LabVIEW array performance: Two loops operating on the same massive array

Yes there has been a lot said and left unsaid about LabVIEW performance in the past - but I have to ask the following:
Is it possible to have two seperate while loops act on the same data without making copies?
Say I have a 1GB array of doubles which I have wired to a shift register on one loop. With a little bit of effort (by using in-place and chasing the dots a bit) it would be possible to operate on that data inside that loop without making copies.
But what if I need to also access that same array in a different loop (which is running at a different rate). I basically need two loops' shift registers to point to the same data. At the moment the only way I can manage this is to use DLL calls which destroys dataflow but al least makes no copies. It also means I cannot use LabVIEW code but have to resort to C coding.
Data corruption is no issue as the two loops, at any instant, operate in different locations of the array.
Any smart ideas that will work?

drclaw wrote:
Hi AnthonV,
A Functional Global approach might suit your needs. This will allow you to keep you data in a shift register, but access/modify parts of the data from other VIs or loops.
Another option is to use a single element queue to store the array to achieve a similar result.
Both these options and more techniques are located at
http://zone.ni.com/devzone/cda/tut/p/id/3625#toc0
Hope that helps
Good suggestion. Functional Globals also go by the name "Action Engine" as I discuss in this Nugget on Action Engines.
Put all of your number crunching code inside appropriately named Actions of the AE and that way all of the work CAN be done "in-place".
Have fun!
Ben
Ben Rayner
I am currently active on.. MainStream Preppers
Rayner's Ridge is under construction

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Performing two NiDAQ operations at once...

Hello,
I am using NiDAQ 7.1 and a 6025E DAQ.
I am performing a simple rocket engine test.
These are my concerns so far...
1. The NiDAQ board cannot perform two operations simultaneously. What this means is that in order to operate the valve (digital out), I would have to interrupt the continous analog input scanning. This would cause a problem. I would not be recording analog inputs during, or immediately after the operation of the valve (digital out).
2. Synchronizing the operation of the valve with the continous analog input data recording. i.e What sample point in the analog input data corresponds to the instant the valve was opened/closed? I am using an accelerometer to record when the valve opens/closes.
But the interruption of operating the valve will render it useless since analog input recording will have been halted, and thus the accelerometer data will not have been recorded.
How do I operate the valve at the same time that I am continously reading analog inputs? According to your documentation, it is not possible to perform two operations on the E series at the same time. How do I overcome this issue? My analog input sampling frequency is 2KHz.
Would something like this work:
SCAN_Op(length of time before opening valve)
DIG_Line_Out(Turn on valve)
SCAN_Op(length of time before closing valve)
DIG_Line_Out(Turn off valve)
SCAN_Op(length of time to record after valve is closed)
StoreSamplesToFile()
What is the amount of time between SCAN_Op() returning, calling DIG_OUT_Line() and calling SCAN_Op()? i.e. how many samples will I miss due to stopping and starting analog input recording using SCAN_Op()?
- Tree

Hey Tree,
I think you are still slightly confused on what Traditional NI-DAQ is capable of doing. The E-Series device is capable of doing analog input, analog output, digital input, digital output, and counter operations all at the same time. The problem with the Traditional NI-DAQ driver (not DAQmx) is that it is not a truly multithreaded driver.
Now what does this mean?
Assume you have two threads operating at the same time. One is performing an analog input and the other is performing a digital output. If the analog input thread is executing the AI_Read function then it is waiting for the device to fill the buffer with the number of samples that you have requested and then it will return the array of data to your program.
If the Dig_Out_Lin
e function tries to execute while the AI_Read is waiting for the data then the DIG_Out_Line function will be blocked until the AI_Read completes. You can minimize the effect by reading smaller chunks of data or placing small wait functions in your analog input while loop so the processor and driver can perform other tasks.
This will not change the analog input process and you will not miss any data points if you have it configured for a continuous analog input. The data is always being transferred from the DAQ device to the buffer. You are just reading from that buffer when you execute the read functions.
The best solution to your problem would be to use NI-DAQmx. This driver is multithreaded and the analog input will not block the digital output thread. There should be several examples that are installed for ANSI C on your hard driver at C:\Program Files\National Instruments\NI-DAQ\DAQmx ANSI C Dev.
I hope this helps out.
Joshua P.
Application Engineering
National I
nstruments

Writing LabVIEW measurements of two loops (Charge cycle and discharge cycle) in one file

Hey,
I was wondering if it is possible to write Labview measurements from two loops (Stacked Sequence Structure) into one file. Currently, it is writing the charging data in one file and discharging data in one file. I have to combine the data everytime to graph the charge and discharge cycles and sometimes there's about 50 cycles and copying and pasting does take up lot of time.
I'll try to upload my vi in a bit
Solved!
Go to Solution.

Hey Mike,
I'm very new to Labview, could you please show an example.
btw, I attached my vi and I didn't build it
Message Edited by Support on 07-15-2009 11:27 AM

ERROR: MyService.jws:715:There are two or more operations with the same schema-element 'ns0:MyNameSpace' on the input message in a web service file or callback interface.

I have two web service operations that have the same complex type as their input
parameter. I want to map this type to an existing schema. I can successfully
do this with the first operation using XQuery but when I attempt to do this with
the second operation I get the following error:
ERROR: MyService.jws:715:There are two or more operations with the same schema-element
'ns0:MyNamespace' on the input message in a web service file or callback interface.
ERROR: SUGGESTION: Use different schema-element values for each of those operations.
How can I use different schema-element values? The input parameters are to be
mapped to the same schema and same element since they are the same for both operations....

I am having the same problem. How did you resolve this..?? could you please tell me the solution??
Thanks
Shari

[svn:fx-trunk] 10214: This fixes the problem that if two text components share the same textFlow there is an infinite loop involving updateDisplayList - damageHandler - invalidateDisplaylist - back to updateDisplayList.

Revision: 10214
Author:   [email protected]
Date:     2009-09-13 07:33:58 -0700 (Sun, 13 Sep 2009)
Log Message:
This fixes the problem that if two text components share the same textFlow there is an infinite loop involving updateDisplayList -> damageHandler -> invalidateDisplaylist -> back to updateDisplayList. The bug file was for TextArea which is RET but the same bug was in RichText as well.
This example with a renderer exposed it because the typicalItem that is composed to figure out sizes and the actual first item in the list share the same textFlow. It actually has nothing to do with useVirtualDisplay other than it was sharing a textFlow.
It turns out that the TextFlowFactory dispatches damage events every time the textFlow is composed. Unlike when the flowComposer is used, it always considers the flow damaged. It was exacerbated by each of the two components having a damage handler for the same textFlow.
The solution is to use the textFlow generation number. In the damageHandler if the generation is the last known generation number, assume no changes, and return immediately from the damage handler.
QE notes: There are 1 TextArea, 6 TextInput and 2 NumericStepper failuers, with or without my changes. The common link seems to be DispatchKeyEvent. Most were testing maxChar, displayAsPassword and restrict. I tested these and they seem to be working correctly.
Doc notes:
Bugs: SDK-23002
Reviewer: Gordon
Tests run: checkintests, TextArea, TextInput and NumericStepper
Is noteworthy for integration: no
Ticket Links:
    http://bugs.adobe.com/jira/browse/SDK-23002
Modified Paths:
    flex/sdk/trunk/frameworks/projects/spark/src/spark/components/RichEditableText.as
    flex/sdk/trunk/frameworks/projects/spark/src/spark/components/RichText.as
    flex/sdk/trunk/frameworks/projects/spark/src/spark/components/supportClasses/RichEditable TextContainerManager.as

Revision: 10214
Author:   [email protected]
Date:     2009-09-13 07:33:58 -0700 (Sun, 13 Sep 2009)
Log Message:
This fixes the problem that if two text components share the same textFlow there is an infinite loop involving updateDisplayList -> damageHandler -> invalidateDisplaylist -> back to updateDisplayList. The bug file was for TextArea which is RET but the same bug was in RichText as well.
This example with a renderer exposed it because the typicalItem that is composed to figure out sizes and the actual first item in the list share the same textFlow. It actually has nothing to do with useVirtualDisplay other than it was sharing a textFlow.
It turns out that the TextFlowFactory dispatches damage events every time the textFlow is composed. Unlike when the flowComposer is used, it always considers the flow damaged. It was exacerbated by each of the two components having a damage handler for the same textFlow.
The solution is to use the textFlow generation number. In the damageHandler if the generation is the last known generation number, assume no changes, and return immediately from the damage handler.
QE notes: There are 1 TextArea, 6 TextInput and 2 NumericStepper failuers, with or without my changes. The common link seems to be DispatchKeyEvent. Most were testing maxChar, displayAsPassword and restrict. I tested these and they seem to be working correctly.
Doc notes:
Bugs: SDK-23002
Reviewer: Gordon
Tests run: checkintests, TextArea, TextInput and NumericStepper
Is noteworthy for integration: no
Ticket Links:
    http://bugs.adobe.com/jira/browse/SDK-23002
Modified Paths:
    flex/sdk/trunk/frameworks/projects/spark/src/spark/components/RichEditableText.as
    flex/sdk/trunk/frameworks/projects/spark/src/spark/components/RichText.as
    flex/sdk/trunk/frameworks/projects/spark/src/spark/components/supportClasses/RichEditable TextContainerManager.as

Why does a LabVIEW executable generate two taskbar buttons on the taskbar?

When a LabVIEW executable is run, it generate two taskbar buttons (with the same name) in the task bar each of them pointing to the same window (panel). Is there a way to prevent it from creating two buttons?
thanks
~Vipin

viper 159 wrote:
When a LabVIEW executable is run, it generate two taskbar buttons (with the same name) in the task bar each of them pointing to the same window (panel). Is there a way to prevent it from creating two buttons?
Add the following line to your executable's .ini file
HideRootWindow=True
There's a KnowledgeBase item here.
=====================================================
Fading out. " ... J. Arthur Rank on gong."

HT1311 Can two iTunes accounts be operated from the same user address?

I have purchased an ipad2 and when I synced it on itunes it automatically synced all of my wife's music. Can I unsync her music? Can I have two ITunes accounts on the same username?

Hello, Welcome to discussions. More information about this can be found below.
You can authorize your account on up to a total of 5 computers. So your account can be authorized on 5 machines, and her account can be authorized on 5 machines. So yes a computer is capable of having more then 1 account authorized on it.
About iTunes Store authorization and deauthorization
http://support.apple.com/kb/HT1420
If you share a computer. You will want to ensure you sign out of your iTunes Store account before the next person uses iTunes. This will prevent accidental charges on someone else's Apple ID.
Or you can create a second Windows User account, each have your own user account, own iTunes, and purchases and content will be separate.

Java synchronization mechanism allows two threads to hold the same lock?

Dear all,
I am a little bit puzzled since I cannot explain why I get the following behavior.
I have a small Java program to draw components. The drawings are cached in the memory for performance improvements. The cache is access by two different threads. Now the funny thing: even I synchronized every access to the cache, I still get ConcurrentModificationExceptions.
Here is a part of the code:
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Now my question is why do I get java.util.ConcurrentModificationException, especially in situations where a lot of repaintings have to be done and the window is resized? When I remove the caching stuff, everything works perfect, but only a little bit slow.
Thanks for any help.

In your elementUpdated method, you are using an Iterator to walk over the set of keys in your map. You can't see the Iterator, because you are using the new for-each loop syntax which hides it from you - but it's there under the covers. You are then removing elements from your map directly. This is what causes your ConcurrentModificationException.
You should re-write your loop to explicitly use an iterator, and then do your remove operation through the iterator.
Incidentally, you have a slight race condition in your paint method. Two (or more) threads could simultaneously discover that a given image is not cached, then both draw it, then both cache it. If the drawing operation produces the same drawing every time, then the only problem this causes is the overhead of drawing the image multiple times. To fix this, wrap the get, draw and put operations in a single synchronized block.

I have written a binary file with a specific header format in LABVIEW 8.6 and tried to Read the same Data File, Using LABVIEW 7.1.Here i Found some difficulty.Is there any way to Read the Data File(of LABVIEW 8.6), Using LABVIEW 7.1?

I have written a binary file with a specific header format in LABVIEW 8.6 and tried to Read the same Data File, Using LABVIEW 7.1.Here i Found some difficulty.Is there any way to Read the Data File(of LABVIEW 8.6), Using LABVIEW 7.1?

I can think of two possible stumbling blocks:
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LabVIEW Champion . Do more with less code and in less time .

Will interlocked operation only prevent other interlocked operation on the same location or any visit to the same location?

when reading
https://msdn.microsoft.com/en-us/magazine/cc163715.aspx , i found the following statement:
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"However, i am not sure whether other threads can read that object during the interlocked operation? If they can, how can i prevent them?"
If I understand correctly you're trying to lazy initialize a variable.
Why aren't you using Lazy<T> to begin with, it does exactly what you want if you use LazyThreadSafetyMode.PublicationOnly.
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If the thread that doesn't use interlocked to read the object variable gets a non-null reference then it means that the initialization of the object was done, otherwise it couldn't have got a non-null reference in the first place.
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while (object == null) { ... }
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Share iTunes purchases between two user accounts on the same Mac?

I have a Macbook Pro, for my bride and I, and a Macbook, for our kids. Both Macs are authorized on my iTunes account.
So, how can I share an iTunes Store purchased song on my account with my wife's? I understand how to turn on sharing and she can see my songs in iTunes on her account, but she cannot synch them to her iPod.
Now, I'm allowed to authorize an iTunes account on up to five Macs. I have two. But I have four accounts. Either way, I won't be exceeding five copies, but can't find a way to get a song I bought in my iTunes to my wife's iPod.
We use the same iTunes account but don't want to have to buy things twice to get them on her iPod. Just seems weird that I could put it on five machines but not two user accounts on the same one.
Message was edited by: Sky Guy

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Two different Resultsets for the same query (running at the same time)

I am using the Thin Driver for Oracle 8.1.6. I am invoking queries in multithreading mode (each thread has his own connection to the oracle DB). If i am invoking the same SQL-Statement in two different threads nearly at the same time, only the ResultSet of the first query is complete. The ResultSet of the second query is not complete (the number of tuples differs each time I run the program). Principally the two ResultSets should be the same (no changes are done at the same time in the DB), but they are not.
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I hope anybody can help me.

Pranav,
As this BADI is having option checked 'Multiple use'. You can implement multiple implementations.
You need not to deactivate the existing implementation.
Reddy

I am trying to store music for two different iPods on the same computer, against two different Apple IDs. When I try and download content from the Cloud I get an error message?

I am trying to store music for two different iPods on the same Windows 8 computer, and when I try and download content from the Cloud I get an error message. Is it possible to have two different Apple IDs on the same computer?

Unfortunately you've discovered too late how important it is to maintain an up-to-date backup of your iTunes library (and all other data of value). You could, before wiping the drive, have considered making use of a commercial data recovery service that could (albeit at considerable cost) have extracted your library from the hard disk, even if virus infected.
In the absence of that option, you will need to restore the content of your library from its original sources:
Depending on your location, you may be able to re-download any iTunes Store purchases that are still available on the Store
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The specific situation that you describe regarding the music imported from your friend's external HDD suggests that either the source is badly organized and/or originates from a source other than iTunes (other media players may use alternative tags for information like artist, title, album, etc. that are not wholly consistent with how iTunes handle these). Without details of the issues you're seeing it is difficult to suggest a remedy other than going through the media album-by-album, track-by-track, and correcting the inconsistencies.
In the absence of a backup or access to the original library data there is no option other than painstakingly recreating your library as described above. As you do so, you'll now realize how important creating and maintaining backups are - in my case I have at all times three separate duplicates of my library, in two different locations, where none is ever more than a week old compared to the content of my master library.

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Hi,
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Also, the process you are using for testing obviously could not overwrite datamembers (or registers if you will) that would interfere in the overall application, in other words you can test your application as long as you keep the coherency of the test.
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It should work in any version of Java as long as the server socket factories are null or equal according to Object.equals() or its override in the SSF.equals() method if any. Which needs to be present and needs to take the form:
public boolean equals(Object object)
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}with further tests if the server socket factories have additional state.

LabVIEW array performance: Two loops operating on the same massive array

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