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  1. Node.js Driver
  2. NODE-5138

Investigate: Are parallel invocations of MongoClient.close safe?

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    • Type: Icon: Question Question
    • Resolution: Unresolved
    • Priority: Icon: Minor - P4 Minor - P4
    • None
    • Affects Version/s: None
    • Component/s: Connection Layer

      Question

      Is it possible that invoking close more than once in parallel could lead to an error? (somewhat like a double free). Should this be something the driver handles similar to NODE-5106 with connect?

      I'm wondering if `.close` also has a parallelism issue. Supposedly we could be calling `.end` on sockets more than once because as the first "`client.close`" promise is pending the I/O for socket closure the next promise could also synchronously reach the `.end` invocation.

      This may in fact not be the case but if it is we'll want to also fix that.

      I contrived an example, I have to use sleep 1ms to make the promises offset by a bit but I would imagine in real world scenario a delay like that could occur depending on what else is in the event loop.

      Example script that calls .end in parallel

      import { once } from 'events';
import { Socket } from 'net';
import { setTimeout as sleep } from 'timers/promises';
import { promisify } from 'util';

const socket = new Socket();
const willConnect = once(socket, 'connect');
socket.connect({ host: '127.0.0.1', port: 2390 }).setDefaultEncoding('utf8').setEncoding('utf8');
await willConnect;

await promisify(callback => socket.write('hello\n', callback))();

// MongoClient .close in parallel
await Promise.all([
  promisify(callback => socket.end(callback))(),
  sleep(1).then(() => promisify(callback => socket.end(callback))())
]);

      Error [ERR_STREAM_ALREADY_FINISHED]: Cannot call end after a stream was finished
    at new NodeError (node:internal/errors:393:5)
    at Writable.end (node:internal/streams/writable:637:11)
    at Socket.end (node:net:691:31)
  code: 'ERR_STREAM_ALREADY_FINISHED'
}

            Assignee:
            Unassigned Unassigned
            Reporter:
            neal.beeken@mongodb.com Neal Beeken
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              Created:
              Updated: