detached not working as expected

[nkomonen-amazon]

My original task is that if the LS client (Extension Host) terminates gracefully or non gracefully, I don't want my Language Server to terminate. I want the LS to decide for itself when to terminate.

• It looks like the detached flag should have been the solution but I am not able to get it to working.
• I've also tried:

// based on this comment: https://github.com/microsoft/vscode-languageserver-node/issues/857#issuecomment-980003467
{ initializationOptions: { processId: '' }, }

Minimal Repro

These are the following steps to setup for repro.

• I am using the lsp-sample project
• Replace server/src/server.ts with the following

import {
	createConnection,
	NotificationType,
	ProposedFeatures} from 'vscode-languageserver/node';

const Heartbeat: NotificationType<undefined> = new NotificationType<undefined>('heartbeat');

const connection = createConnection(ProposedFeatures.all);

connection.onInitialize(() => {
	connection.console.log(`PPID ${process.ppid}`);
        // I would expect this PID to stay alive after the PPID above is terminated, but it does not
	connection.console.log(`PID ${process.pid}`);
	return {
		capabilities: {}
	};
});

connection.onNotification(Heartbeat, () => {
	connection.console.log('heartbeat');
});

connection.listen();

• Replace client/src/extension.ts

import * as path from 'path';
import { ExtensionContext } from 'vscode';

import {
	Executable,
	LanguageClient,
	NotificationType,
	TransportKind
} from 'vscode-languageclient/node';

let client: LanguageClient;
const Heartbeat: NotificationType<undefined> = new NotificationType<undefined>('heartbeat');

export async function activate(context: ExtensionContext) {
	const serverModule = context.asAbsolutePath(
		path.join('server', 'out', 'server.js')
	);

	// `detached` is not available in ForkOptions, so I must do it this way
	const serverOptions: Executable = {
		command: 'node', args: [serverModule], transport: TransportKind.stdio, options: { detached: true }
	};

	// Create the language client and start the client.
	client = new LanguageClient(
		'languageServerExample',
		'Language Server Example',
		serverOptions,
		// Tried this based on this comment: https://github.com/microsoft/vscode-languageserver-node/issues/857#issuecomment-980003467
		{ initializationOptions: { processId: '' }, }
	);

	await client.start();


	// Send a heartbeat every interval to show we are connected to LSP
	setInterval(async () => {
		await client.sendNotification(Heartbeat);
	}, 5000);
}

export function deactivate(): Thenable<void> | undefined {
	return undefined;
}

• Run the extension in Debug Mode
• Note the PPID+PID in the logs of the Language Server Example Output logs
• Kill the PPID (Ext host)
• The PID unexpectedly terminates shortly after.

Expected

I would expect that with detached: true killing the Ext Host would not impact the Language Server.

Is there any configuration that I am missing? Maybe something that needs to be configured on the LS side?

[dbaeumer]

Which OS are you on. The detached support depends on NodeJS detach support and how it behaves varies a little depending on the OS. Does this work correctly for you when you use the pure NodeJS API (https://nodejs.org/api/child_process.html#optionsdetached)?

[nkomonen-amazon]

I'm using MacOS.

Does this work correctly for you when you use the pure NodeJS API

Yup, I tried spawn('node', [ myTestPath ], { detached: false }) and can confirm that it did not terminate when I killed the parent process. But oddly, with detached: false, the child process still does not terminate even though I think it should.

When using the language server example linked above, the LS still terminates when I kill the parent.

[dbaeumer]

Whether a process terminates or not if the parent process terminates depends on the OS. To my knowledge Windows always kills child processes (unless detached: true) whereas Linux / Mac assign the process to a process group and they don't terminate. This is why at some point I added code to auto terminate the server (https://github.com/microsoft/vscode-languageserver-node/blob/dbaeumer/lexical-skunk-aquamarine/server/src/node/main.ts#L46).

I would need to change this code to only do that when detached: false.

[nkomonen-amazon]

Makes sense with what I've been seeing.

Any idea when a change could fit in your schedule?