Use Case

As a MongoDB user who is calling MongoClient.connect on an un-selectable cluster
I want MongoClient.connect to hold the Node.js process open until serverSelectionTimeoutMS expires
So that I can see the rejected error.

The new Timeout abstraction unref-s it's timer which may make sense for CSOT. On your very first connect call the serverSelection ref-ed setTimeout call is what keeps Node.js open.

User Impact

• The following sample code exits immediately with "Warning: Detected unsettled top-level await"

import { MongoClient } from 'mongodb';

// real set name: repl0
const cs = 'mongodb://127.0.0.1:27017,127.0.0.1:27018,127.0.0.1:27019/&replicaSet=asdf';
process.on('exit', () => console.log('exiting'));
const client = await MongoClient.connect(cs);
console.log('connected');
await client.close();

Dependencies

• serverSelectionTimeoutMS logic
• Timeout ref/unref

Unknowns

• None

Acceptance Criteria

Implementation Requirements

• Ref the timer in Timeout
  • If it is possible only do this when we are connecting for the first time? (check the MongoClient) otherwise do it always and revisit ref-ing / clearing for CSOT

Testing Requirements

• Determine: What is the best programmatic way to determine if Node.js would exit?
  • process _activeHandles? process.on('beforeExit')
• Assert MongoClient.connect keeps Node.js running until it succeeds or fails.

Documentation Requirements

• None

Follow Up Requirements

• Consider refactoring auto-connect: monitors should be "always on". Is this caused by the process.nextTick that surrounds requestCheck? if we called requestCheck directly then would server selection have created sockets thus keeping Node open?
• Add testing to verify that this behaviour does not return in subsequent changes (NODE-6152)