Ptvs: Very slow loading after "Enable native code debugging"

[dilbert168]

I have following this post and get mix mode debug working.
VS version : Community 2017
Python version : 3.71
Running on Window-10

The loading time of the project become very slow (> 30 secs) after the "Enable native code debugging" feature is enabled.
I believe due to matplotlib & socket is imported in Python project.
As I use a sample project to start, it cut down to (10 secs), still longer than normal Python Debug start (1 sec).

As my most interest is debugging the C code, any method to improve loading time ?

[huguesv]

I don't know of any way of speeding up the mixed mode debugger (yes it is slow compared to the python debugger). Maybe @int19h as ideas?

Maybe start without debugging, then debug->attach would actually save you time, despite the manual steps?

[int19h]

This usually happens on importing of very large packages, mostly because the debugger is tracking the creation of code objects, and there are a lot of them (one per function).

The workaround is, indeed, to attach after imports are done.

A long-term fix would be to implement Just My Code in the mixed-mode debugger, so that imported modules aren't traced at all, and all internal breakpoints are disabled inside them.

[jaybo]

The suggestion to "attach after imports are done" doesn't seem to help. As soon as attach, I experience the same loading delay. FYI, we have a large python/C++ codebase and loading can take up to 3 minutes on a hot rod machine when "Enable native code debugging" is enabled. And for 99.9% of the modules loaded I don't need source level debugging. I'm curious why the "Symbols: Load only specified modules" radio button can't be used to limit the Python modules which can be used for source debugging.

[int19h]

Python modules don't actually have symbols, it's just a VS artifact. Since the actual slowdown comes from tracing code unnecessarily as it runs, JMC is the proper knob for such a feature. We just don't have anything like that implemented yet.

Can you tell a little bit more about what the experience looks like when you attach post-import? Is there anything else printed in debugger output window in addition to all the "Module loaded" notifications? e.g. exceptions?

[jaybo]

No exceptions were seen. The load process pauses momentarily for like a second or two on a couple of modules, but generally the load listing progresses pretty smoothly.

Here are the load timings for VS2017 Version 15.9.6:

Legacy Debugger:
Normal, Python only debugging: 3 seconds
Python / C++ debugging, Debug.StartDebugging:  4 minutes
Python only, then Debug.AttachToProcess: 100 seconds

NOT Legacy Debugger:
Normal, Python only debugging: 3 seconds
Python / C++ debugging, Debug.StartDebugging:  6 minutes
Python only, then Debug.AttachToProcess: 130 seconds

I've attached the output from Debug.AttachToProcess and Debug.StartDebugging.

AttachToProccess.txt
DebugRun.txt

[jaybo]

Oh, and of course the yellow banner at the top of the VS2017 screen is proclaiming:
"Debugger performance may be improved by loading fewer symbols"
which gives a false sense of hope.

[int19h]

Sorry for going dark on this for so long. And thank you for the logs and the numbers! Yeah, it sure looks like it's a general perf issue, because everything gets traced. We really do need JMC for mixed-mode.

@huguesv, you might want to make this one a tracking bug for it. Or create a new one - I think we had some perf bugs on MMD, but they were probably closed a long time ago.

[huguesv]

Thanks @int19h we did have another one, but we'll keep this one since it has the discussion.

[Joe459]

Any update on a fix for this? Just My Code for Mixed-Mode Debugging would be a lifesaver for me!

[Joe459]

I'm dying trying to work around this - I end up having to identify one of three python processes with changing PID's, on top of the manual attaching, making the mixed-mode debugging process particularly difficult/annoying. Any update on Just My Code? If not, how does one name a VS debugging process for identification and automatic attaching?