Stopping producer consumer loop at the same time

In my application I am using producer consumer architecture. In the producer loop, I am acquiring data, processing and outputting the result (feedback control system). Also in the same producer loop I am inputting all the data to a queue and then in the consumer loop I am writing data to a file. I have a stop control on the front panel and error from the queue and error from the data acquisition all wired to OR gate to stop the while loop. ( I attached the picture of the code). Whenever I press stop form the front panel program wont completely stop. I think it is because consumer loop still running. Is there way to stop the both loops at the same time. I tried creating local variable but it slows the program. Front panel stop control mechanical action is set to switch when released.
Attachments:
app.PNG ‏262 KB

In the consumer loop you should check the error after the Read Queue function.
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What is the best way to stop parallel loops at the same time, from any loop?

If there is a vi with two or more parallel while loops, what would be a good method to simultaneously stop parallel loop execution, from any of the parallel loops? My intent was to try and do this without local variables, so I used notifiers. This seems like an ok method for two loops, but how about for n loops?
In addition, my code has a flaw. I use an OR block to compare the stop status of each of the loops. This works fine most of the time, but if both loops are triggered to stop at the same time,the boolean result will be false, causing the loops to never stop. How can this be avoided?
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Attachments:
parallel_loop_w-stop.vi ‏54 KB

I think you have the right idea, notifiers are one of the better ways to stop parallel loops. You can simplify things by using 1 notifier for everything. I modified your VI to use 1 notifier, it will set the notifier to True ONLY if the loop is stopping, then it stops. The other loop will read the notifier status, and stop based on it the next time it executes.
I also changed the second loop to stop and notify if it has an error (that is usually a good idea, especally if you have I/O or other things that can cause problems)
I also changed the switch mechanical action, that will eliminate the problems for your second question.
The VI's attached are written in Labview 7.0
P.S. If you have 7.1, the Queues are polymorphic, meaning that the typecast operat
ions are NOT needed!
Attachments:
parallel_loop_w-stop7_0.vi ‏45 KB

Time Division Multiplexing and Processing Different Loops at the same time

Hi, I am new in Labview so you may find my questions too silly, sorry about that
I want to design an interface to control the test&measurement devices remotely. I have two desks and there are several devices on these desks. The real problem is to use two different devices at the same time. To do this I heard that I can use time division multiplexing. But I couldn't find enough information about it in Labview. Another advice I heard was to use a matrice and hold the on/off state of the devices in this matrice.
Where should I start the design to create such a system? Do you have any advices? Thank you in advance.
My basic GUI is attached.
Attachments:
InterfaceAli.zip ‏42 KB

As Mike pointed out you cannot communicate in parallel on the GPIB bus - unless you have separate buses for each instrument - and that defeats the purpose of a bus. I am not sure about LXI.
With regard to your VI:
1. Do not use global variables to pass your data around.
2. You should use the Array data type, not the Matrix data type. The Matrix data type in LabVIEW should only be used for matrix mathematical operations (linear algebra) which cannot be easily performed on the array data type. You have many more tools in LV to work with arrays.
3. The Event structure needs to be in a parallel loop. This is basic data flow. If you do not understand this concept, get some training, either though the online tutorials or through a class.
4. Use Value Changed events and place the button terminals inside the event case for that control.
5. The parallel loops need to have a Wait or some other function which causes a delay. Otherwise, the first one to start executing could consume all available processor resources. These are called "greedy loops."
6. Use integer data types for case structure selector inputs. Floating point values are coerced to integers at the inputs. If the values resulted from calculations, unexpected rounding effects may occur, resulting in the wrong case being selected. In some cases using type defed enums may be even better. The underlying data is integer and the enum item names show up in the case selector labels, helping to document what the case does or why it was selected.
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Before going any further with the program questions, you need to carefully define your requirements. How many instruments will you have? How many can be active at one time? What kinds of communication between the program and the instruments is required? This includes commands to the instrument, data returned from the instrument, error handling, and timing requirements. What will be done with the data? Display, save to file, use to automatically control another device? What safety requirements or constraints need to be met? Once you have a good requirements document, then you can begin to determine what kind of program architecture is best suited to meet the needs.
I suspect that you may be making some things much more complicated than they need to be while ignoring other important issues.
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Can 2 while loops work at the same time?

I have two while loops in my program; one reads data and the other does nothing until I hit stop on the first one. I want the first one to always run and the second to run off of the time constraint I have for it when I hit the start button. I am using a DAQ and transfering data from one while loop to the other. See attached file.
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How to attach the start button?
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Go to Solution.
Attachments:
2whlloopprgrm.vi ‏299 KB

Your problem is that the loops have a data dependency. If you want to run both loops at the same time, they can't have any wires running from one to the other. Look into the Producer/Consumer architecture. It uses queues to send data from one loop to the other.
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Timed Loop in Producer/Consumer Loop

Hello!
I have a producer/consumer loop LabVIEW program setup to allow me to properly capture images that are quite large (8MP) at approximately 14 frames per second (FPS). The program works great when the consumer loop is a 'while loop' (records at 14fps no problem), but I wanted to make it into a timed loop, so that I may vary the FPS as required. An oddity arises when I do this. Anywhere below 12fps, the loop works fine and the data is recorded properly. However, when I bump it up to 13fps, the consumer calculated FPS goes haywire and starts jumping between ~9 and ~13fps (data processing gets bogged?). When I set the required FPS to 14, the loop executes at a steady 7FPS maximum. Is there something I can do to rectify this situation?
I have attached my .VI
Thanks in advance!
Solved!
Go to Solution.
Attachments:
ProcessSplitJPG-FPS.vi ‏100 KB

Palanski,
Are you using LabVIEW Real-Time? Timed loops in a windows OS don't really increase determinism more than a while loop with a wait until next multiple timer. Before you changed the producer consumer loop to include a while loop was the programming running correctly? You may also want to vuse the VI analyizer to see how long things are taking to run. I would leave the producer consumer loop in the traditional set up and change the FPS by controlling the wait timer, after benchmarking your code this should be done the same way as you have it for the timed loop
Sam S
Applications Engineer
National Instruments

Run two vi at the same time

I WANT TO HAVE A VI RUNNING (WHILE LOOP, COLLECTING DA DATA, OPERATING AN ACTIVE TEST, ETC.) AND WHILE THAT IS GOING ON, OPEN ANOTHER VI (FROM WITHIN THE MAIN PROGRAM) TO DO SOME SEPERATE FUNCTION (PRINT OUT A LOG REPORT, PREVIOUS TEST RESULTS, ETC.). BUT EVERY TIME I OPEN ANOTHER VI's WINDOW, THE MAIN PROGRAM WINDOW's WHILE LOOP STOPS LOOPING.
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Stopping producer consumer loop at the same time

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