TCP Open Briefly hangs LabVIEW

Hello LabVIEW forum! Long time no see. I have been away from LabVIEW doing other things but.... I'm back.
Background:
I am working on a project where I need to make a TCP connection to a Windows 7 machine. The Windows machine will intentionally reboot for each test. When it boots i need to make a TCP connection to a server that automatically starts on the Windows machine and send some commands. While it is booting, I try to connect, get an error, try again, etc until the connection is made.
The problem:
This machine name is not resolved by DNS or the hosts file. If I try to connect using a host name, and the host name cannot be resolved, LabVIEW will freeze for a few seconds. If I click the red abort button I get the not responding error. It will eventually recover and give me an error 54. The timeout is not relevant in this situation. It doesn't matter how long or how short I set it to, it always hangs LabVIEW for about three to five seconds. If I try to connect by IP number instead, then I don't see this problem. If the machine is off I just get a timeout error but LabVIEW doesn't freeze.
I cannot post code but try this: Write a VI with an infinite while loop and an indicator connected to the i terminal and place a 100mS delay in it. Run that and notice that the number increments. Now create and run a second VI with the TCP open in it and use a machine name that does not exist. What I see is that the number in the first VI will quit incrementing. I am using LabVIEW 2014 32 bit on Windows 7 Ultimate 64 bit. First open a console and try to ping the non-existant name you are trying to connect to and verify that it doesn't print an ip number. Some Internet providers will resolve all non existant hostnames to an IP they own for their own gain. If that is the case then you will not be able to duplicate this bug.
I have a workaround (put an entry in my hosts file) but I thought I would mention this possible bug. Plus it gives me an opportunity to say hi to all my old friends on my favorite fourm! (the list is long but you know who you are)
=====================
LabVIEW 2012
Solved!
Go to Solution.

LabVIEW calls Winsock for all network operations. Most of the Winsock operations are synchronous. This is not a big problem for most of LabVIEW code as LabVIEW is multithreading and executes the nodes in whatever thread the current VI is at. However some functions need to access some global data space and are protected by some means. This can be a global mutex and sometimes it's also solved by forcing the node to always execute in the UI thread of LabVIEW which also executes the windows message loop and Winsock does hook into that message loop to do its own internal pseudo synchronous operation.
The check for Adres to IP is something you can try. It may also lock up because of the internal Winsock hooking into the application message loop, but maybe it won't so that you can circumvent the problem. There is no way for an applciation using the normal Winsock API to avoid internal Winsock timeouts for synchronous functions, and the adress resolutino API does not really support asynchonous variants.
Rolf Kalbermatter
CIT Engineering Netherlands
a division of Test & Measurement Solutions

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Labview: TCp Open Issue!

Hi Everyone,
I'm working on a MODBUS routine for communication with one of our control modules. I'm using NI's Modbus library to initiate a connection, check the registers, etc then report the results back to a teststand seq for fruther analysis.
Problem? I made a few minor adjustments to the library (just the main routine) because i only need to read the registers for now. However, when I conenct with the TCP Open Connection, nothing happens. Well, not completely true.. I sinffed the connection with Ethereal and I get the following errors...
1)
SENDING:
TCP: Src Port 2061, Dst Port: 502, Seq: 13, Ack: 10 , Len:12
Checksum: 02x282d [incorrect, should be 0xfd6b]
2)
RECEIVING:
Modbus/TCP:
-Modbus: Function 4: Read input registers. Exception: Illegal data address
exception code: Illegal data address (2).
I understand the second one and believe it's related to the first but ....?
Does anyone have any ideas or suggestions? I'd go into the TCP OPEN.vi if I could, but it wont let me, so...?
Thanks Again,
BK

Hi BK576,
Does this still give you problems if you don't make your modifications
to the MODBUS libraries? What changes were made? Could you possibly
submit an NI-Spy capture taken while seeing this error?
Regards,
Matt S.
LabVIEW Integration Engineer with experience in LabVIEW Real-Time, LabVIEW FPGA, DAQ, Machine Vision, as well as C/C++. CLAD, working on CLD and CLA.

Using SMTP I can not use a mail server with more than 13 characters. I get an error from TCP open

I have no trouble sending an email if the mail server name is less than 13 characters long. I get an error 54 from TCP open when it exceeds that length. How do I get around this?

Don't know what to say, I just tried the SMTP email VI I have with an 18-character mail server address and everything worked fine. The error 54 means that the address is ill-formed.
The only thing I would suggest is trace the mail-server address down through the hierarchy and make sure nothing is done to modify it. Also try putting a probe on the wire going into the TCP open function and make sure the string you see there is the same one you are using. Finally, change the formatting of the control taking the address into the subvi that contains the TCP open function (SMTP Open Session.vi)to show the slash codes and make sure some invisible characters aren't getting added along the way.
As a last resort save the vi in 6.0 format and send it to me and I'll
try it on my system--maybe there's something screwy going on with your computer...
Mike...
Certified Professional Instructor
Certified LabVIEW Architect
LabVIEW Champion
"... after all, He's not a tame lion..."
Be thinking ahead and mark your dance card for NI Week 2015 now: TS 6139 - Object Oriented First Steps

Bug? SMTP send hangs LabVIEW

I am trying to send an email during an alarm state using the SMTP VIs included with LabVIEW (2013, have not tested 2012). It seems that the SMTP send VI hangs LabVIEW while it is running to the point that my software doesn't start shutting down because LabVIEW is waiting for SMTP send.
SMTP send is running parallel to everything else, so it shouldn't cause a hang just because it hasn't finished running. The UI stops redrawing (i.e. if I open a window in front of the program and close it, LabVIEW doesn't redraw the front panel - I still see the old window), every parallel process in the code stops running, and the cursor changes to the busy cursor while it works away.
Today at my office, this delay is 3-5 seconds. Last week when testing at my customer, the delay was 20-30 seconds. The email always gets sent, but it seems while it is logging into the mail server and doing whatever transactions are necessary, LabVIEW is non-responsive.
Please note I am sending a 1-2 sentence email with no attachments. I am not use SLL/TLS, although my server does require a username and password login.
Is anyone else seeign this?
Thanks,
Matthew

Joel,
Same behavior. As I noted in my original post, it locks up at send. If you have a fast connection to your server and are sending a short messsage, you may not see it. My server has a delay for loggin in and it is not internal, so it takes 5 seconds or so for it to login, and send the email. During that time, LabVIEW is non-responsive.
If you have a quick connection, you may need to try using the vi that sends attachments so the session with the server lasts longer.
The issue is specifically with vi.lib\smtpClient\Send.vi. It is password protected, so I cannot determine exactly what is locking up, but it is in there.
For now, I found an example on the forums that is not very robust, but got me through the immediate problem. It can send an email without locking up LabVIEW, so I know NI's code is doing something it probably shouldn't be.
Matthew

DLL Hangs LabView

Here is a twist to the problem of a DLL hanging LabView. Our development group sent me a set of vi's that call C functions from a DLL. When I try to open the vi's LabView hangs. I had the vi's changed so the 'Specify path on diagram' was checked. This resolved the problem of the vi's opening. Only problem is they wouldn't run when downloaded to PXI target running LabView RT. Now for the interesting twist. I kept trying to run the vi's with the 'Specify path on diagram' box checked but I never had any luck getting them to run. I then went back to original vi's ('Specify path on diagram' not checked) and they would now load and not hang LabView. On top of that, they downloaded to the target and executed without any problems.
My question is what could changed in Labview? I didn't change any options or any parameters in the .ini file. I am trying to run the same vi's on a second machine and I'm having the DLL hang problem on that machine. Again, I've compared .ini files and LabView options and there are no differences. Any ideas?
Thanks!

AIM-USA wrote:
Here is a twist to the problem of a DLL hanging LabView. Our development group sent me a set of vi's that call C functions from a DLL. When I try to open the vi's LabView hangs. I had the vi's changed so the 'Specify path on diagram' was checked. This resolved the problem of the vi's opening. Only problem is they wouldn't run when downloaded to PXI target running LabView RT. Now for the interesting twist. I kept trying to run the vi's with the 'Specify path on diagram' box checked but I never had any luck getting them to run. I then went back to original vi's ('Specify path on diagram' not checked) and they would now load and not hang LabView. On top of that, they downloaded to the target and executed without any problems.
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Thanks!
LabVIEW ini files and options have little to do with such kind of problems. It is most likely something the DLL in question tries to do on loading, that is causing this problem. A possibilitiy is that it is using C runtime libraries that are not present on the target system. If the DLL was compiled with VS 2005 it will almost always reference the mscvr70.dll or similar DLLs unless you go to great lengths when compiling and linking that DLL. Now are these Visual C runtime libraries sometimes standard part of Windows but seldom of a non MS OS like the RT targets are. Also the VS 2005 runtime libraries aren't delivered with Windows XP and older (not sure about Vista) so need to be installed from the Visual C Distributables Installer (but this will likely not work on RT systems since those runtime libraries have again dependencies on (privat and undocumented) functions in the Windows kernel.
Now if it would be just a simple dependency you should get an error when trying to dynamically load that DLL ('Specify path on diagram' checked) or an error box telling you that the DLL in question could not be found (when unchecked). The error is sligthly misleading since the DLL itself could be found but LabVIEW was not able to load it into memory since Windows refused to load it into memory because of missing dependancies.
The fact that loading the DLL does hang LabVIEW makes me guess that the DLL in question does try to do some magic in it's own loading function (DLL_PROCESS_ATTACH) and hangs in there because of missing Windows components or something.
This goes deep into Windows internals and without seeing the source code of the DLL in question it is almost impossible to give more detailed advice.
Rolf Kalbermatter
Rolf Kalbermatter
CIT Engineering Netherlands
a division of Test & Measurement Solutions

TCP Open Connection and Error Code 1

So, I have a client that is supposed to continuously try to connect to a server using TCP Open Connection.vi. When the connection is established, the loop is supposed to exit.
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while (error)
attempt to open connection
Pretty simple, right?
I've had no issues with servers written in LabVIEW, but when attempting to integrate with a server that was written in C, it appeared that the client created multiple connections. I have been able to reproduce this problem by writing a server with Java. The C server was on a remote machine, the Java server on a local. Both see different numbers of additional connections (3 for C, 2 for Java).
Looking at the error codes, I am getting a bunch of code 56 (timeout, expected) and the ocassional code 1 (unexpected). I have noticed that whenever I have this multiple connection problem, I show an error code 1 right before the valid connection attempt and loop exit. Is there someway that a connection is being established (or partially established), but labVIEW is still returning an error? Is there a better way to verify that a TCP connection was actually successful?
Here is example output from the attached code, it shows the error codes generated
56
56
56
1
56
56
56
56
56
56
56
1
56
56
56
56
56
56
56
1
Here is output from my Java code
[2006-05-24 15:43:23.556] - Begin Listening for Connection Attempts
[2006-05-24 15:43:23.587] - Accepting Connection
[2006-05-24 15:43:23.603] - Begin Listening for Connection Attempts
[2006-05-24 15:43:23.603] - Accepting Connection
Running ServerNIOConnection Thread
[2006-05-24 15:43:23.603] - Begin Listening for Connection Attempts
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Thanks,
Martin
Message Edited by mmathis2000 on 05-24-2006 05:50 PM
Attachments:
Sample Client.vi ‏21 KB

Hello,
I’m a little curious why you are setting up your client like
this. If it is your objective to just
have the client wait until a connection is made, why not just have the TCP
connect VI have timeout value of ‘-1’ meaning “do not timeout”. This will allow the built-in TCP event
structure to listen for connections and ‘wake up’ your program when a
connection is established. I say this,
because the error messages seem to be dependant on the timeout values. For example, wire in 1ms to the timeout and
see how the messages differ in timeouts as opposed to wiring in “2000” for the
timeout value. This is because the
Connect VI attempts a connection and waits only the specified timeout before
abandoning that attempt and continuing with another attempt. I’m betting in your case connecting to the
server takes longer than your timeout value, so the connection is initiated by
your LV client, the handshaking takes place, your server indicates that a
connection is being made, and sometime during this process your timeout expires
and LV tries the process again thus you see the multiple connections. Go ahead and try this as an experiment – take
your VI, and instead of using ‘localhost’ use the IP address of your favorite
website and change the remote port to port 80.
Change the timeout to -1 and wait for the connection, then change the timeout
to 1 and see all the timeout errors given.
Hopefully this answers your question, please let me know if
you have any additional questions or if this is inaccurate/unclear.
Travis M
LabVIEW R&D
National Instruments

Tcp open connection problem while parallel tcp communication

I have a problem with TCP Open connection while running another TCP transfer.
While I run the Simple Data Client/Server example (..NI\LabVIEW 2010\examples\comm\TCP.llb) I would like to open another TCP connection according this simple VI attached. This runs on another port than the running Client/Server example. When the address of the PC to be connected to, is known to the network (IP/Name) all is fine, when the address is a name unknown to the network, than a significant delay in the datatransfer of the client/server example occures. Hope that anybody can reproduce/explain this behaviour.
Network setup here is Gigabit ethernet/ DHCP / Windows XP Prof. SP3/ LV 2010 / LV 8.6.1
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Attachments:
TCP_Open_blockingproblem.vi ‏16 KB

I really appreciate your comments,
to make sure that we do see the same effects let me exactly explain what I see: I open the example vi's : Data Client/Server example (..NI\LabVIEW 2010\examples\comm\TCP.llb. You can open it localy that means on one PC or open one on another PC. To make it simple for the first try open it localy and run both vi's according the example instructions. On the Data Client.vi I see now the samples updating many times per second (should be every 25 ms, because the server produces these in this intervall). All is like expected. Now open the TCP_Open_blockingproblem.vi from above and let it run unmodified (except you have an PC named 'DataServer0'). What I see now in the Data Client.vi : The samples update came nearly to an halt (this is why I called it 'blocking'). Updates only every 6 seconds (here in my network setup). Now stop the TCP_Open_blockingproblem.vi. The DataClient.vi is running on the same speed as before. Now modify the 'DataServer0' to a pc name existing in your network and start again. This time the sample speed is not degraded. Can you confirm this behaviour ?.
I did recognise the effect for the first time while I desigend an appliaction based on the STM library and posted the effects I saw, here : http://forums.ni.com/t5/Components/Simple-TCP-Messaging-STM/td-p/583438/page/5. Like Christian Loew supposed there is a bunch of code around. It is a multi tier application receiving TCP traffic on some ports and distributing on others. So I decided to isolate the problem from STM and my own code and came to the simplest code which I thought it was possible where the problem still occures which I described above.
Your suggestion to lookup the names once in the beginning of the application is a possible way, but I must say with the experience now I am still very uncertain of more unexpected future side effects during lookup, especially on network setups at customersites where I have no direct access. So I decided to give an UDP registration mechanism a try, like it is realised in the STM Examples of HostReceiver.vi and Target Sender.vi.
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Tcp data b/w labview and c++

Hi
i am trying to establish TCP connection b/w LABVIEW and C++ program. Server is established in C++ while client is implemented in labview.Although connection is successfully establish b/w server and client, both are unable to correctly understand data send/receive among them. Forexample if i want to send an int type send_array from server, i use standard WINSOCK function "send" like that:
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Kindly help me
Best Regards
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Go to Solution.

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How to use WAN IP with port number in TCP Open Connection ?

I have a code to write / read a WiFi device server that gets DIO / AI data through a serial port. See attachment.
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SRKIM: GL open period 시 hang이 발생할 경우

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Solution Description
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