement which many messaging architectures are based on including mine. This is mitigating concurrency by enforcing serial execution. The Disruptor or ring buffer approach is a "One to Many". So it has more in common with Events than queues.Events, however, have a lot of signalling and, in labview, are useless for encapsulation. I've only breached the surface of the Disruptor pattern. But it doesn't seem to be a "Data Is Ready" approach since its premise is to try and remove signalling to enhance performance. The "Write" free wheels at the speed of the incoming data or until it reaches a piece of data that has not been "consumed". By consumed, I do not mean removed, simply that it has been read and therefore is no longer relevant. A "Reader" requests a piece of data that is next in the sequence and waits until it receives it. Once received, it then processes it and requests the next. So. If it is up to the latest, it will idle or yield until new data is incoming. The result seems to be self regulating throughput with back-pressure to the writer and all readers running flat out as long as there is data to process somewhere in the buffer. It also seems to be inherently cooperative towards resource allocation since the fast ones will yield (when they catch up to the writer) allowing more to the slower ones. Here's a pretty good comparison of the different methods. There's also a nice latency chart of the Java performance And finally. Some hand drawn pictures of the basics

It doesn't solve the garbage collection issues in Java. They "alleviate" that by having custom objects and reboot every 24hrs . The advantage of this technique is that M processes can work on the same data buffer in parallel without waiting for all processes to finish before moving to the next. As an example. Lets say we have a stream of doubles being written to a Queue/buffer of length N. We wish to do a mean and linear fit (Pt by Pt). We will assume that the linear fit~ 2x slower and that the queue/buffer is full and therefore blocking writes. With a queue we remove one element, then proceed to do our aforesaid operations (which in LabVIEW we can do in parallel anyway). The queue writer can now add an element. The mean finishes first and then the reader has to wait for the linear fit to finish before it can de-queue the next element. Once the linear fit finishes, we then de-queue the next and start the process again evaluating the mean and linear fit. From what I gather with this technique the following would happen. We read the first element and pass it to the mean and linear fit. The mean finishes and then moves on to the next data point (doesn't wait for the linear fit). Once the linear fit has finished, the next value in the buffer can be inserted and it too moves to the next value. At this point the mean is working on element 3 (it is twice as fast)The result is that the mean travels through the buffer ahead of the linear fit (since it is faster) and is not a consideration for reading the next element from the buffer. Additionally (the theory goes) that once the faster process has reached the end of the data, there are more processing cycles available to the linear fit so that *should* decrease its processing time. Now. They cite that by reading in this fashion, they can parallelise the processing. We already have that capability so I don't think we gain much of a benefit there. But leveraging processing of a function that would spend most of it's time doing nothing due to data being unavailable until the slower process finishes seems like it is worth experimenting with.

I happened to come stumble upon what, was to me, an interesting presentation about high speed transaction processing (LMAX presentation). Their premise was that queues, which are the standard approach, were not the most appropriate for high throughput due to the pipeline nature of queues. To achieve their requirements, they have approached it from using ring buffers which enable them to parallel process data in the ring buffer, thus alleviating, but not eliminating pipe-lining (if the readers are faster than the writer, they still have to wait for data). The "classic" producer consumer in LabVIEW heavily relies on queues and, one of the problems we encounter is when the reader is slower than the writer (we are concerning ourselves with a single write only). Because we can only process the data at the head of the queue, we have a similar throughput problem in that we cannot use LabVIEWs parallelism to alleviate the bottleneck. So I was thinking that the alternative design pattern.that they term the Disruptor might be worth discussing even though we are contained by how LabVIEW manages things in the background (it will probably pan out that LabVIEWs queues will out-perform anything we can write in LabVIEW-parallel or not). Thoughts? (apart from why can't I upload images )

Just append the SENDER (as received by the handler) as part of the ACK message

That's what the Just inspect the SENDER part of the message

The controls have different names from one picture to the other. They are the same controls, right?

Well. It looks like images aren't in the supported datatypes for that package

Well. It's fairly easy to eliminate if that is a suspected problem. Just put a check path exists and log the path before the dialogue is invoked. Then, if you see the dialogue again, you will be able to see whatf the path was and whether the app thinks it exists. You can them paste it into a browse window and see if explorer complains.

What is the default path or current path? Is it pointing to a networked drive? Are all drives actually available that are mapped? I've seen in windows (not specifically LabVIEW) that file dialogues can be "flakey" when network locations are invoked on drives that are unavailable or NAS locations that are asleep. Basically any network access failure will bring windows to it's knees and is usually facilitated by a file action (browse or open/save). When a file dialogue is invoked, it will try to enumerate drives and you only need one to not respond. If you look carefully, you will see that all the indicators are there, they are just not populated (they appear as "discolourations")-classic symptom of struggling to enumerate the drive list. You may find something in the windows event log.

Not from Europe (not sure about NK; cannot find any relevant EU sanctions) . Sanctions to Iran basically cover finance, transport and energy although if you had a "nuclear processing plant.vi", they might group that under "energy". LabVIEW is, apparently, also available in Iran, so I wouldn't be too quick to jump to conclusions about the OPs country of origin. Maybe it just cannot be bought online from wherever he resides. Congratulations! Lavag.org made it on the spooks radar. Three more keywords and they break your door down

Elimination of the case structure isn't that important. The encapsulation of the state-machine is the important bit which is what you have achieved but It is only the equivalent of "create Sub VI" on the case. From your description, you are still "driving" the machine with external, module specific messages which causes you to require the application state-machine (execution engine or sequencer) to know what module specific messages to send and in which order. That's a dependency that I don't like. So. Keep the class and keep the case structure and hard-code the "Message X" and "Message Y" in a couple of frames (probably multiple hard-coded messages in one frame) and we are back to the API. The execution engine only has to worry about application stuff and not what language the state-machines speaks (I just feel that if the messages are hard-coded, then there isn't any point to them). At that point, you can rationalise the interfaces to the modules (same messages) and swap entire modules in and out with the same execution engine (same as switching out the actor, I suppose) OR swap the execution engine with another. The end result of breaking message interdependence is is that you get swappable modules, swappable execution engines and swappable user interfaces and whole sections of a project become reusable (which is why I'd love to see the project manager cope with nested projects).

No. And I think this is where we view things fundamentally differently perhaps. In my world, messages have nothing to do with states. Well. That's not strictly true since there may be one or two out of 100 that you could identify as having a particular state. Perhaps it's better to say there is no inherent link between them. Messages are just commands and the handler is just the API interface to the state-machine - the contoller. There is no different messaging strategy "just" for state-machines where messages map to discrete states. States are handled by a separate process (the state-machine). In this world, the rest of the software doesn't care about all the internal states of the module let alone be responsible for driving them. Many of the messages I send to a state-machine are things like INIT, START, STOP, PAUSE, CONTINUE etc But if you change your terminology and say...... "Ahh... so if a message is handled the same way across multiple messages, you combine several messages into a single frame. Then yes. That was what I was stating in comparison to events.

You can already. It's called C++, C#, VB, Python or any other text language. Choose your poison.

Really? Hmmm. So as an example, you would use my #5 argument to suggest that requiring to be in a certain state to be able to dequeue a message at all, means that messaging and state have been separated and are not dependent?#2 is just adding multiple strings to a frame so it behaves similarly to adding multiple control events to a single event structure frame (same code, different messages).

You only really need to onion route when you traverse a boundary (like forwarding across TCPIP) so message depth is usually limited to 2 (arguably it could be considered chaining at that point). Everything else you send directly. If you were to onion route (i.e. concatenate) to twenty levels, then I can see that may be an issue.I just don't see the point if I can send directly. What's your use case?

Well. In context of my comments on the other thread. The message handler would always be the first example and all the state info and logic would be pushed down in the hierarchy.into subvis/classes (in your examples just "create subvifrom selection" and add the while loop memory for the state to it). A few of the arguments for #1 that I would put forward (not any particular order) 1. it is cleaner and easier to read.(subjective I know, but the frame represents messages only rather than a message and a state) 2. You can group messages in the frames (like you can with events) independently of state. 3. You can guarantee that a "dequeue" happens for every message regardless of state. 4. Less code replication. 5. Separation of responsibilities (bugs in the statemachine are separate from bugs in the message handler).

You need to call an initialising function first and it will return the reference that you can then pass to your other functions. Using the VISA example again, there is a viOpen function C Syntax ViStatus viOpen(ViSession sesn, ViRsrc rsrcName, ViAccessMode accessMode, ViUInt32 openTimeout, ViPSession vi) Visual Basic Syntax viOpen&(ByVal sesn&, ByVal rsrcName$, ByVal accessMode&,ByVal openTimeout&, vi&) It takes as an argument a string which is the resource name - rsrcName$ - (e.g. "Com1"). and returns the session value which is the vi&. It is the vi& that is passed to the other functions. Your DLL should have a similar function that takes a resource name string and passes back a LVRefNum which you can then pass into your other function calls.

Could be. Could also be a class, or action engine-depends on your level of abstraction. The goal is to have one VI per frame that is not dependent on the message order and is atomic. For a trivial example. You could have a JKI style statemachine set of messages for opening, reading and closing a file and have to pass the reference from frame-to-frame. I'm suggesting this is a bad idea and you should have a one read message and it invokes a READ vi which opens reads and closes the file.

Don't get me wrong. you can have stateful FUNCTIONS. I'm saying that the HANDLER should not be stateful. Sending a message should execute a function every time rather than conditionally executing if a message was received earlier....... there be monsters Nothing to stop you having a class in a frame that maintains its state but it should be encapsulated within the scope of the function, not the handler or, even better, just don't send a message at all (it depends what state we are talking about- file open, read,close........bury it in the function. Move slide if position is greater than 3mm, thats a sequencers job and it shouldn't send "move"). The TCPIP code I placed was just a quick and dirty way of sending commands. From experience it is quite adequate for the local loop at medium rates (10s of ms) or for an internal GB network of hundreds of ms, but forget it for internet or high speed comms. It is also useful if you are talking to many destinations with short packets infrequently (e.g. 50 cRIOs with "RESTART"). It is up to the developer to define the functions and features, the handler just provides a messaging interface. I think I said earlier that in the real world I use a comms handler and can send via a number of methods. That module actually maintains connections (whatever the interface) but I have made it function so that they die if not used for a couple of minutes so if they are used often they persist, but I don't have to explicitly close them. You can do whatever you like in the handlers, just KISS 1. Actually. The generic symantics are TARGET->SENDER->CMD->PAYLOAD. So no. It's not loose. Target and sender are purely for routing. It could have been Destination IP address and Source IP address but for this implementation I chose VI names and relieved the burden on the user of typing in the sender on every message. Additionally, you don't have to use queues. It's just convenient that queues can be isolated by names so the target is consumed for that purpose. Queues also break the need for wires running all over the place, or shared storage (which is required for events). You could have used TCPIP primitives in the Send instead of Queues and it would have worked much the same way directly over a network (which is pretty much how dispatcher in the CR works). In this respect it is a messaging strategy realised with queues and handlers. But the messaging itself would be identical with TCPIP listeners and opens. This is what makes it easy to traverse boundaries both in hardware and in software languages since it could be a webserver written in python at the other end (not easy to do with labview coded messages). 2. Well. You can't beat discipline into programmers. Only the army can do that But you have perhaps missed the "reuse" aspect. Once you have a TCPIP handler, for example, then why do you need to rename it? It's like renaming Lapdog. Besides renaming is just a search and replace string on all VIs. Not as if you have to go and rename a shedload of VIs,and have to re-link all over the place is it? 3. I don't understand the question. There is no TCPIP display loop. There is a TCPIP handler which happens to be showing its panel. And there is an IMG handler. The listener just forwards the message using Send.

I'm no expert in VB but looking at the VISA programming manual, references are usually passed as Byval Value& (notice the ampersand) e.g. C Syntax: ViStatus viGpibSendIFC(ViSession vi) Visual Basic Syntax: viGpibSendIFC&(ByVal vi&) The C pointer (asterisk) makes me tentative, however, since it could be a ByRef. But it is unusual. Hopefully Rolf will be along to answer definitely (he's the guru on this kind of stuff, I tend to work the other way around - Labview->C)

The non-labview thing I found interesting was that cats operate time-shares on their territory if they live closely packed together so they don't have to meet each other. If only I could get my neighbour to co-operate like that!

Not exactly what you are asking for but it may be suitable even if not perfect (case select-it uses the JKI plugin framework). Alternatively, it would be a very good starting point for your own framework plugin.

The vision toolkit is for, well, vision (images, OCR, camera feature detection.etc) I would take a look instead at the Robotics toolkit which has path planning, obstacle avoidance, directed graphs etc.

The IMAQ Spoke might be worth looking at