RTD updatevalue on worker thread

[Ashutosh Bhardwaj]

Hi, 

I have a question about RTD threading.

So, let's say I have a RTD server that starts like below on main thread 

 public class DemoRtdServer : ExcelRtdServer
 {
     protected override bool ServerStart()
     {

Now, I update the value on a worker thread (timer, non-blocking collection etc)  like, 
topic.UpdateValue(objValue);

Is there something inbuilt under the hood that will ensure/ synchronize that the update only happens on main thread or the thread that started the server? 

Or do I need to manually synchronize? 

Many Thanks,
Ashutosh

[Govert van Drimmelen]

Yes, the ExcelRtdServer base class in Excel-DNA implements a mechanism that ensures cross-thread UpdateValue calls are safe and reliable. The implementation is quite complicated and has evolved over time, but I know of no current problems.

-Govert

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[Ashutosh Bhardwaj]

Hi Govert, 

Thaks for the reply. I recently started to run into a new bug where, rtd is randomly returning ExcelEmpty. 

1. I store the results in a Dictionary<string, objec[,]> , here the key is GUID.ToString()
2. Then update the value with topic.UpdateValue(key) which is guid string. 
3. Check that its a valid non-empty guid string, right before calling updatevalue. Its always a   non-empty guid string. 
4. But, object result= XlCall.RTD  returns ExcelEmpty.

happens intermittently. 

Any suggestions? 


Thanks,
Ashutosh

[Govert van Drimmelen]

I'm not sure I understand the interaction between the UpdateValue calls and the dictionary you keep.

The callback from Excel that runs the wrapper UDF does not happen synchronously with the UpdateValue call (and runs on the main thread, which might not be the one calling UpdateValue).

It does not sound like something that is a bug in the ExcelRtdServer mechanism, though that code and the interaction with Excel is complicated, so might be going wrong.

It would be useful to try to make a small project that reproduces the issue.

-Govert