Producer consumer loop

I have a Producer consumer loop that is reading in data from a Excel File call sample1. There is a third party software that constantly writes data to the same excel file Sample1 every _ amount of seconds. Every time the Third party software writes it will over write the excel file data. So it may only be 5 columns and 3 rows.
1. I need to make sure that there is not a conflict when the Third party software has the file locked to read and Labview is trying to read.
2. I need to make sure that if labview isn't reading and reading before the Third party software writes so basically i need some way of checking labview isnt reading the same data twice i need to make sure the file has been updated before it tries to read again. The problem comes in when you can't regulate the time that the third party software reads.
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Attachments:
VI snippet (2).png ‏123 KB

I've had to write code for similiar applications. It is tricky.
Have a look at the .NET FileSystemWatcher.Changed Event. This might be a good way to monitor what is happening with the file.
Take a look at this post: http://forums.ni.com/t5/LabVIEW/My-First-Nugget-Directory-Changed-Event/m-p/1407552/highlight/true#M...
"There is a God shaped vacuum in the heart of every man which cannot be filled by any created thing, but only by God, the Creator, made known through Jesus." - Blaise Pascal

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Can anyone tell me what's wrong with my queue or producer consumer loop?

A Labview engineer helped me with the overall structure of my program, necessitated by the fast data sample rate and post processing requirements. He recommended the producer/consumer loop and using one of the example files (Cont Acq graph voltage - int clk) to do the actual data acquistion. So I put together the loop and go my two channels of data acq going in the producer loop. However, nothing's getting picked up in the consumer loop and none of my data gets displayed over there.
Anyone care to take a look at it and let me know what I'm doing wrong?
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Attachments:
P-C Yanmar Program.vi ‏296 KB

Your Enque Element should be inside the while loop where you aquire the data. As it is now, the data has to stop being aquired before you send the last set of aquired data.
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Producer consumer loop for serial comms

I have an application where I am trying to read and write to a serial port using a producer consumer loop. My producer consumer loop seems to work fine until I put the serial comm VIs in the consumer loop. Prior to that my event structure in the producer loop seems to work fine and all the controls on the front panel send commands into the queue and the expected reaction happens in the consumer loop. When I put serial comm VIs into the consumer loop the application will read the serial port but none of the other controls on the front panel ever get any reaction from the consumer loop. I am not sure if I am using the producer consumer loops correctly when using comms at the same time. Any help would be appreciated!!
I have attached the VI for your inspection.
Attachments:
pinger comms.vi ‏65 KB

You could probably continue with your original architecture as well. Just put the check for bytes at port in the Read case of the consumer loop. As you said, it takes 1-2 seconds for the device to send data. So the original architecture didn't work because you were queueing up 20 reads per second in the timeout case, but the consumer loop was taking up to a second for a single byte to come in.
If you check for bytes in the consumer loop, if none are there, the Read case will end quickly and won't wait for that byte to come in.
You should also probably increase the timeout of the event structure to 100-200 mseconds or even more. The event structure would still respond instantaneously to user interface events. And you would only be generating the timeout case a few times per second. Which means when a byte comes in, it would probably be sitting there only 100 mseconds or so before you read it. Unless you go click happy and generate lots of other events not allowing the timeout case to run.

Data delay in producer consumer loop?

Hi,
I've been creating an VI using producer consumer loop. In producer loop, every loop take 1000 samples at the rate of 40000/s(or 40000s/s devided by number of channels) and the consumer loop will average the data in a way corresponding to the "sampling rate" value on the front panel. The "sampling rate"represents the data rate on the chart and in the saved data file. If it's too slow,say 1 sample per second, then the producer loop will just wait for some time.
So far the VI run smoothly, but there's one big problem. Each time I adjust the amplitude of input signal and the change doesn't show up on the chart untill several seconds later. When the "sampling rate" is really slow, the delay could be 1 minute! It's the first time I have ever used producer consumer loop and I 'm really confused of what causes this time delay.
Could someone give me a hand with this?
Thanks!
Yaqiong
Attachments:
parallel.vi ‏73 KB

You should consider further separating your tasks. For instance, the writing to file should be in its own task since file I/O can really cause delays in your processing. Also, I would separate your data processing (averaging) from the UI updates. The UI updates can be within a task that is using an event structure. It can get the data updates to update the chart but it can also quickly respond to the changes in your amplitude. I would also be very careful of the wait in your producer loop. This could starve the CPU.
One last note. Your code could really benefit from a cleanup. Your coding style is quite a mess and it makes reading (and maintaining) your code much harder. For example, your code should generally read from left to right. Running wires backwards, having outputs on the left, lots of bends, etc all lead to messy code that is difficult to read.
Mark Yedinak
"Does anyone know where the love of God goes when the waves turn the minutes to hours?"
Wreck of the Edmund Fitzgerald - Gordon Lightfoot

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!
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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

Basic Producer/Consumer loops for a newbie

Labview neewbie here.
I was looking at Producer Consumer loops.
Can anybody give me a very basic explanation of how to set one up.
I want to take readings from a HP 53131A counter and store them in an excel spreadsheet.
I understand the part about labview slowing down as it opens the Excel file, and a seperate loop will help solve this.
But I dont understad how to set up the Que function.
Thanks.

Multithreading will not make excell open faster but using concurrency you can have more than one operation operate ate different speeds. The nice thing about the produce consumer model is that the if the consumer is slow or unreliable (freeses up) the producer doesnt care and will continue. To use a queue is very simple, 1. create the queue, name it(optional) and give it a data type (ie int, array of floats ...) in the produce loop use the enqueue vi to add items as needed to the queue, in the consumer dequeue these items (using a timeout = -1 the loop will wait for a new item and not consume resources) the consumer can process the data acquired in the producer loop.
Paul Falkenstein
Coleman Technologies Inc.
CLA, CPI, AIA-Vision
Labview 4.0- 2013, RT, Vision, FPGA

Synchronizing 2 graphs / producer-consumer loop stuck

I have a pretty huge VI here, so I created a smaller one, which shows my problem.
First thing is, the user has to set some parameters, before the VI is running. So, I created a sequence with a while loop. If the user hits the button, the loop ends. That works pretty well.
In my huge VI I am doing data acquisition. The user hits the button in order to acquire data, checks the data and the data is saved when he hits the acquire button the next time.
Next thing is, I have two graphs. When the user zooms one graph the scale of the other should be updated automaticaly. Therefor I created a loop with a event structure in it. If the user hits the button in order to acquire the next set of date, the loop ends. So far so good, this works pretty good as well.
But now - if I zoom the graph before I hit the button in order to end the while loop, everything gets stuck. I don't know how to get rid of that behaviour.
Please do not suggest anything like getting rid of the producer/consumer loop, since I specifficaly need everything that is in the VI for a certain purpose.
If you need any additional information, please just ask. I hope my problem is described well enough so far.
Attachments:
zoomprob.vi ‏41 KB

thanks for the response,
the upper event structure will trigger the data acquisition process, so I don't want to have any time out value unless the user wants to start the acquisition process.
the lower event structure will take care of the state when the acquisition is done, but the user wants to examine the aquired data. Using a longer time out will not be a disadvantage, but I think it will not solve the problem alone.
At the moment everything works fine, if you use it how it is ment to be used. If you aquire data and then mess up with the graphs scale, everything is good. But if you try to manipulate the graph and then acquire data, it gets stuck. Apperently, that is not how it's ment to be used - but you know what users often do...
Unfortunately the highlight execution is of no particular use. If I turn it on and manipulate the graphs scale, the vi gets stuck, but no specific process is shown in the code. Apperently it is waiting for a event, but it isn't triggered. So, beeing able to disable an event structure and enabling it later would solve the problem, for example.... I haven't found any solution for dealing with that, unfortunately...

Producer consumer loop array building

Hello,
I am trying to build an array in the consumer loop of a queued vi. This is the first time I have tried to use a producer-consumer structure since class many months ago. Each element is queued and sent to the consumer loop, and in that loop I want to build an array of the elements before I save it to disk. For some unknown reason I am having trouble accomplishing this. Usually I throw this stuff into a for loop, but here it isn't working.
I am converting the random number to a string in the producer loop because when I build the real program I will be using strings.
What am I missing?
Tay
Attachments:
Loop test.vi ‏35 KB

Just built your array in a shift register.
(The error case is simply wired across.)
Message Edited by altenbach on 05-16-2008 08:03 PM
LabVIEW Champion . Do more with less code and in less time .
Attachments:
looptest.png ‏8 KB

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.
TOn
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Producer consumer loop only execute once?

Hello here,
In my VI, the producer loop seems working continuously, but the consumer loop only execute once.
I haven't used producer/consumer pattern before, could someone give me some ideas why this happens?
My code is in attachment.
Thank you in advance.
Yaqiong
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Attachments:
parallel - Copy.vi ‏72 KB

That would be the poor choice of using an event structure in the consumer loop. As set up you must generate a mouse Leave or mouse enter event on Waveform Graph for the consumer loop to finish its first iteration.
Delete the event structure. you don't need it to update a graph.
Jeff

Consumer loop slowing down producer loop

Hi All,
I'm currently using a PXI to send commands to a chip, then retrieve the results with a DAQ. This process loops to populate a 256x50 array of values.
Each time the loop is fully populated, I want to display the result onto a 3D plot, using 3d plot lvclass and plot helper. I noticed through the profiler and using timing functions in the loop that the 3D plot would take ~200 ms to update. The array would fully populate in about 100ms, so tripling the time to update was kind of nasty.
I put the 3d plot into a consumer loop and everything else in a producer loop. It works fine, I don't mind about dropped frames, but it was running at the same speed. Apparently whenever the consumer loop executed, it would freeze completely the producer loop.
Why is this? It seems like this fellow had the same problem:
http://forums.ni.com/t5/LabVIEW/Producer-Consumer-Loops-not-independent/td-p/1115665
But he "solved" it by removing the graph altogether. As showing the graph updating in real time is critically important, I can't just chuck it.

No, an action engine is sometimes called a LabVIEW 2 Style global. They are basically a VI with a while loop and an unitialized shift register. They are useful when passing large amounts of data since it does not get copied. Also if you have transformations that are made on the data it is a single self contained VI that has data and actions which can be performed on it. Today a LVOOP implementation would be prefered. At any rate, this is a non-reentrant VI which will cause blocking to occur if called from two or more loops at the same time.
Out of curiosity, what type of graphics card do you have in the PC? Would a better graphics card help?
Mark Yedinak
"Does anyone know where the love of God goes when the waves turn the minutes to hours?"
Wreck of the Edmund Fitzgerald - Gordon Lightfoot

Input and output on same device, producer/consumer structure

Hello interested people,
I have a question about using the same device for both digital inputs
and outputs. I have written a simple program of one while loop
that continuously polls the device, processes, and requests. I
have addressed the device using two DAQmx Asst. and I have attached
them with their error in/out cluster terminals to provide data flow and
eliminate the chance of addressing the devices at the same time (which
produces an error). Now I want to change this program structure
to a producer/consumer loop foundation with state machine.
In this design, I will have the DI in the producer loop and the DO in
the consumer loop, under one of the states. I can't simply
connect the error in/out ports in this configuration, so my question is
how to avoid the error caused by addressing the same device
simultaneously with two different tasks (input and output)? I
have attached two VI's, the "One Loop" vi is the original configuration
(simplified), and the Producer-Consumer vi is a NONSENSICAL program
that simply represents the desired configuration. (I don't need
any comments on the programming of this vi, it is only an example for
illustration of the problem).
I am thinking about bundling the input data and the error cluster, both
from the PXI 6528 DI, into one cluster, queueing that up, and
unbundling the de-queued elements for some kind of data flow between
the producer loop and the "Request" state of the consumer loop.
Is this the right approach, or am I barking up the wrong tree?
Thanks
Attachments:
One Loop DO DI.vi ‏102 KB
Producer-Consumer DI-DO.vi ‏106 KB

Hello,
It sounds to me like you really have two modes:
1. user interface actions determine execution
2. user interface is locked, and execution is automated.
I think it would make sense to use the producer consumer for an architecture. Basically you would do the following:
1. program the producer to handle the user interface as you normally would.
2. provide one additional event case in the producer which would be your "automated handling" case. In that case, you could put a state machine which could run until whatever conditions were met to put your program back in "user interface mode".
Keep in mind that you can use custom USER EVENTS to programmatically generate events ie. you can trigger the start of your "automated handling" form anywhere in your code at virtually any time.
I think this would allow you to take advantage of the producer consumer architecture in its intended spirit, while integrating an automated routine.
I hope this helps!
Best Regards,
JLS
Best,
JLS
Sixclear

Producer Consumer simultaneous operations at different frequencies

My goal is to do two operations simultaneously.
The desired end result is:
1)      Produce an output signal which oscillates at a specified frequency (1 to 10 hz)(using DIO NI-9403). This signal will cause a solenoid to vibrate at different frequencies.
2)      Monitor voltage on 3 lines in real-time (using analog input NI-9201). This will monitor system response to vibration.
3)      Produce an output signal which oscillates at a different frequency from (1) – producing 1-second HI values 5 seconds apart. This will cause the system to “pulse”; system response will be monitored.
4)      Have a front-panel user interface where: the signals in (2) can be monitored; frequency of (1) can be monitored and changed; and the output on (3) can be monitored and changed.
My efforts so far have been to build a producer-consumer structure. This is my first time using this structure so I may be completely misunderstanding its use. Feel free to correct me if I’m way off target.
The issue I have is the solenoid in the consumer loop (which handles item (1)) is not operating at the desired frequency. It is too slow. I used a 10ms timer for this loop, but instead it is operating about 1 cycle per second.
There may be a much better way to approach this, or maybe my program only needs some minor tweaks. Either way, thanks in advance for your help.
Attachments:
ProdComsLoop Pulser 2-27-14.vi ‏65 KB

Hi BradleyDDC,
It seems from your program that you don't need a producer consumer loop. The only thing you are feeding from one loop to another can be put in one loop, I mean the simulator on button.
The timer does not determine how fast the loop runs in real time. To get more precise timings, we recommend hardware timed operations as opposed to the software timed ones.
Instead of using a digital output signal, you can use a counter output task, here is a knowledgebase, which has an example of what you may want.
Paolo F.
National Instruments
Applications Engineer

Insert a DAQ assistant in producer consumer vi

Hi,
I am using a DAQ assistant to receive the measurements in the 10 digital ports.
Hence I use the DAQ assistant icon in the vi s to get these data in to labview.
Now I require it to convert these digital values from DAQ assistant into analog( this i have done )..
Thse analog values are to be taken one at a time for further processing.
I am trying to use this produces consumer loop for it..http://decibel.ni.com/content/docs/DOC-2431
however i dont know where to fit in the daq assistant .
Do i still need the DAQ create channel , sample clock etc?
or do i simply place my daq assistant in the place of the create channelDAQ icon?
thanks for any help..
iam completely confused as to what to do with it!!...
Regards,
ruser

Hi,
Thank you for the suggestions..
i am sending one vi here..
this is my basic vi which gets the data from the DAQ and converts it into data ( angular info) we require ie angular position data of lower and upper encoders. This is a continuous real time prcess, which will stop when we press stop in the vi.
Now i want to take the a set of data (input and output) each, send it to a vi which will receive this set of data; process it and repeat this for the second set of data etc..
I am also attaching the lvm file . which is the data we are saving now.
The first attachment is the vi where i am getting the data.
The second attachment is the lvm data file.
Thanks.. I would appreciate any help here...
ruser.
Attachments:
absolute encoder.vi ‏805 KB
LabVIEW Measurement file.docx ‏17 KB

Releasing Queue in Producer Consumer model

I am having a VI which reads data from ethernet,writes to disk,processes and displays. Since lot of processing and displays are there, I am converting it to a Producer- Consumer model so that no data is lost.
I am using 2 loops. IN the Producer I am doing the UDP read and Write to disk functions.and use the enqueing also.In the Consumer loop I am dequeing it and do all the processing and displays.My idea is to avoid any data loss in UDP reception and file writing.
My confusion- where to use the release queue?from the Producer or Consumer ? In a third loop ? Should it be in a sequence structure ?
How to set the loops stop conditions ?
My requirements for stopping - when I press the stop button the program should stop completely(the Consumer loop should stop only after dequeing and processing all the data in the queue). If i don't press the stop button the whole program should run continuously (if data does not arrive for some time it should wait without time out-i am using -1 for the time out condition in UDP read.)

Here is the ultimate Producer-Consumer loop. It queues a stop command when the stop button is pressed. This ensures that every element is dequeued and processed before the bottom loop stops. The last queue data to get processed is the stop command because after you press the stop button, the top loop stops enqueueing more elements.
If your data type is other than a string, you can create something to represent stop, like NaN for a numeric.
Notice the shift registers. This is good practice. Every loop starts with an error out of the previous loop. If an error occurs, it is passed on to the next loop iteration. Also, if an error occurs in the consumer loop, the loop stops. It is good practice to put shift registers on the queue reference also, but not necessary in this case. If you use a For loop, and the loop iterates 0 times, the output of the queue reference would be a null reference, and the Release Queue would not release the queue. With While loops, they always iterate at least once, so it isn't necessary. Its just good practice to make a habit of using shift registers so you don't forget when using For loops.
Notice also that the error in to the Release Queue is not wired. If there were an error, the Release would not take place. All errors are merged at the end to report exactly where an error occured. A timeout is included in case an error prevents the stop command from being enqueued or dequeued.
- tbob
Inventor of the WORM Global
Attachments:
ProducerConsumer.vi ‏53 KB

Producer consumer loop

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