Producer/Consumer Design Pattern with Classes

I'm starting a new project which involves acquiring data from various pieces of equipment using a GPIB port. I thought this would be a good time to start using Classes. I created a GPIB class which contains member data of: Address, Open State, Error; with member vis such as Set Address, Get Address, Open, Close...general actions that all GPIB devices need to do. I then created a child class for a specific instrument (Agilent N1912 Power Meter for this example) which inherits from the GPIB class but also adds member data such as Channel A power and Channel B power and the associated Member Functions to obtain the data from the hardware. This went fine and I created a Test vi for verfication utilizing a typical Event Structure architecture.
However, in other applications (without classes) I typically use the Producer/Consumer Design Pattern with Event Structure so that the main loop is not delayed by any hardware interaction. My queue data is a cluster of an "action" enum and a variant to pass data. Is it OK to use this pattern with classes? I created a vi and it works fine and attached is a png (of 1 case) of it.
Are there any problems doing it this way?
Jason

JTerosky wrote:
I'm starting a new project which involves acquiring data from various pieces of equipment using a GPIB port. I thought this would be a good time to start using Classes. I created a GPIB class which contains member data of: Address, Open State, Error; with member vis such as Set Address, Get Address, Open, Close...general actions that all GPIB devices need to do. I then created a child class for a specific instrument (Agilent N1912 Power Meter for this example) which inherits from the GPIB class but also adds member data such as Channel A power and Channel B power and the associated Member Functions to obtain the data from the hardware. This went fine and I created a Test vi for verfication utilizing a typical Event Structure architecture.
However, in other applications (without classes) I typically use the Producer/Consumer Design Pattern with Event Structure so that the main loop is not delayed by any hardware interaction. My queue data is a cluster of an "action" enum and a variant to pass data. Is it OK to use this pattern with classes? I created a vi and it works fine and attached is a png (of 1 case) of it.
Are there any problems doing it this way?
Including the error cluster as part of the private data is something I have never seen done and ... well I'll have to think about that one.
Ben
Ben Rayner
I am currently active on.. MainStream Preppers
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Similar Messages

Could Buffer replace the Queue in Producer/Consumer Design Pattern

Hello,
I have a question that the task of Buffer is to store the data and the queue is also of the same so could we use the Buffer inplace of queue in a Producer/Consumer Design Pattern.
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No, those buffer examples are not nearly equal to a queue and will never ever "replace" queues in producer/consumer.
The most important advantage of queues for producer/consumer (which none of the other buffer mechanics share) is that it works eventbased to notify the reader that data is available. So if you would simply replace the queue by overly elaborate buffer mechanics as you attached to your last post, you will lose a great deal of the the purpose using producer/consumer.
So, to compare both mechanics:
- Queue works eventbased, whereas the buffer example does not.
- Queue has to allocate memory during runtime if more elements are written to the queue than dequeued. This is also true for the buffer (it has to be resized).
- Since the buffer is effectively simply an array with overhead, memory management is getting slow and messy with increasing memory fragmentation. Queues perform way better here (but have their limits there too).
- The overhead for the buffer (array handling) has to be implemented manually. Queue functions encapsulate all necessary functionality you will ever need. So queues do have a simple API, whereas the buffer has not.
- Since the buffer is simply an array, you will have a hard time sharing the content in two parallel running loops. You will need to either implement additional overhead using data value references to manage the buffer or waste lots of memory by using mechanics like variables. In addition to wasting memory, you will presumably run into race conditions so do not even think about this.
So this leads to four '+' for the queue and only one point where "buffer" equals the queue.
i hope, this clears things up a bit.
Norbert
CEO: What exactly is stopping us from doing this?
Expert: Geometry
Marketing Manager: Just ignore it.

Producer/Consumer Design Pattern + DAQmx + Event Structure

Dear community users,
at the moment I try to implement the Producer/Consumer Design Pattern into my current project. For this purpose I am trying to make a "minimal-example" in which I use the Producer/Consumer Design Pattern for the data acquisition and analysis (display in GraphXY, calculation etc..) process. In the Producer Loop I perform the data readings via DAQmxRead.VI and in the Consumer Loop, in this example only, I display the data in a GraphXY. At the same time I want to control the data acquisition via an Event Structure, for example Start Measurement/Stop Measurement Buttons. To configure the measurement time, for example if the user only wants to measure 150 sec, I use the Time Out Event of the Event Structure. This is a technique which is often used, when data acquisition and Event Structures are used at the same time (Excuse me if this is wrong!). Due to understand the Producer/Consumer Design Pattern I looked up in the Template\Framework of LabVIEW.
In the attachment you will find my "minimal-example", which -sadly-, not working. What should I do ?
Thank you.
Best regards,
tugrul öztürk
Attachments:
daqEngine_PCP.vi ‏35 KB

Your VI will never stop due to the Ok Button that stops the producer loop is read OUTSIDE of the loop. Add an event case for it.
Move the Start and the Ok Button inside of their respective event cases. This will allow the latch to reset when they are read.
Change the Ok Button to a stop button.
Use a Greater Or Equal instead of Equal for the measurement time comparison. What if somebody randomly changes it to 0 on you? Again, you will never stop.
Is the DAQ only supposed to read for "Measurement Time". Right now, it constantly reads. So if you don't use the DAQmx Read, you will get a buffer overflow error. You need to put the DAQmx Start Task inside of the Start event case and then the Stop DAQmx Task inside of the Timeout event case when the measurement time is exceeded. You should also perform the read regardless inside of the Timeout event case.
I HATE telling the consumer loop to stop by destroying the queue. You can look data that way. Instead, send something an empty array. In the consumer, check for an empty array. If it is empty, stop. Destroy the queue only AFTER BOTH LOOPS HAVE COMPLETED.
You should also report your errors in some way. Simple Error Handler at the minimum.
Since you are using Continous Samples, don't limit the buffer. Leave the Samples per Channel unwired on the DAQmx Timing VI.
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Producer consumer design pattern

Hello,
I am trying to build a simple program that does the following:
1. when program starts, the indicator is initialized to -999
2. when Measure button is clicked, the indicator shows random number continuously.
3. when Save button is clicked, the indicator shows 1
I use the event-based producer-consumer design pattern and it works great. However, I cannot find a way to allow the CONTINUOUSLY generating of random number when Measure is clicked. Can someone shed a light on it? Thanks a lot for the help.
Attachments:
CommandList.ctl ‏6 KB
Untitled 1.vi ‏25 KB

One simple way to do it is to use the Timeout event case. You can modify the timeout value based on what events have occurred. See attached mod.
Not saying this is the best way. Kind of depends on where the program goes from here.
Attachments:
Untitled 1-2 MOD.vi ‏27 KB

State Machine and producer consumer design patterns

Hi!
In my application I am using state machine(for top level VI) and producer consumer(for subVIs) design patterns throught out.
If there is no activity on the front panel for 1min then the ideal state is invoked. Following are the situation of the ideal state:
1. It checks for any hardware present on the network . If no hardware is found on the network within 1 min then the application and LabVIEW exits.
2. While the ideal state checks for the hardware, and user clicks on any front panel button then it should exit the ideal state. The control
should be in the respective button state.
I am able to achive the point#1 mentioned above but could not get the point #2 to work. I am including the snap shot of
the state machine(default case) and prouducer consumer(deafualt state).
Each screen has the concept of the ideal state. The only additional step in the subVIs is that when the ideal state is reached and the time has expired then it will close the subVIfront panel.It will go to the exit state of the Main(top level) VI. Thus closing the application and quitting LabVIEW.
Any ideas or suggestions. Will multithreading and notifiers help?
TIA
Rachana
Attachments:
Sanpshot_Of_Design.zip ‏75 KB

Hi Rachana,
I was thinking about using event structures wherein there would an event case that would handle any value change event for any of the buttons on the front panel. But before suggesting that, I would need to know more about the Ideal State subvi( more specifically, how is it checking for any hardware present on the network and where is the one minute wait coming from?).
Please feel free to respond to this post with your questions/comments.
Regards,
Ankita A.

Register event in producer consumer design pattern

Hello wire workers,
I am fairly green when it comes to dynamic event registration, so my understanding of it is probably quite flawed, but what I have implemented seems to work fine.
Assuming a fairly typical queued producer/consumer state machine architecture.
Up till now, I have done the dynamic event registration outside (i.e. to the left of) the UI loop, so all events get registered before the UI loop starts to run.
My question is:
How can I register events from inside one of the consumer loops? I cannot wire it...
Maybe an example will make my scenario more clear.
I have a DAQ loop (queued state machine). In the init state of this loop I want to register a digital input such that changes on a line are handled by my main event structure (in the totally separate UI loop). Is this possible?
I look forward to hearing positive answers
nrp
CLA

The best way to send data from the Consumer Loop to the Producer Loop is through User Events. What you will want to do is create a User Event whose data type is the registered DAQmx event refnum. Then when you register the DAQmx event in the Consumer Loop, fire the User Event with that new refnum and update the registration in the Producer Loop. That's probably hard to wrap your head around in words, so I'll attach a dummy example and pic below. Hope this helps!
VI Saved in LV85.
Message Edited by Jarrod S. on 04-21-2008 12:54 PM
Jarrod S.
National Instruments
Attachments:
DAQmx Event.vi ‏30 KB
DAQmx Event Pic.PNG ‏38 KB

Producer/ Consumer Design error?

I am learning labview as I go and little errors keep stumping me. I set up the producer/consumer design and it reads the two while loops like I want. However, when I stop the program to save it to the write to measure it gives me an error saying invalid input and highlights the dequeue. I have to queues running (one for a button and one for data) and they both do this. I tried connecting it different ways but its always the same error. Any ideas?
Attachments:
2whlloopprgrm.vi ‏392 KB

Dublicate post
Stick to one post at a time. Do not post the same question on two different threads.

Producer Consumer & User Events with user input windows

Hello All,
I am planning to build Labview code using the Producer Consumer & User events pattern, the application needs multiple user input windows for things like personal data, feature selection etc, there could be around 15 or 20 distincts screen/panels required.
The main question from me is... Is there a best practive approach to navigating/loading from one window to another etc, and also providing a way to to retrun to the previous window.
Also I may need need to be running some slow logging and control hardware in the background while navigating some of the screens, this seems like the producer consumer vi will be running in the background while the user input causes a load/display window event.
A simple Producer Consumer multiple winjdoow example would be very welcome. Thanks.
Regards Chris

I will second Mike's suggestion to use a central VI with subpanel(s). It is usually less confusing than multiple windows. Typically, the selection/navigation mechanism is on the left of the main panel, global info (like help) on the right, and the subpanel(s) in the center.
The advantage of subpanels/subVIs is that you can launch your subVIs and keep them active in the background, even though they are not being used. This means they will keep their state information and load into the subpanel almost instantaneously the next time you need them. For a short tutorial on subpanels, check out this link. Scroll down to the fourth reply for working code. The original code posted is broken.
Communication between your VIs or loops is typically done with either queues or event structures. State information in each should be shift registers in the respective VIs. If you have the time, I would highly recommend you learn how to use LabVIEW classes. The command pattern is tailor made for this kind of application.
Finally, avoid global data if you can. Global data is anything that you can get to from anywhere (globals, functional globals, etc.). Use of these can speed your development, but can also lead to sloppy design which will cause you major problems later. If you really need globally available data, use a data value reference. It is unnamed and requires a reference, which tends to enforce better programming practice. Yes, there are instances where you truly need globally available, named data, but they are fairly rare. You should only use them if you are experienced and really know what you are doing.
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ETL design pattern with Data Integrator

Hi all
I have searched a lot on the SAP website and also on the Google to find a reliable document about ETL design pattern which applies to BO Data Integrator, but it was not successful. Most of the links I found was for SSIS and Informatica,....
I would be grateful if you could guide me to a good link about ETL design pattern.
Thanks.

I would start with these two:
https://wiki.sdn.sap.com:443/wiki/display/BOBJ/ETLProjectGuidelines
https://wiki.sdn.sap.com:443/wiki/pages/viewpage.action?pageId=49414406

Factory Design Pattern with Java generics

I was wondering if it was possible to implement the factory pattern using a generic like sintax with java5. Something like:
IFactory factory = new ConcreteFactory();
Car c=factory.CreateObject<Car>();
I saw this article the other day http://weblogs.asp.net/pgielens/archive/2004/07/01/171183.aspx
done in C# for the framework 2.0 and tryed to re-implement it with java5 however I was less then fortunate, can someone do a functional conversion?

I had to change the signature a bit but this is the best I came with:
(I don't like I have to write Type.class but if someone has a better idea please share, I deliberatly used classes are return types but you can easily program to the interfaces as well)
use:
ConcreteFactory cf=new ConcreteFactory();
Car c=cf.Create(Car.class);
public interface Vehicle {
String getName();
public class Plane implements Vehicle {
String name="Mig 29";
public String getName() {
return name;
public class Car implements Vehicle {
String name="Volvo";
public String getName() {
return name;
public interface IFactory{
<T> T Create(Class<T> type);
public class ConcreteFactory implements IFactory {
public <T extends Vehicle> T Create(Class<T> type) {
try {
return type.newInstance();
} catch (InstantiationException e) {
return null;
} catch (IllegalAccessException e) {
return null;
}

Localization design patterns with TopLink

Hello,
We are creating web app with JSF and TopLink.
Each table in database may have several fields that can be localized.
All localization resources are stored in a table that has such columns: table_name, column_name, language, localized_text.
How would you suggesting implement localization using TopLink?

Sorry, I missed one column.
Columns in localization table: table_name, column_name, row_id, language, localized_text.

First attempt at Producer Consumer Architecture: continuous read and dynamically update parameters.

Hello,
I am currently working with two instruments; an Agilent E3646A and an NI 6212 BNC. My objective is to have the 6212 to be continuously taking measurements according to predefined parameters while the E3646A's parameters can be continuously updated. This simple instrument combination is intended to help me learn the necessarry achitecture; continuous measurement, dynamic output control, and more instruments will be added in the future.
I've previously posted on a similar, but more complicated, setup (http://forums.ni.com/t5/Instrument-Control-GPIB-Serial/Split-second-lag-when-controlling-two-instrum... and was advised to try the Producer Consumer Architecture. I've found relevant literature on the site (http://www.ni.com/white-paper/3023/en/, https://decibel.ni.com/content/docs/DOC-2431), searched the forums and constructed my own VI. While my first attempt at a Producer Consumer Architecture has resolved some of the issues I was having when I first posted on the subject, however, new issues have arisen with regard to reading and stopping the VI.
I am currently able to run the VI and update the device parameters. Previously, I would get a freeze while the instrument was being updated and could not toggle parameters until it was done. This has been resolved although the read only updates when a parameter has been updated although it is outside of the event structure. Furthermore the Stop button does not work in any context. I've also gotten occasional errors regarding the Deqeue Element but the bulk of the trouble is Error -200279 "Attempted to read samples that are no longer available" at DAQmx Read. I realize that there is a problem in my Producer Loop but haven't been able to figure out how to resolve it.
This is my first attempt at a Producer Consumer Architecture and already I can see that it is a powerful tool. I read as much as I could and looked at the relevant examples but expected to have some issues in the beginning. Would really appreciate any advice so I can take full advantage of the architecture.
Hope to hear from you,
Yusif Nurizade
Solved!
Go to Solution.
Attachments:
DCe3646A_DAQ6212_Prod_Con_4_13a_2014.vi ‏89 KB

Jon,
Thank you for the response and the suggestions.
I created the Local Variable for the Stop Button and moved the original into its own Event Case. It is now able to stop VI execution although I get Warning -1073676294 which I understand to be the buffer issue. The warning says that this was incurred on VISA Open for the E3646A's Initialize VI which is outside both loops, however, which I don't understand.
I tried increasing buffer size by decreasing the Number of Samples as per suggestions I found on NI forum threads. I've brought it down as low as 1 but the graph still only updates when an Event occurs and I keep getting the same buffer error. You suggested that the problem could be that they are in the same loop; does this mean that the DAQmx read should be outside both Producer and Consumer Loops or moved into the Consumer Loop? I found a couple of links ( http://forums.ni.com/t5/LabVIEW/Producer-Consumer-Design-Pattern-DAQmx-Event-Structure/td-p/2744450 , http://forums.ni.com/t5/LabVIEW/Producer-Consumer-Architecture/td-p/494883 -first response) on dealing with an Event Structure that my own VI is based. Alternatively, I found another link ( http://forums.ni.com/t5/LabVIEW/Producer-Consumer-Design-Pattern-DAQmx-Event-Structure/td-p/2744450 - first response) on a DAQmx Read with an Event Structure that places the graph in the Consumer Loop.
The core of my purpose in setting up this Producer Consumer Architecture is so that I could read continuously while the instrument parameters are updated dynamically so it's very important that I understand how this works. I am particularly struggling with how the Event Structure is controlling the While Loop's Execution.
Hope to hear form you,
Yusif Nurizade
Attachments:
DCe3646A_DAQ6212_Prod_Con_4_14a_2014_Edit_I.vi ‏90 KB

Is this a good design pattern?

Hi,
I am working with a team to create an application that can acquire data from up to 24 thermcouple channels. We plan to create a wizard to assist the user in setting up the test (specifiying stop conditions, sample rate, channels to sample, output file, and email/text notifications). After the setup, if the user does not cancel out, then the program continues. We have defined parallel loops and their roles, trying to fit into a producer/consumer design pattern. I have attached the main file which shows the structure of the program. We are trying to keep it clean and modular. Before diving into development, we are finalizing a detailed design specification so that different people can work on each of the loops' subvis. I was hoping that people could review the block diagram and offer suggestions for improvement or validate that we have chosen a good method of implementation.
Notes about the block diagram
The plan is for data driven stop conditions to be detected by Event Notifier, handled by the Main UI event, and then the Data Collector is instructed to stop (as well as the Main UI loop). When Data Collector stops, it releases queues, the queue reference becomes invalid, and then the loops with the Dequeue will be stopped.
I am not sure if an additonal event structure should be in the DataCollector to specifically handle the Stop button on the UI because if it is in the Main UI event structure, the DataCollector would not be stopped immediately. This is important to stop quickly because the sample rate could be VERY long. I understand about using an event structure instead of WAIT, but didn't know if there is an efficient way leaving it down in the Main UI event structure....????
Data Collector is the producer, it currently only collects data and passes it on. If the program is going to contain a start collection button, or pause/resume, I need to figure out how to handle this with the Main UI event structure.
Event Notifier consumes data from the Data Collector. It looks at all data and should set a flag if a stop condition is met. The flag will be handled by the Main UI event structure to tell Data Collector to stop. The event notifier also sends a notification to the Email/Text Caller when thresholds have been exceeded warranting a reason for the user to be notified via text or email.
Email/Text Caller waits for notification and then calls a subVI to send an email or text with certain data and channel information. The subVI call is lengthy, so we decided to put this in its own loop instead of a case structure inside the Event Notifier.
Report Generator logs all collected data to a file. A second queue was used, but uses the same data as the first. Is this the correct implementation since two consumers need the same data?
Main UI - handles changing of sample rate, possibly the stop button, possibly start/pause/resume of data collection. Also handles when Event Notifier sets flag for a data driven stop condition, which then should provide a mechanism to stop the Data Collector.
A big question that i have is.... Should the Main UI event structure just be in the Data Collector so that the loop can be stopped immediately? All of the UI events (stop button, start/pause/resume data collection) directly effect the Data Collector. Should the data Collector have a state machine instead?
I feel that the 3 consumer loops (Event notifier, Email/Text Caller, and Report Generator) seem like a good implementation, but i am not confident about the Data Collector and Main UI loops. Should they be combined?
Solved!
Go to Solution.
Attachments:
updatedMain.vi ‏13 KB

A couple of thoughts:
Overall it looks workable- remember to name your queus and notifiers- then you can depop the BD and launch each loop in its own sub-vi without wiring all those queues between loops- Just obtain ref to named queue.
"Data collector" needs a supervisor to control how often the data is collected- I'm thinking a QSM with "init- collect- stop" states. A simple timed loop could produce the "time to acq ticks" under control of the sample rate control. This puts both the DAQ init and cleanup functions within the Data Collector's perview so it aids coehesion and solves the exit without waiting for the loop to iterate.
I'm not a fan of duplicating data- I assume analisys is pretty much just some comparisons- so it is pretty quick- Why not append summary data to the same queue? And make it a single element queue- the report loop can then inspect the queue and look for a summary data "index" - if its greater than the last index written append the darn data to the report? Preview queue works great for these situations.
Do not combine the UI handeler with anything else! Do you see the snag?- hint: here thar be spaghetti. keep the functions seperated for solid scalable and maintainable code.
One last thought: Its getting less popular to stop loops on the error out of a dequeue. First it returns a default element that can cause your listeners some headaches. Second it doesn't let you run cleanup code. Use a stop command <enum> built into the element data as an executive to determine when to stop. We'll try to get the examples updated to show current best practices.
Jeff

Producer consumer "clean up diagram" puts consumer on top of producer

I do File > New... > VI > From Template > Frameworks > Design Patterns > Producer/Consumer Design Pattern (Events)
Then without doing anything to the block diagram or front panel, I click on the "clean up diagram" which does the auto block diagram cleanup. Bam! Consumer loop is put on top of Producer.
I tried a bunch of combinations of the Block Diagram options settings (wire spacing, move controls left, etc.) , but the "clean up diagram" always wants to put consumer loop on top of the producer loop. How can I get labview to maintain the original loop positions?

There is a reason a lot of use do not like to use the Block Diagram Cleanup. It generally works for simple VIs. But I would not use it on my top level architecture.
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Recommend design pattern books

Hi
I work at a university and I am looking for some books on design patterns in LabVIEW, preferably for 2009.
I am interested in state machine and master/slave design and perhaps also producer/consumer design pattern.
Can you recommend some books on these techniques.
Simon
LabVIEW 8.6 / 2009 / 2010
Vision Development Module 8.6 / 2009 / 2010
VBAI 3.6 / 2010

The LabVIEW Style Book by Peter Blume has a chapter devoted to discussing patterns in LV. If you want to go generic and not pin yourself to one language, the classic of the subject is Design Patterns by Gamma, Helm, Johnson & Vlissides - that book has been on my shelf ever since I used it as a textbook over a decade ago.
Greg
Certifed LabVIEW Developer

Producer/Consumer Design Pattern with Classes

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