When a subject is multicasted, first subscription next event in its observer synchronously, the second subscription will get the reverse sequence of event

[sanmaopep]

Describe the bug

When a subject is subscribed into two subscription: a & b

In subscription a:
console a value
next a value synchronously and recursively (for instance 1, 2, 3, 4, 5)

In subscription b:
console a value

and subject next a value 1 so 1 will be multicasted to a & b

And subscription a will console 1, 2, 3, 4, 5, which meets the demand
But subscription b will console 5, 4, 3, 2, 1, in this case the normal event sequence is reversed

Expected behavior

subscription a & b console the same event sequence

subscription a will console 1, 2, 3, 4, 5
subscription b will also console 1, 2, 3, 4, 5

Reproduction code

const test$ = new Subject();

// a subscription
test$.subscribe((current) => {
  console.log('a', current);
  if(current < 5) {
    test$.next(current + 1)
  }
})

// b subscription
test$.subscribe((current) => {
  console.log('b', current);
})

test$.next(1);

// a 1
// a 2
// a 3
// a 4
// a 5

// b 5
// b 4
// b 3
// b 2
// b 1

### Reproduction URL

_No response_

### Version

7.2.0

### Environment

_No response_

### Additional context

_No response_

[iskalyakin]

Looks like current behavior is correct. "next" is called synchronously from "a", and because all its callbacks are called synchronously too, all these calls take place before first callback call in "b".

[benlesh]

Hi @sanmaopep — 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