High CPU usage with documentSymbols code

[sean-mcmanus]

I noticed the fans were running on my MacBook, and I opened Activity Monitor to see that cpptools was using 98% CPU. I've had VS Code closed on my Mac since last night (when I opened approx 50 different cpp files), so I am not sure why cpptools would be running and using so much CPU right now.

Please let me know if there is a better place for me to report this bug, or if there are some logs I could collect and provide. I am running macOS Big Sur, and my C/C++ for VS Code is 1.2.2-insiders2.

Edit: I've also included photos of the stack trace, profiled using these instructions

Originally posted by Tyler Davis (@TylerADavis) in #6238 (comment)

[sean-mcmanus]

It looks like there's some code in the particular file that is causing our document symbol code to potentially infinite loop. If you can provide some sample code that would enable us to debug/fix the issue.

[TylerADavis]

Hi Sean, thanks for opening this. This may be a bit of an edge case, as this happened after grading 50 student assignments for coding style. I've included the full issue template below, please let me know if there is anything else that would be useful. Note that I only noticed high CPU ~12 hours after closing VS Code. I've run into this issue at least once before, but I don't recall if that was also after grading. My last google search for cpptools was the day after my last batch of grading though, so it's possibly related.

Type: LanguageService

Describe the bug

• OS and Version: macOS Big Sur
• VS Code Version: 11.2.1
• C/C++ Extension Version: 1.2.2-insiders2
• Other extensions you installed (and if the issue persists after disabling them):
• Does this issue involve using SSH remote to run the extension on a remote machine?: No
• A clear and concise description of what the bug is, including information about the workspace (i.e. is the workspace a single project or multiple projects, size of the project, etc).: I noticed the fans were running on my MacBook, and I opened Activity Monitor to see that cpptools was using 98% CPU. I've had VS Code closed on my Mac since last night (when I opened approx 50 different cpp files), so I am not sure why cpptools would be running and using so much CPU right now.

Steps to reproduce

This is at least the second time I've encountered this issue, but I don't yet have exact repro steps.

1. Open 50 separate .cpp files, each in their own folder, then quit VS Code. This weird workflow was from grading CS projects.
2. Come back the next morning
3. Use computer normally for ~1hr
4. Notice fans are spinning up on laptop, open activity monitor, observe high CPU usage of cpptools

Expected behavior

I expect cpptools to not use high amounts of CPU while VS code is closed, especially if it has been closed for 12 hrs.

Logs

# Logs from C/C++ Log Diagnostics
-------- Diagnostics - 2/22/2021, 11:49:28 AM
Version: 1.2.2-insiders2
Current Configuration:
{
    "name": "Mac",
    "includePath": [
        "${workspaceFolder}/**"
    ],
    "defines": [],
    "macFrameworkPath": [],
    "compilerPath": "/usr/local/bin/g++",
    "cStandard": "gnu11",
    "cppStandard": "gnu++98",
    "intelliSenseMode": "macos-gcc-x64",
    "compilerArgs": [],
    "intelliSenseModeIsExplicit": true,
    "cStandardIsExplicit": true,
    "cppStandardIsExplicit": true,
    "compilerPathIsExplicit": true,
    "browse": {
        "path": [
            "${workspaceFolder}/**"
        ],
        "limitSymbolsToIncludedHeaders": true
    }
}
No active translation units.

# Output from language server logging

File exclude: **/.git
File exclude: **/.svn
File exclude: **/.hg
File exclude: **/CVS
File exclude: **/.DS_Store
File exclude: **/.vscode
Search exclude: **/node_modules
Search exclude: **/bower_components
Search exclude: **/*.code-search
Search exclude: **/.vscode
Populate include completion cache.
Discovering files...
  Processing folder (recursive): /Library/Frameworks/digitizer.framework/Versions/2.4.0/Headers/
  Processing folder (recursive): /Library/Frameworks/conveyor.framework/Versions/2.4.1/Headers/
  Processing folder (recursive): /Library/Frameworks/jsonrpc.framework/Versions/2.4.0/Headers/
  Processing folder (recursive): /Library/Frameworks/thing.framework/Versions/2.4.0/Headers/
  Processing folder (recursive): /Library/Frameworks/mbqtutils.framework/Versions/2.4.0/Headers/
  Processing folder (recursive): /Library/Frameworks/mbcoreutils.framework/Versions/2.4.0/Headers/
  Processing folder (recursive): /Library/Frameworks/R.framework/Versions/3.3/Resources/include/
  Processing folder (recursive): /Library/Frameworks/conveyor-ui.framework/Versions/2.4.0/Headers/
  Processing folder (recursive): /Library/Frameworks/Python.framework/Versions/2.7/include/python2.7/
  Processing folder (recursive): /Library/Frameworks/toolpathviz.framework/Versions/2.4.0/Headers/
  Processing folder (recursive): /Library/Frameworks/Eigen.framework/Versions/2.4.0/Headers/
  Processing folder (recursive): /Library/Frameworks/IntelPowerGadget.framework/Versions/A/Headers/
  Processing folder (recursive): /Library/Frameworks/jsoncpp.framework/Versions/2.4.0/Headers/
  Processing folder (recursive): /usr/local/include/
Checking for syntax errors: file:///Users/tylerdavis/Documents/Grad%20School/Fourth%20Year/Winter%20Quarter/CS%2031/Grading/Project%204/Done/Project%204/array.cpp
sending compilation args for /Users/tylerdavis/Documents/Grad School/Fourth Year/Winter Quarter/CS 31/Grading/Project 4/Done/Project 4/array.cpp
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  other: --g++
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  Processing folder (recursive): /usr/local/lib/gcc/x86_64-apple-darwin15.0.0/5.2.0/include/
  Processing folder (recursive): /usr/local/lib/gcc/x86_64-apple-darwin15.0.0/5.2.0/include-fixed/
  Discovering files: 25776 file(s) processed
  0 file(s) removed from database
Done discovering files.
Parsing remaining files...
  Parsing: 0 files(s) processed
Done parsing remaining files.
Queueing IntelliSense update for files in translation unit of: /Users/tylerdavis/Documents/Grad School/Fourth Year/Winter Quarter/CS 31/Grading/Project 4/Done/Project 4/array.cpp
Error squiggle count: 10
Error squiggles will be disabled in: file:///Users/tylerdavis/Documents/Grad%20School/Fourth%20Year/Winter%20Quarter/CS%2031/Grading/Project%204/Done/Project%204/array.cpp
Update IntelliSense time (sec): 9.526
idle loop: reparsing the active document
Checking for syntax errors: file:///Users/tylerdavis/Documents/Grad%20School/Fourth%20Year/Winter%20Quarter/CS%2031/Grading/Project%204/Done/Project%204/array.cpp
Queueing IntelliSense update for files in translation unit of: /Users/tylerdavis/Documents/Grad School/Fourth Year/Winter Quarter/CS 31/Grading/Project 4/Done/Project 4/array.cpp
Error squiggle count: 10
Update IntelliSense time (sec): 0.26
idle loop: reparsing the active document
Checking for syntax errors: file:///Users/tylerdavis/Documents/Grad%20School/Fourth%20Year/Winter%20Quarter/CS%2031/Grading/Project%204/Done/Project%204/array.cpp
Queueing IntelliSense update for files in translation unit of: /Users/tylerdavis/Documents/Grad School/Fourth Year/Winter Quarter/CS 31/Grading/Project 4/Done/Project 4/array.cpp
Error squiggle count: 10
Update IntelliSense time (sec): 0.263

Screenshots

Additional context

[TylerADavis]

As for a code snippet, since this was after grading ~50 student assignments, I'm not sure if this is perhaps due to one particular .cpp file that was submitted, or if it is perhaps due to rapidly opening many copies of identically named cpp files that all contain identically named functions.

I've included an image below showing the general layout of the files at the time I opened them. Would it still be helpful to see a code sample to get an idea of how the submissions look?

[sean-mcmanus]

The issue is most likely triggered by code in a particular file and not by rapidly opening many different files. Are you able to locate the file that is triggering the issue? You would likely see the Outline view fail to be populated. If you set C_Cpp.loggingLevel to "Debug", then the C/C++ output pane should show something like
cpptools/getDocumentSymbols: <file> and the last message would most likely show which file is causing the issue.

[sean-mcmanus]

The code that exists at a non-local scope is the most likely to be the cause, so function definitions/bodies are unlikely to be needed for the repro.

[TylerADavis]

Here is a gist containing the debug logs: https://gist.github.com/TylerADavis/b62ec12b45bf0ee7dad652a4b61509a1

The debug logs appear to be specific to the file I have open at the moment I open the output pane, is there a way to get logs for all open files / just get logs from the instance of cpptools that is stuck in a loop? Or would I need to manually open each submission and see which one is hanging / not populating the outline view?

[sean-mcmanus]

There should be one cpptools process per VS Code instance...assuming you're not seeing a dangling one from a previous instance then most likely the cpptools process belongs to the VS Code instance that is currently open. You should be able to close the VS Code instance and reopen that same file to retrigger the repro, right?

I found a repro of an infinite loop using

namespace foo::foo::foo::foo
{
	int i;
}

which I reported at #7025, but I'm guessing your repro is probably different and I'm not sure yet if they share the same root cause.

[TylerADavis]

Ah, this looping one must be dangling from a previous VS Code instance then. I hadn't realized that cpptools is supposed to shut down with VS Code, and activity monitor does show two instances of cpptools. I'll reopen all files and see if that can get the properly behaving cpptools currently idle at 0% CPU to get stuck at 100%.

[TylerADavis]

I've reopened all the files I could think of that might have triggered this loop, but I didn't have any success getting another cpptools process looping. Do you have any other recommendations for how I might find out what got the looping process (I still haven't killed it) stuck? Also, is it possible that deleting a file from disk while analysis is incomplete could cause this issue? I also wonder if it is necessary to quit VS Code or wait a certain time period in order to trigger this bug (I'm not too familiar with how cpptools and the language server are architected, so I'm not sure what's reasonable). I'm assuming there is a way to consistently repro this, but it seems simply opening the files isn't sufficient (assuming one of the student submissions was the culprit).

Workflow while grading:

• Unzip folder
• Open cpp file in VS code
• Scroll through file
• Occasionally accidentally type grading comments into the cpp files directly, e.g. #include <string>-1 some functions lacking documentation
• Unzip another folder
• Occasionally close VS Code windows to remove unneeded tabs
• Occasionally delete unzipped assignments from disk (both .cpp file and enclosing folder)
• Finish grading
• Close VS Code
• Notice high CPU usage and ~10 hrs of CPU time on cpptools the next morning

Flow when attempting to reproduce:

cd project4/Tyler # Same flow for project3
# Unzip all project files in Finder
# Open all cpp files in VS code
code ./*/*.cpp

At this point a VS code window opens with ~50 tabs. I look at each tab one by one, waiting until the outline view populates and the files are scanned for errors. I observe that all outline views successfully populate, and all files are scanned for errors.

This image shows the stuck cpptools from last night, as well as two new cpptoolsprocesses. I believe these two cpptools processes correspond to the two open VS Code windows I have.