Multi-Threading, Visual Studio, and Breakpoints.

[Alex Sokolek]

This is a repost, now that ChatGPT is working again...

Hi. I need some clarification and/or help with a multi-threaded application being debugged with Visual Studio.

I notice that when I hit a breakpoint in a thread, it stops, and I can examine the status and values, but when I step to the next instruction, the debugger goes back to the original breakpoint. I think I understand that a different thread is hitting the breakpoint, and that when one thread is stopped, they all seem to stop, until I go forward. Is this understanding correct?

Is there a way to hold the other threads, while I single step the first one? Also, is there anything in the debugger that will identify the particular thread that is stopped at the breakpoint? If it matters, I have Visual Studio 2022 Community, Version 17.9.6, and I am debugging a C++ program. Thanks.

 

[ChatGPT]

Hello,

Yes, your understanding of how breakpoints work in a multithreaded program in Visual Studio is correct. The behavior you're seeing is because execution is being halted due to a different thread hitting the breakpoint after you try to step over.

Here are the responses to your queries:

1. As for holding other threads while single stepping one, Visual Studio only freezes the thread that triggers the breakpoint by default. This is to avoid losing synchronization between threads. However, you can freeze and thaw individual threads manually:

- To do this, during debugging, open the Threads window (Debug > Windows > Threads).
- This window shows you the list of all the currently running threads. You can right-click on a thread and select 'Freeze' to stop it from executing any further code. To allow it to resume execution, you can right-click on it again and select 'Thaw'.

Remember that manually freezing and thawing threads can lead to unexpected results if your application is heavily dependent on thread synchronization.

2. The debugger in Visual Studio does indeed provide information about which thread has hit the breakpoint. You can view this in the Threads window (Debug > Windows > Threads):

- The current thread (the one that has hit the breakpoint) is highlighted in yellow. You can also see detailed thread information in the 'Details' section of this window.

As you're using Visual Studio 2022 Community, you should have access to these features. Every time you hit a breakpoint, you can check the Threads window to see which thread has been stopped and manage the execution of other threads as necessary.

Hopefully, this should help you with your multi-threaded debugging in Visual Studio. Let me know if you need any further clarification!

 

[Alex Sokolek]

Thank you. That helps.