v7 finalize broken for multiplexed resource handling

[RohanHart]

Describe the bug

The change to make finalize execute in the order they're defined in the pipeline (#5433) breaks resource handling when the resource is multiplexed and the downstream subscriptions have their own finalization logic which uses the multiplexed resource.

Expected behavior

Rather than return to the pre-7 behaviour and another breaking change this could be a config option to finalize or make the "block" the finalizer apples to explicit with some bracketing operator.

Reproduction code

import { Subject } from 'rxjs';
import { filter, finalize, share } from 'rxjs/operators';

let resource = console.log;

const source = new Subject<number>();
const multiplex = source.pipe(
  finalize(() => {
    resource('closed');
    resource = undefined;
  }),
  share( /* { resetOnRefCountZero: () => timer(0) } */ )
);

const client = (m: number) => {
  resource('start ' + m);
  return multiplex.pipe(
    filter((v) => v % m === 0),
    finalize(() => {
      resource('stop ' + m);
    }),
    share()
  );
};

const client1 = client(2);
const l1 = client1.subscribe(console.log);
const l2 = client1.subscribe(console.log);

const l3 = client(3).subscribe(console.log);

source.next(2);
source.next(3);

l1.unsubscribe();

source.next(6);

l3.unsubscribe();

source.next(12);

l2.unsubscribe();

// Expected
//
// start 2
// start 3
// 2
// 2
// 3
// 6
// stop 3
// 12
// stop 2
// closed

// Actual
//
// start 2
// start 3
// 2
// 2
// 3
// 6
// stop 3
// 12
// closed
//
// throws: 1 errors occurred during unsubscription: TypeError: resource is not a function

Reproduction URL

https://stackblitz.com/edit/typescript-886qi6?file=index.ts

Version

7.4.0

Environment

No response

Additional context

This behaviour can be worked around by making the multiplexed observable's share reset asynchronously share({ resetOnRefCountZero: () => timer(0) }) but that's a bit obscure.

[benlesh]

Hi @RohanHart — thank you for taking the time to open this issue and for sharing your thoughtful feedback with the RxJS project. I’m sorry it took us so long to respond. Given how much time has passed and the lack of recent activity, I’m going to close this for now so the tracker reflects the work we’re likely to act on. If this is still relevant on a current RxJS release, please feel welcome to open a new issue with updated context and a reproduction. Thank you again for your contribution and patience.

— Ben

[RohanHart]

Hi @benlesh

No worries, I can't say whether this is still relevant as we've been using the workaround since that time.

cheers