C++ Just My Code Stepping in Visual Studio(blogs.msdn.microsoft.com)

131 pointsby jjuhl8 tahun yang lalu38 comments

blogs.msdn.microsoft.com

C++ Just My Code Stepping in Visual Studio

https://blogs.msdn.microsoft.com/vcblog/2018/06/29/announcing-jmc-stepping-in-visual-studio/

41 comments

Great. Now if they can actually fix the debugger to lock onto a single thread when stepping thru multithreaded code. Currently when you set a breakpoint and step, you’ll be jarringly switched back to the breakpoint when another thread hits it. The solutions now are tedious : https://visualstudio.uservoice.com/forums/121579-visual-stud...

1_player8 tahun yang lalu

The problem is that the normal implementation of a breakpoint/step is replace a single byte with a 0xCC opcode (INT 3), which will be hit by every thread. Making it lock onto a single thread would require a conditional breakpoint, checking the thread ID every time that code path is executed, which might potentially use a lot of CPU. I'm not sure that kind of conditional breakpoint has hardware support.

It's definitely possible to implement, but not as easy as using a regular INT 3 instruction.

nitwit0058 tahun yang lalu

Not sure anyone would care about that cost. Generally people are glad to waste CPU time instead of human time.

legulere8 tahun yang lalu

Should be doable with help from the operating system to have thread-local storage for the code segment when debugging.

1_player8 tahun yang lalu

That sounds like a pretty good idea, would be nice to see gdb implement something like that.

neverfone8 tahun yang lalu

Not a windows user, but the same applies to gdb. What is your proposal? If you're currently debugging a thread, breakpoints are disabled for other threads? That really doesn't seem like what people would expect by default.

phendrenad28 tahun yang lalu

It’s a UX issue, not a behavior issue, I think. What I would do is... after the user presses the “step” button, until the user presses the “continue normally” (or whatever the free run button that ends the debugger is in VS), if breakpoints are encountered in other threads, they are quietly opened in new tabs, places under the current debugger tab. Maybe flash the tab a bit to let the user know this has happened. I don’t think VS has tabs for the debugger interface, so it would need that added.

neverfone8 tahun yang lalu

Hmmph, I see what you're saying, that sounds like it could work.

I think the tab flashing is the critical detail, otherwise you would be confused why things are deadlocking.

jamesfmilne8 tahun yang lalu

GDB can do that already.

   (gdb) help set scheduler-locking 
   Set mode for locking scheduler during execution.
   off  == no locking (threads may preempt at any time)
   on   == full locking (no thread except the current thread may run)
   step == scheduler locked during every single-step operation.
      In this mode, no other thread may run during a step command.
      Other threads may run while stepping over a function call ('next').

Arnavion8 tahun yang lalu

The VS debugger can freeze threads too. Neither gdb nor VS can help AFAIK if the user doesn't want to freeze the other threads.

giancarlostoro8 tahun yang lalu

GDB has all sorts of super powers but is there a GUI that works well with GDB?

renox8 tahun yang lalu

Yes, gdb --tui ;-)

maxxxxx8 tahun yang lalu

Agreed. That's a real nuisance.

melling8 tahun yang lalu

Someone had a useful gdb trick in a previous post:

https://news.ycombinator.com/item?id=17427001

“”” with gdb 7.12 or later, you can exclude files matching a glob with "skip -gfile", e.g. "skip -gfile /usr/*" “””

_slyo8 tahun yang lalu

Using libClang and gdb: http://jefftrull.github.io/c++/gdb/python/libclang/llvm/2018...

a-dub8 tahun yang lalu

It would be pretty funny if they extended it to "just my uncommitted changes." ie: I want to step through every line I have written, but skip everything else...

scraft8 tahun yang lalu

It is funny how long this has been an issue and how I and so many people have given up stepping in and instead jump to the actual user function, set break point, and then step over at the source location, then unset the breakpoint and continue. A bunch of crazy steps which you end up doing again and again.

Needless to say, this improvement is much welcomed!

Dinux8 tahun yang lalu

Visual Studio even created the "Jump to here" option to do just this, but I agree this is how we all did it for a long time.

[deleted]8 tahun yang lalu

Dinux8 tahun yang lalu

As a developer spending hours a day in Visual Studio with C++ as primary language this is a major improvement in terms of development time. Debugging is a a time consuming task in any language, but library headers from STD and Boost slow down the process tremendously.

johnboyer8 tahun yang lalu

Although it does help, I would say its only a bit faster than actually just setting a breakpoint of where you want the code to stop, and running till then, unlike Microsoft's example which shows 85 step intos, as if people actually do that.

hhmc8 tahun yang lalu

It depends on the purpose of your debugging. If you know exactly where you want to go then, as you say, this has diminished value. but debugging can often be exploratory, in which case this feature could be a real timesaver.

Dinux8 tahun yang lalu

We, for example, have lots of classes and structures that are designed to the interfaces provided by the STD containers. Mix that with actual STD containers and you can spend several hours trying to find the problem. Just My Code eliminates much of that since almost always the STD is not the cause for the problem.

spoiler8 tahun yang lalu

I love this idea. I wonder if something similar could be ported/achieved for JavaScript!

maddyboo8 tahun yang lalu

Not exactly the same, but you can use blackboxing [1] in the Chrome DevTools to isolate code you’ve written from library/framework code in the debugger.

[1]: https://developer.chrome.com/devtools/docs/blackboxing

spoiler8 tahun yang lalu

Thanks for this! I didn't realise this feature existed.

dmethvin8 tahun yang lalu

The Microsoft Edge browser has had this feature for two or three years, by the same name. Chrome has something similar.

https://docs.microsoft.com/en-us/microsoft-edge/devtools-gui...

brian_herman8 tahun yang lalu

I was thinking the same thing!

chris_wot8 tahun yang lalu

I would love to know the best Linux/OS X GUI debugger... and can it do this?

neverfone8 tahun yang lalu

I don't know if there are any good Linux GUI debuggers, but gdb is a comprehensive debugger and can do something similar with the skip command.

Any gui debugger for Linux is probably a frontend to gdb, so as long as it lets you passthrough commands to gdb it can do this.

pjmlp8 tahun yang lalu

I think DDD is still one of the best ones around given the display of data structures, even if the UI could get a facelift.

TylerGlaiel8 tahun yang lalu

Why does this require a special compiler switch? Can't the IDE just auto-step until it gets back to your own file of code?

[deleted]8 tahun yang lalu

w_t_payne8 tahun yang lalu

Why has it taken this long for something so obvious to be implemented?

Tempest19818 tahun yang lalu

With VS2017, they've moved to a faster release cadence. Fortunely, the minor releases are actually delivering significant features, like C++17 conformance.

The downside is occasional toolset compatibility issues. https://blogs.msdn.microsoft.com/vcblog/2017/11/15/side-by-s...

merinowool8 tahun yang lalu

So that people with VS2015 would have to buy new version...

rootlocus8 tahun yang lalu

I know you're sarcastic, but this was common practice at my previous shop.

Kenji8 tahun yang lalu

anilgulecha8 tahun yang lalu

Just a clarifying note : this is the closed Visual Studio, and not free software - VS Code - which usually does the rounds on HN.

I'm far more excited about the LSP protocol for C++ which would bring like this to all IDEs.

Rusky8 tahun yang lalu

I don't think the LSP includes any debugging support?

anilgulecha8 tahun yang lalu

I meant the sister/offshoot of LSP:

https://github.com/Microsoft/vscode-debugadapter-node/tree/m...

https://code.visualstudio.com/docs/extensionAPI/api-debuggin...