Debugging dll sometimes cause load symbol problem

PLECS
1

I have a model A that has another model B as a sub-module. I have kept a DLL block inside submodule B and linked it to correct dll file. Through visual studio I want to debug while simulation. So I use attach process feature to attach it to plecs.exe with the name showing the model A. Everything usually goes well.

But sometimes I see this error:

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Once this error starts popping up, no matter what I try, it never solves. I have to revert back all the changes I did in plecs and restart laptop and freshly start again it works.

So any of you have idea what happen here?

2

Hi Vishwesh,

Visual Studio official documentation provides guidance on this topic. There is quite a bit of other guidance regarding this error across stack overflow and other programming sites as it often relates to the build process, loading the wrong dll, caching of symbols, etc.

A few other thoughts related to PLECS integration:

  • If PLECS has crashed, use your task manager to ensure no plecs.exe instances are lingering. Windows will not unload a DLL while the process lives and VS will silently keep stale symbols. You want to ensure you’re connecting to the correct plecs.exe instance.
  • Best practice would be to attach the debugger before running the model in PLECS.
  • If the same DLL is loaded multiple times in one simulation or even multiple different simulations one needs to be cautious.

Regards,
Bryan

3

Hi Bryan,
Thanks for your response. I followed the VS documentation and loaded the suggested symbols PDB file. However, even after selecting the correct PDB file, I still get the message: “could not load the symbol.”
For context, PLECS had crashed earlier, and I restarted it before this issue occurred. At the time of the crash, I made sure to open Task Manager and manually end the lingering plecs.exe process.
I’d like to clarify the best practice here. Do you mean the recommended sequence is:

  1. Load the model in PLECS
  2. Attach VS to the PLECS model’s executable (the one titled myModelName in my example image)
  3. Run the model simulation

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4

Yes, that is the recommended sequence. Once PLECS crashes, the operating system and VS Code are responsible for managing the DLL resources.

After the crash have you tried:

  • Clean Solution → Rebuild (in Debug mode) ensuring that DLL is fully deleted
  • Tools → Options → Debugging → Symbols and click Empty Symbol Cache
  • Performing the above steps and restarting Visual Studio?

Of course one needs to ask - why is PLECS crashing? With a DLL block it’s typical that the crash is a result of actions within the DLL. Presumably you are using breakpoints for this purpose, but one could always default back to clunkier print debugs, and then revert back to a more typical workflow.

5

Past week I tried with recommended sequence, ie. always attach to process first and start simulation. This really helped. I didn’t face any issue for a week now.

Regarding cacheClear suggestion, I’ll try once it crashes again and update here.

Thanks

6

Glad to hear that makes an improvement. Thanks for the update!