Visual Basic/VB, Calling code in DLL that has an "infinite Loop"

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Visual Basic/VB >> Calling code in DLL that has an "infinite Loop"

by Mike Larson » Sat, 13 Sep 2003 03:41:29 GMT

Hello,

I'm trying to tie some hardware my company builds into a PC. I'm running
Win98 on the PC and can access my hardware C++ functions in a DLL. Right
now I'm checking if the hardware puts up some information then when the PC
gets around to it, it reads the informaiton. This is leading to a lag in
data because the PC can get busy with other things and not read the data
right away.

I'm wondering if there is a way to start a routine in the C++ dll that uses
a near infinite loop to "interrupt" the vb6 program when data comes in by
putting the data into something like text box.

I am not creating driver DLL yet, just a C++ program compiled into a DLL.

Can this be done? Would someone have some advice on accomplishing this?

Thanks.

Mike



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Visual Basic/VB >> Calling code in DLL that has an "infinite Loop"

by Stephen J Whiteley » Sat, 13 Sep 2003 04:28:42 GMT

How much of a 'lag' are you talking about?

if your hardware just 'dumps' data into a specific location (your DLL) you
could have your program poll the DLL for new information, say, every 10mS
(or 50 or 100, or whatever).
(i'm presuming this is pretty close to what you've got). If the data comes
in fast, and you can tolerate a few mS lag, but want to get ALL the data,
put the data (in the C++ DLL) into a circular buffer, and when the VB app
gets round to checking for data, it can read the data as a block.

Unless you are doing real-time control, I can't imagine a problem with even
a huge delay of 500mS - which is plenty of time for a VB app to do pretty
much anything with a huge chunk of data.

If you want it 'event driven' then you will have to make a COM DLL that can
create events that your VB app will receive.

BTW, if you are serious about doing this sort of thing, go with NT/2000/XP,
and drop 98.

Stephen J Whiteley



uses



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Visual Basic/VB >> Calling code in DLL that has an "infinite Loop"

by Stephen J Whiteley » Sat, 13 Sep 2003 06:40:50 GMT

ave your C program actually go into an 'infinate loop'! Add a Sleep()
command in the loop, and a 'getout' clause so you can end it. (sounds like
your familiar with C, so you may be able to achieve this, but it all depends
on how you are using/creating the DLL and getting it to run).


you could then have your C DLL create a shared memory region where it can
put flags/data, and have your VB program grab the data out of shared memory
on a fixed interval (20mS, say), then you are assured (as assured as anyone
can be) of a maximum lag of 20mS. This really depends on what you are
monitoring.

Alternatively, why can your VB program not access the very same APIs your C
program does? This may be easier, depending on the APIs. Then you can do
your polling in VB.

You can go the route that you yourself suggested, but you somehow have to
get the text into the text box, and trigger the change event...could be
messy, However, you could send a windows message to your VB application
using the SendMessage (or PostMessage) API. Does that sound feasable to you?
It'll require the VB application window being subclassed, so you can get
access to those messages.

Driver development is not an area you want to delve into lightly (can't be
done from VB), and not something you can knock out in a day.

Hope (some) of this gives you a better idea.

SJW


"Mike Larson" < XXXX@XXXXX.COM > wrote in message
news: XXXX@XXXXX.COM ...
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Visual Basic/VB >> Calling code in DLL that has an "infinite Loop"

by btpanek09 » Sat, 13 Sep 2003 23:06:37 GMT

ou could create a Thread in the DLL that would be your "endless loop"
to monitor the event. Then when the event occurs as detected by the
Thread in the DLL you could use a CallBack function to notify the VB
program from the DLL. I have used the CreateThread inside a DLL to
create a separate process that can monitor an event like a Serial port
and Socket reads.

The Thread has the advantage of not being bound to the VB process.
The VB program is not tied directly to the loop inside the Thread and
will then not lock up waiting for the loop to finsih.

I have gotten the CallBack function to work using sample-code provided
for EnumWindows from MS, however I haven't gotten it to work in a
situation like you have mentioned. But, it should be possible.



"Stephen J Whiteley" <yakATsteelcoder.com> wrote in message news:< XXXX@XXXXX.COM >...

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Visual Basic/VB >> Calling code in DLL that has an "infinite Loop"

by Mike Larson » Mon, 15 Sep 2003 22:32:51 GMT

entlemen,

Thank you for your responses. I think I get the idea but I would like to
run my idea here and get some feedback as to what I can expect

The code goes like this :

DWORD WINAPI ThreadProc(LPVOID lpParameter)
{
HWND TheControl
lpString AString [40]; //Null Terminated String

TheControl= lpParameter;
while (near infinite loop) {
//my code
SetWindowText(TheControl, AString; );
SendMessage(TheControl, WM_KEYUP, 0, 0);
}
}

int _stdcall StartTheThread (HWND TheControl) ) {
{
//This routined called from VB App


HANDLE hWorkerThread;
DWORD dwThreadId;

hWorkerThread = CreateThread (NULL,
0,
ThreadProc
TheControl,
0,
&dwThreadId);

I will call StartTheThread from my VB app with the handle to a text box and
start the near infinite loop. When my near infinite loop is ready to
tranfer info it will call the SetWindowText and the SendMeassage call which
will cause at leaset the KeyUp event in the text box and possibly the Change
event.

Now I've read that using the plaine CreateThread may cause some problems if
calling other run time libraries. Am I in this case? Should I use
"_beginthreadex" or AfxBeginThread?

Thanks for the help.

Mike



"Brad Panek" < XXXX@XXXXX.COM > wrote in message
news: XXXX@XXXXX.COM ...
news:< XXXX@XXXXX.COM >...
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