What is ment by 'producer/consumer approach'?

What is ment by 'producer/consumer approach'?How would I implement into the program shown in the screenshot below?
Cheers
Sam
Attachments:
wind5.png ‏91 KB

In your program the DAQ and IO assistances would be the producers, and the filewriting would be the consumer.
Look here for more info.

Similar Messages

What is the Fastest producer consumer method. Queue, RT-FIFO, Event

Hi all,
Another curly question for the pro's:
I have recently inherited some labview code that uses RT-FIFO for the transfer mechanism in the producer consumer architecture.
The code was first written 3-4 years ago and is presently in LV8.6. It is possible that the reasons for the architectural decision no longer exists.
I am skilled using a queued producer consumer architecure,
I understand the RT-FIFO Architecture.
I have begun using a user Event Based architecture.
(I have attached samples of each)
I also see the existance of a priority Queue
Each method has it's own capabilities and deficiencies, That aside, does anyone know the relative performance of each method.
(Assuming single process)
I would expect RT-FIFO to be fastest, it appears to be a low feature version of a standard queue.
What is the perfornace hit for using a more coding freindly Queue
The RT-FIFO description speaks of commications between time critical and lower priority threads.
Until today, I believed that Queues had the same capability.
I have included an event method I commonly use for peer review and to help to fellow users..
It allows:
1. Multiple producers with different data types
2. Processes repecting order of production.
3. Allows for asynchronus checking of functional notifiers such as stop, start and abort.
4. In a non real time system it can include front panel interactions.
What I don't understand about it is what overheads, or thread priority changes that may be experienced by using this architecture (it solves a lot of problems for me).
Thanks in advance,
iTm - Senior Systems Engineer
uses: LABVIEW 2012 SP1 x86 on Windows 7 x64. cFP, cRIO, PXI-RT
Solved!
Go to Solution.

Are you running into a situation where the difference in time between producing an event, and consuming it, is actually causing your problems? If not, this is not a question worth worrying about. Use whatever is most appropriate for your application.
There's no need to make wild guesses - build a VI, benchmark and test! The attached is a reasonable starting point, although I think the event structure may be slow due to setup time but may respond quickly once running. If you experiment with this, you'll probably find that there's no definite answer to which is fastest. Changing the size of the RT-FIFO, or of the queue, makes a big difference in speed. At least in my testing, a single-element RT-FIFO is fastest, but an infinitely large queue is faster than a small queue, and a longer RT-FIFO is much slower than the single-element version.
It's important to realize that RT is not another word for Fast or Efficient, it's another word for Consistent. For the purposes of real-time (deterministic) execution, it doesn't matter how fast the RT-FIFO functions are so long as they execute in exactly the same amount of time, every time (with the exception of a "forever" timeout value, of course). You can use either a standard queue or an RT-FIFO to communicate between loops. One use for an RT-FIFO is when a time-critical loop is enqueuing the data. It guarantees that the amount of time needed to put data into the FIFO will not vary. Enqueueing data in a standard queue will sometimes be faster than other times, depending on whether there is already space available in the queue or space needs to be allocated for the new element. If this variation is unacceptable, then use an RT-FIFO; otherwise, the standard queue works just as well.
If the architecture shown in your image is working for you, I don't see any reason to change it.
EDIT: oops, almost forgot to attach the code I used for testing!
Attachments:
Event vs Queue.vi ‏21 KB

Help? Looking for better approaches to mutlithreading, parallelism (producer/consumer)

Hi,
   So II would like to do some parallel processing of data using the multiple cores of my computer, and I'm trying to find a way to do this in labview. I deally, I would liek to be able to take a given task, put the work into a work queue, have threads from each processor take a task from the work queue and process it in parallel until the work queue is empty, and put the result into a results queue where I could then write the results to a file. So in a text-based languange, the implmentation would be straightforward.. but I'm not sure how to go about this in Labview.
       I've read about the different designs patterns, and was trying to use a Producer/Consumer approach with queues. What I wanted to do was read a list of files from a directory, stuff the paths into a queue (Work Producer), then have a second loop (Work consumer/Results Producer) dequeue each file, process it, and send the results to a second queue. Then at the end, a final loop (Results consumer) would read all of the results.
My question now is.. is there a way to do this more cleanly than what I have on the diagram? Right now, I have to know in advance how many parallel tasks I want to use, then I have to wire up each task before executing the program. If I move to a different computer, I need to change the wiring digram. Is there a way to abstract this to avoid having to make huge changes to the block diagram? I was considering trying to make the parallel portion fit into a subVI so that I could just copy and paste several sub-vi's to easily add and remove parallel threads..    but its not so simple to have to keep track of all the queue references, and etc..
Has anyone already done somoething like this? I feel like what i'm trying now is becomming a big mess
Thanks

You can run clones (instaciate from tempaltes) of the crunching code where each get a ref to the queue based on its name. When they see the queue is empty the terminate and close.
Make sure your queue is full be fore you lauch them.
There is supposed to be new property that tells you how many CPU you have but I can't find it at the moment.
Have fun!
Ben
Ben Rayner
I am currently active on.. MainStream Preppers
Rayner's Ridge is under construction

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?
Solved!
Go to Solution.
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 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

Producer consumer error 200279

Hello,
So I’m about to go crazy and hoping someone can help me here. I’m writing a program that controls a motor and using a producer/consumer method to write the data at 10,000 intervals a second. I’ve read through multiple examples and I don’t see what I’m missing. I’m trying to record 18 different readings from a DAQ 9178, 3 readings for voltage module NI 9205, 1 reading for current module Ni 9203, 2 readings for accelerometer module Ni 9234 and 12 readings for temperature module 9213. Every time I run the program I keep getting the error message 200279 and it states that it’s trying to read samples that no longer exist. It advised me to increase the buffer rate. So I did as it suggested in multiple ways and the error messages keeps showing up. I’ve also shut down the computer, exited and restarted Labview several times and none of this worked. I have included the a picture file below. Where the problem is, is in the producer loop and the error is shown coming out of the DAQ error indicator. One idea I had but I’m unsure how to approach it is to somehow mean the data coming out of the DAQ to reduce what’s getting to the buffer. If anyone knows how to fix this problem please explain it in detail (I mean talk to me like I’m stupid) cause I’ve been stuck on this problem for almost two weeks now. Thank you in advance to anyone who can help.
SteelTiki
Solved!
Go to Solution.

The DAQ error isn't related to your choice of architecture, although your implementation of it might be hurting you. It's almost impossible to follow what's going on in your diagram because you have wires running in many directions (try to keep data flowing from left to right), there are local variables all over the place (almost definitely not needed), and there's a lot of code that's not in the image or is hidden in another frame of the sequence. Normally one would not have the event structure as the consumer loop (as you've done), and it's generally not a good idea to have multiple event structure in the same VI (with rare exceptions usually involving user events). It might not solve your problem but it would be worth taking the time to clean up your diagram. Eliminate sequence structures and local variables as much as possible, move some code into subVIs, and straighten out your wires.
As for the DAQ error: the DAQ board is reading data into a circular buffer, and you're not reading it fast enough, so samples are being overwritten. The reason you're not reading it fast enough is because you only read a single sample at a time (the DAQmx Read is configured for 1 sample on multiple channels) but you say you're acquiring 10,000 samples/second. Since your loop won't run 10,000 times per second, you're not reading all the data, which causes the error. Try configuring the DAQmx Read for multiple samples.

Producer Consumer with a state machine within the consumer

Hi All,
I have been trying to develop a data acquisition system with the producer consumer architecture. To the left of the two main loops I initialize the serial port and any constants and variables im using. I also have an obtain queue VI needed for enqueue and dequeue. Then in the producer loop i have a state machine. The first state is where I wait for a button press on the front panel to write a GO signal on the serial line which will tell the device connected to the serial port to begin sampling data. After this button press I go into the next state which is called my read state.
In the read state I use a property node to read all of the available bytes at the serial port and then enqueue this collected data into a queue. The state machine then is directed to continously go to the read state again and collect more data.
Now this is where my dilemma is...... The consumer loop has the dequeue VI inside it and after this VI i have a state machine (while loop and case structure) which contains the following states
1. Build Array - build an array from the dequeue element and if there is any left over data from the parsing states it will build an array with the left over data and the dequeued data
2. Determine packet type - this state looks for the packet type byte(not necessarily the first byte in the message) and also check the next byte (packet length) to ensure that I am at the begininng of this chunk of data. This state may be a little slow because there can be three different packet types and based on this byte and the packet length it may have to search the array several time to find the valid starting point. This state also determine the next state to go to based on the packet type.
3 packet type 1 parsing - parse data and store the remaining data it leftOver array. Go to exit state.
4 packet type 2 parsing - "" ""
5 packet type 3 parsing - "" ""
6 exit - leave this state machine and fall back to the consumer while loop.
After it exit I think it should fall back to the consumer while loop and dequeue more data and enter the state machine again to build a new array with the dequeued data and leftover data. It seems to work when I trace the execution using the Highlight execution feature, however when I run this all at full speed, it seems to go into the consumers 1st and 2nd states back and forth and not completely go through the state machine.
I tried adding in a delay in the producer loop to give the consumer loop time, but I didnt notice any difference. Is it possible that my dequeue element is retreiving more data while im still in the state machine, causing the execution to leave the state machine before it finished all states?
Is there a better approach to take to solve this problem. Basically I need to read data at a 1,000,000 baudrate and parse it as quickly as possible so that I can break it up into 3 different packet types, write the data to a file, and graph the actual data (header info removed) in realtime. I need to also ensure that I am not losing any of the collected data. Data loss cannnot occur.

A couple of things more to go along with Ben's pointers:
You convert your data from a string, to a U8 array, to a Hex string array in the producer loop, then convert back to a integer to determine what to do with it. In the process, you create two or three copies of your data, slowing yourself down quite a bit. The code would be quite a bit more efficient if you left the data as a U8 array. You can change the format of the controls and indicators to show hex values instead of integer by right clicking on them and selecting Format and Precision...
Your search code is fairly inefficient. I made a whack at making it a bit better. See attachment below.
If you continue to run into race conditions, you can debug them using a calls to the Windows debug write sprinkled liberally about your code. Check out the post here for more information.
Don't let your lack of format LabVIEW training stop you. The biggest thing to get is the data flow paradigm (aka data is wires, not registers). Once you get past that and learn how to pass data around using shift registers, queues, events, etc, you are most of the way to mastering LabVIEW. The rest is just learning the plethora of functionality LabVIEW gives you (yes, I have reimplemented LabVIEW native code more than once in the process of learning).
Let us know if you need more help.
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Attachments:
serialUtil_V3_DFG.zip ‏137 KB

Producer/Consumer Help

I have created this labview code called '2D Fit.VI' without any DAQ hardware that will create a mutlidimensional fit, is it possible to put this VI in a Producer/Consumer format? If so how would I approach it? The VI's are attached below.
Thanks.
Attachments:
Multidimensional Fit.zip ‏170 KB

ytran wrote:
I have created this labview code called '2D Fit.VI' without any DAQ hardware that will create a mutlidimensional fit, is it possible to put this VI in a Producer/Consumer format? If so how would I approach it? The VI's are attached below.
Thanks.
I assume you have already read the white paper on Producer/Consumer. I would start by turning the code inside of the event structure into a subVI. I will be a lot easier to move around then.
Then you just make a queue that can hold new data and read the queue in the consumer loop. Give it a try first and then post what you have. We can help you a lot more from there.
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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 & 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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Still stuck with the same old producer consumer weight problem need help

Hello All,
This is the problem I am stuck with right now.
I have two array lists one producer array list and one consumer array list denoted by a and b
P1 P2 P3 P4 P5
5 6 7 8 9
C1 C2 C3 C4 C5
2 3 4 5 6
Now we find all those producer consumer pairs which satisfy the criteria Pi>=Ci
We have the following sets
(5,2)(6,2)(7,2),(8,2),(9,2)
(5,3)(6,3)(7,3),(8,3),(9,3)
(5,4)(6,4)(7,4),(8,4),(9,4)
(5,5)(6,5)(7,5),(8,5),(9,5)
(6,6)(7,6)(8,6),(9,6)
Let us done each of them with Si
so we have S1,S2,S3,S4,S5
we assign a third parameter called weight to each element in Si which has satisfied the condition Pi>=Ci;
so we we will have
(5,2,ai),(6,2,bi),(7,2,ci)....etc for S1
similarly for S2 and so on.
We need to find in each set Si the the pair which has the smallest weight.
if we have (5,2,3) and (6,2,4) then 5,2,3 should be chosen.We should make sure that there is only one pair in every set which is finally chosen on the basis of weight.
Suppose we get a pair (5,2,3) in S1 and (5,2,3) in S2 we should see that (5,2,3) is not used to compare to compare with any other elements in the same set S2,
Finally we should arrive at the best element pair in each set.They should be non repeating in other sets.
Given a problem
P0 P1 P2 P3 P4
9 5 2 2 8
6 5 4 5 3
C0 C1 C2 C3 C4
we have So as (P0,C0) and (P4,C0)
assuming that the one with the smaller index has lesser weight PO is selected.In the program I have used random weights.from set S1 we select the pair PO,CO
S1 =(P0,C1),(P1,C1) and (P4,C1)
since P0 and P4 are already used in previous set we dont use them for checking in S1 so we have (P1,C1) as best.
S2=(P0,C2),(P1,C2) and (P4,C2) so we dont use P0,C2 and P1 and C2 because PO and P1 are already used in S1.
So we choose P4,C2
in S3 and S4 ae have (P0,C3),(P1,C3),(P4,C3) so we dont choose anything
and same in S4 also.
So answer is
(P0,C0),(P1,C1) and (P4,C2).
My program is trying to assign weights and I am trying to print the weights along with the sets.It doesnt work fine.I need help to write this program to do this.
Thanks.
Regards.
NP
What I have tried till now.
I have one more question could you help me with this.
I have an array list of this form.
package mypackage1;
import java.util.*;
public class DD
private int P;
private int C;
private int weight;
public void set_p(int P1)
P=P1;
public void set_c(int C1)
C=C1;
public void set_weight(int W1)
weight=W1;
public int get_p()
return P;
public int get_c()
return C;
public int get_x()
return weight;
public static void main(String args[])
ArrayList a=new ArrayList();
ArrayList min_weights_int=new ArrayList();
ArrayList rows=new ArrayList();
ArrayList temp=new ArrayList();
Hashtable h=new Hashtable();
String v;
int o=0;
DD[] d=new DD[5];
for(int i=0;i<4;i++)
d=new DD();
for(int i=0;i<4;i++)
d[i].set_p(((int)(StrictMath.random()*10 + 1)));
d[i].set_c((int)(StrictMath.random()*10 + 1));
d[i].set_weight(0);
System.out.println("Producers");
for(int i=0;i<4;i++)
System.out.println(d[i].get_p());
System.out.println("Consumers");
for(int i=0;i<4;i++)
System.out.println(d[i].get_c());
System.out.println("Weights");
for(int i=0;i<4;i++)
System.out.println(d[i].get_x());
for(int i=0;i<4;i++ )
int bi =d[i].get_c();
ArrayList row=new ArrayList();
for(int j=0;j<4;j++)
if( d[j].get_p() >=bi)
d[j].set_weight((int)(StrictMath.random()*10 + 1));
row.add("(" + bi + "," + d[j].get_p() + "," +d[j].get_x() + ")");
else
d[j].set_weight(0);
row.add("null");
rows.add(row);
System.out.println(rows);
int f=0;
for(Iterator p=rows.iterator();p.hasNext();)
temp=(ArrayList)p.next();
String S="S" +f;
h.put(S,temp);
String tt=new String();
for(int j=0;j<4;j++)
if(temp.get(j).toString() !="null")
// System.out.println("In if loop");
//System.out.println(temp.get(j).toString());
String l=temp.get(j).toString();
System.out.println(l);
//System.out.println("Comma matches" + l.lastIndexOf(","));
//System.out.println(min_weights);
f++;
for(Enumeration e=h.keys();e.hasMoreElements();)
//System.out.println("I am here");
int ii=0;
int smallest=0;
String key=(String)e.nextElement();
System.out.println("key=" + key);
temp=(ArrayList)h.get(key);
System.out.println("Array List" + temp);
for( int j=0;j<4;j++)
String l=(temp.get(j).toString());
if(l!="null")
System.out.println("l=" +l);
[\code]

In your example you selected the pair with the greatest
distance from the first set, and the pair with the least
distance from the second. I don't see how the distance
function was used.
Also it's not clear to me that there is always a solution,
and, if there is, whether consistently choosing the
furthest or the closest pairs will always work.
The most obvious approach is to systematically try
all possibilities until the answer is reached, or there
are no possibilities left. This means backtracking whenever
a point is reached where you cannot continue. In this case
backtrack one step and try another possibility at this
step. After all possible choices of the previous step,
backtrack one more step and so on.
This seems rather involved, and it probably is.
Interestingly, if you know Prolog, it is ridiculously
easy because Prolog does all the backtracking for you.
In Java, you can implement the algorithm in much the same
way as Prolog implementations do it--keep a list of all the
choice points and work through them until success or there
are none left.
If you do know Prolog, you could generate lots of random
problems and see if there is always a solution.

Producer consumer timing

Back again
Thought I was getting somewhere now I am at another brick wall.
Bit of background:
I have a producer consumer set up. In the producer loop there are 2 DAQmx read VI's reading from a Pressure task and a Temperature task. These are multiple channels, 1 sample, outputtng a 1D wave form. This loop is set to run every 20ms. The two tasks were created using DAQmx Create Channel VI's and DAQmx Start Task VI's. The producer loop feeds a display on the front panel with the sensor values and this hopefully is refreshed at the 50Hz I have asked for. Secondly the loop bundles up the waveforms and puts them in a queue where they are picked up for logging by the consumer loop. In the consumer loop I have a wait 1000ms timer and a Write to Measurment File Express VI to do the logging. This is supposed to log at 1 per second.
The queue is set to enqueue at opposite end, and the max queue length is set to 1. I.E. I only want to log the value at that specific second, but I want to show the data on the front panel at 50 times a second.
Now heres my problems:
1) I replaced the DAQmx Create channel's with a MAX project task wired into my DAQmx Start Task VI. As expected the thing picks up and displays the sensor values as it did before. However there is now a problem logging. Before when I had the DAQmx Create Channel, the logging recorded my values correctly at 1 second intervals. The time stamp in the X column went up by 1 second for each set of results. But now, with the MAX project task (needed because of custom scales and differing min/max values for different sensors), The logging still seems to happen at 1 per second, but the time stamp intervals are the same as the sampling rate set in the task!!! (ie at 50Hz the time stamp goes up 20ms for each result even though the results are being recorded at 1 per second)
2) The timing just seems out of whack.
I keep getting errors that the requested data no longer exists, that it was there but then was over written. Increasing the buffer size or sampling rate is supposed to remedy this... but what sampling rate? the rate set in the task? or the loop iteration speed? I dont understand.
Secondly, despite telling my consumer loop to wait one second between picking up stuff out of the queue to log, it seems to be going round nearly the same pace as the producer loop. To top this off the producer isnt going round at the speed I asked it too either! I put indicators on the loop counters to see this. they are going round at maybe 2Hz.
I have included my VI's
What am I doing wrong, its really bugging the crap out of me!
Attachments:
EngineMon.zip ‏90 KB

The reason you would use get time and date in seconds to to ensure that you log every second. If you use the 1 second wait then you do not take into account the exicution time of your loop. If you add more to the loop in the future than you will see that you do not log every second as you thought. If you loop took 500ms to exicute and you have the 1000ms wait then the actual excution time for recoding to file is 1.5 seconds not 1000ms as you desired. The way I did it will always give you one second unless you exicution time for your loop exceeds one second.''
I did make one change to the vi. I shoulod have put the write in the true false case so that the write only happens when the 1 second has expired.
Tim
Johnson Controls
Holland Michigan
Attachments:
VDU3.vi ‏59 KB

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

Running subVI in parallel with itself using producer-consumer pattern

I'm using the procuder-consumer pattern to create what I call threads in response to various events much like in Producer Consumer with Event Structure and Queues
I have several physical instruments, and would like to run the exact
same test in parallel on each of the instruments. I have a subVI
that takes as inputs a VISA resource and a few control references among
other things and then performs the desired experiment. I have a
separate consumer loop for each physical instrument, with this subVI
inside each consumer loop.
My test VI worked great; each consumer loop was a simple while loop
incrementing a numeric indicator (not using my real subVI above).
However, my real program can only run one consumer loop at a time much
to my dismay. Reworking my simple test VI to use a subVI to
increment the indicator rather than just explicitly coding everything
resulted in the same problem: only a single consumer loop ran at a time
(and as I stopped the running loop, another would get a chance to
begin). The subVI in this case was extremely
simple taking only a ref to the indicator and a ref to a boolean to
stop, and incrementing the indicator in a while-loop.
Is there a way around this? Now that I've spent the time making a
nice subVI to do the entire experiment on on the physical instrument, I
thought it would be fairly trivial to extend this to control multiple
instruments performing the same experiment in parallel. It seems
only one instance of a given subVI may run at one time. Is this
true? If it is indeed true, what other options do I have? I
have little desire to recode my subVI to manually handle multiple
physical instruments; this would also result in a loss of functionality
as all parallel experiments would run more or less in lock step without
much more complexity.
Thank you.

You need to make your subvi reentrant. Then it can run several instances at any time with each instance occupying its own unique memory space. Click on File - VI Properties - Execution, and check the reentry execution checkbox. Then save the vi.
- tbob
Inventor of the WORM Global

Producer/Consumer Architecture

Hello All,
I am currently working on an application using State Machine Architecture where I have to monitor various parameters (7 temperature values & 3 pressure values), along with this I have to On/Off a Clutch using a digital Output for set time (e.g. On for "X" seconds OFF for "Y" seconds), but as soon as the pressure and temperature values go beyond upper or lower limits or whenever the user presses the Emergency Stop (that means I have to monitor Digital Input as well) so I am moving to different error cases depending on which values go beyond limits or emregency pressed etc..
But this realisation is not working fine as I have to monitor and control several other things in addition to acquiring data....till now I just have used State Machine Architecture, I have seen Producer/Consumer Template but not quite sure how to realise such kind of application which involves data acquisition along with user interaction and monitoring.
Could someone please put some light on giving similar kind of example or what else I can try with this problem.
Regards
James

Hello James,
A Producer/Consumer architecture will certainly do the trick for you. I am sending you an example that has the Data Acquisition section in the producer loop. However, you can also put your User Interface in the Producer loop and have the Data Acquisition in the Consumer loop. The Queues are used for sending data from the Producer to the Consumer(s) loop(s) (you can have multiple comsumer loops).
You will just have to design specific cases to react to different user inputs.
By the way, this example is from LabVIEW Basics II training course. If you have never taken LabVIEW Basics I and II, I highly recommend them. You can self-pace the class or take it with an instructor.
LabVIEW Courses
Hope this helps!
Message Edited by Kalin T on 03-23-2007 09:57 AM
Kalin T.
National Instruments
Attachments:
ImplementedProducerConsumer.zip ‏250 KB

What is ment by 'producer/​consumer approach'?

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What is ment by 'producer/consumer approach'?