Debugging node app pauses unexpectedly when a Worker is created

[hogpilot]

Issue Type: Bug

After updating my VS Code, my debugging experience became unpredictable and would pause unexpectedly. I've traced down the root cause in my code to an instantiation of a node Worker (from the worker_threads module).

I have created a simple reproducible scenario with instructions here.

The problem manifests when a worker is created with an env option that doesn't include NODE_OPTIONS in the environment variable. (NOTE: I wanted the worker thread to act as a sort of "safe" sandbox, with no knoweldge of the owning thread's environment settings):

  import { Worker } from 'worker_threads';

  // This line will cause an unexpected pause in the "Worker1" call stack 
  const worker = new Worker(new URL('./worker.js', import.meta.url), { env: {} } );

  // This line will not cause an unexpected pause in the call stack
  const worker = new Worker(new URL('./worker.js', import.meta.url), { env: {NODE_OPTIONS: process.env.NODE_OPTIONS} } );

Steps to Reproduce:

1. Clone this repo: https://github.com/hogpilot/vscode-debug-test
2. Open the repo in VS Code
3. Run the following commands in the terminal:

npm install
npm run build

3. From VS Code's "Run and Debug" tab, select "Launch Program" (from my launch.json)
4. The code will pause in the Worker1 stack (without any breakpoints set) when it creates the new Worker

Workaround:

1. When creating the new Worker with an env option, add NODE_OPTIONS to the env object.

NOTE: I am using webpack5 to build the code, following their guidance for instantiating worker threads

• Node version: v14.16.1
• Webpack version: 5.38.1

VS Code version: Code 1.56.2 (054a929, 2021-05-12T17:13:13.157Z)
OS version: Windows_NT x64 10.0.17763

System Info

Item	Value
CPUs	Intel(R) Core(TM) i7-9850H CPU @ 2.60GHz (12 x 2592)
GPU Status	2d_canvas: enabled gpu_compositing: enabled multiple_raster_threads: enabled_on oop_rasterization: enabled opengl: enabled_on rasterization: enabled skia_renderer: enabled_on video_decode: enabled vulkan: disabled_off webgl: enabled webgl2: enabled
Load (avg)	undefined
Memory (System)	31.73GB (11.64GB free)
Process Argv	--crash-reporter-id f3ef9d22-974e-4c16-bdee-33c2342fccfa
Screen Reader	no
VM	0%

Extensions (6)

Extension	Author (truncated)	Version
vscode-eslint	dba	2.1.20
xml	Dot	2.5.1
vscode-env	Iro	0.1.0
mdx	sil	0.1.0
code-eol	soh	0.3.3
code-spell-checker	str	1.10.2

A/B Experiments

vsliv368:30146709
vsreu685:30147344
python383cf:30185419
pythonvspyt602:30300191
vspor879:30202332
vspor708:30202333
vspor363:30204092
vswsl492:30256859
pythonvspyt639:30300192
pythontb:30283811
pythonvspyt551:30311712
vspre833cf:30267465
pythonptprofiler:30281270
vshan820:30294714
vscoreces:30290705
pythondataviewer:30285071
vscus158cf:30286554
vscgsv2ct:30307505
vscorehov:30309549
bridgeflight:30312182
vscod805cf:30301675

[vscodebot]

(Experimental duplicate detection)
Thanks for submitting this issue. Please also check if it is already covered by an existing one, like:

• Node.js Debugger: Worker Threads names (#121196)
• VS code debugger keeps pausing on start (#122170)

[connor4312]

This appears to be an issue in Node.js, I've reported it here: nodejs/node#38934

We could patch around it in js-debug, PR's welcome. Code pointer: https://github.com/microsoft/vscode-js-debug/blob/3a3436a299113045c69fe8e07bb1b70b6ecde950/src/adapter/threads.ts#L626

[Patil2099]

I would love to help in solving this issue @connor4312. Can you guide me a little?

[bl-ue]

@Patil2099 take a look at nodejs/node#38934 — maybe you could do some investigation there as to why it's behaving that way :)

[connor4312]

Yea, you could patch Node (I'm not familiar with their internals enough to give pointers) or, inside _onPaused in js-debug, call this.resume() if we identify a paused worker. It looks like the event reason is "Break on start" in that case. You could make the type() in the NodeWorkerTarget something like node_worker, and then be able to identify in _onPaused that if the target is a node_worker and reason is break on start, then we should actually resume.