fix: process leaks in extensionHostConnection

[SimonSiefke]

Fixes #211462.

Details

When the connection closes, the extension host sends a disconnect message, and then closes the socket. The remote agent host, receives the disconnect message, starts its graceful cleanup but then the socket close event comes which immediately triggers extHostSocket.destroy() before the graceful cleanup is finished

Change

The change tries to ensure the extHostSocket gets shutdown gracefully, so that the cleanup code and still run and finish.

Test out locally (Linux)

1. Ensure vscode repo is set up in this branch using node version from nvmrc and run npm ci
2. Run npm run core-ci
3. Add product.overrides.json

{
	"nameShort": "Code",
	"nameLong": "Visual Studio Code",
	"applicationName": "code",
	"extensionsGallery": {
		"nlsBaseUrl": "https://www.vscode-unpkg.net/_lp/",
		"serviceUrl": "https://marketplace.visualstudio.com/_apis/public/gallery",
		"itemUrl": "https://marketplace.visualstudio.com/items",
		"publisherUrl": "https://marketplace.visualstudio.com/publishers",
		"resourceUrlTemplate": "https://{publisher}.vscode-unpkg.net/{publisher}/{name}/{version}/{path}",
		"extensionUrlTemplate": "https://www.vscode-unpkg.net/_gallery/{publisher}/{name}/latest",
		"controlUrl": "https://main.vscode-cdn.net/extensions/marketplace.json",
		"mcpUrl": "https://main.vscode-cdn.net/mcp/servers.json",
		"accessSKUs": [
			"copilot_enterprise_seat",
			"copilot_enterprise_seat_quota",
			"copilot_enterprise_seat_multi_quota",
			"copilot_enterprise_seat_assignment",
			"copilot_enterprise_seat_assignment_quota",
			"copilot_enterprise_seat_assignment_multi_quota",
			"copilot_enterprise_trial_seat",
			"copilot_enterprise_trial_seat_quota",
			"copilot_for_business_seat",
			"copilot_for_business_seat_quota",
			"copilot_for_business_seat_multi_quota",
			"copilot_for_business_seat_assignment",
			"copilot_for_business_seat_assignment_quota",
			"copilot_for_business_seat_assignment_multi_quota",
			"copilot_for_business_trial_seat",
			"copilot_for_business_trial_seat_quota"
		]
	}
}

3. Ensure sshd is installed ( sudo apt-get install openssh-server)
4. Add ssh config for starting local ssh server
5. Start ssh server
6. Launch VScode using ./scripts/code.sh
7. Install remote ssh extension
8. Open a new VSCode window
9. Open Quickpick and run Remote-SSH: Connect Current Window to Host
10. Enter the launched ssh server address
11. Wait for successful connection
12. Close the second VSCode window now
13. Use Resources App to check for still running processes
14. Repeat steps 8-13 a few times.

If there are leaks, the number of processes increases each time as described in the issue

Kooha-2026-06-01-12-05-37.mp4

Before

When opening a new window and connecting it to SSH and then closing it 3 times, the number of processes seems to increase each time:

{
  "processCount": {
    "after": 22,
    "before": 10
  },
  "isLeak": true
}

After

When opening a new window and connecting it to SSH and then closing it 3 times, the number of processes seems to stay constant:

{
  "processCount": {
    "after": 13,
    "before": 13
  },
  "isLeak": false
}

[Copilot]

Pull request overview

Note

Copilot was unable to run its full agentic suite in this review.

Updates extension host socket disposal to perform a graceful shutdown rather than an immediate destroy, aiming to reduce abrupt termination during cleanup.

Changes:

• Replace extHostSocket.destroy() with a conditional extHostSocket.end() on dispose.
• Add guards to avoid ending an already-destroyed or already-ended socket.

[dmitrivMS]

Agreed!

[dmitrivMS]

This can be a helper, something like "gracefulSocketEnd" which can potentially be reused

[SimonSiefke]

Perhaps? I'm not actually sure what's the right way to gracefully close a NodeJS socket. The code with socket.end() just seemed to work.

Can socket.end leave the socket half-open forever if the other side never closes the socket? I don't know...

There seem to be other places where, on socket.end event, after 30 seconds, it destroys the socket like

vscode/src/vs/base/parts/ipc/node/ipc.net.ts

Line 143 in 1f03fed

endTimeoutHandle = setTimeout(() => socket.destroy(), socketEndTimeoutMs);

I just looked at the NodeJS docs, and there is also a method socket.destroySoon, which looks like even better:

Destroys the socket after all data is written. If the 'finish' event was already emitted the socket is destroyed immediately. If the socket is still writable it implicitly calls socket.end().

If I would make this PR again I'd probably choose socket.destroySoon

[dmitrivMS]

Well, perhaps a follow up PR? I think a timeout race would still be useful in this case.

[SimonSiefke]

(made another small change to try to fix windows ci)

[connor4312]

thank you!

[dmitrivMS]

nit: isBenignSocketTeardownError name would probably be better here

[dmitrivMS]

@SimonSiefke Thanks a lot! Please take a look at some feedback