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fix(share): Prevent setup/reset race condition in share with refCount #7005

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merged 2 commits into from
Jul 8, 2022

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Description: Fixes the bug described in #6760, which seems to be a race condition.

The conditions are as such:

  • Have an observable that emits immediately, but does not complete (eg. a BehaviorSubject, or something with startWith)
  • Share it with shareReplay (or any share with refCount: true)
  • Subscribe multiple times simultaneously, then unsubscribe immediately (can happen with firstValueFrom)
  • The shared observable then gets into a bad state where it stays subscribed to the source observable but doesn't emit new values when next subscribed to.

The reason this happens is because share adds the reset subscription before subscribing to the source. As a result, if we subscribe and unsubscribe simultaneously, the reset block can actually run before subscribing to the source. When it gets reset, the connection state gets reset as well, and it subscribes to the source again even though it's already been reset.

In the PR, I've fixed it via adding an extra check before subscribing to make sure we actually need to subscribe to the source. I feel like this is only patches over the issue and some other edge case may still be broken, but there are some comments in the code saying that the reset subscription needs to be before the source subscription, so I didn't want to move anything else around.

I added a test as well, though it tests a symptom (an excess subscription) rather than the real impact (doesn't emit again later). Couldn't get the latter working.

BREAKING CHANGE: No

Related issue (if exists): #6760

@jkossis
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jkossis commented Jul 7, 2022

@benlesh curious what your thoughts are on this. It looks like this may have cropped up with the simplification of multicast operators in 7.x.

@jkossis
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jkossis commented Jul 8, 2022

@benlesh I noticed your comment from earlier (perhaps it was deleted?), but I am not 100% convinced this is a bug with combineLatest. Or at least, that may be a separate bug. If you look through the linked issue, this race behavior can be elicited without the use of combineLatest.

In my case, I noticed it while using shareReplay on the server-side for broadcasting events to clients over gql subscriptions. Clients that connect/disconnect around the same time can run into this behavior, where it gets stuck (nothing is emitted to the "late" subscriber).

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benlesh commented Jul 8, 2022

Yeah. Exploring this, I see the issue. It also looks like it's time for me to clean up share (again) 😩 . I experimented with it a bit, and I think this is the best fix for now. Thank you.

@benlesh benlesh merged commit 5d4c1d9 into ReactiveX:master Jul 8, 2022
@jkossis
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jkossis commented Jul 8, 2022

@benlesh is there any way to get a minor/patch publish for including this change on 7.x?

EDIT
Just noticed this commit in your fork. I suppose you'd want to get that merged before considering a version bump.

crapStone pushed a commit to Calciumdibromid/CaBr2 that referenced this pull request Jul 11, 2022
This PR contains the following updates:

| Package | Type | Update | Change |
|---|---|---|---|
| [rxjs](https://rxjs.dev) ([source](https://github.com/reactivex/rxjs)) | dependencies | patch | [`7.5.5` -> `7.5.6`](https://renovatebot.com/diffs/npm/rxjs/7.5.5/7.5.6) |

---

### Release Notes

<details>
<summary>reactivex/rxjs</summary>

### [`v7.5.6`](https://github.com/reactivex/rxjs/blob/HEAD/CHANGELOG.md#&#8203;756-httpsgithubcomreactivexrxjscompare755756-2022-07-11)

[Compare Source](ReactiveX/rxjs@7.5.5...7.5.6)

##### Bug Fixes

-   **share:** No longer results in a bad-state observable in an edge case where a synchronous source was shared and refCounted, and the result is subscribed to twice in a row synchronously. ([#&#8203;7005](ReactiveX/rxjs#7005)) ([5d4c1d9](ReactiveX/rxjs@5d4c1d9))
-   **share & connect:** `share` and `connect` no longer bundle scheduling code by default ([#&#8203;6873](ReactiveX/rxjs#6873)) ([9948dc2](ReactiveX/rxjs@9948dc2)), closes [#&#8203;6872](ReactiveX/rxjs#6872)
-   **exhaustAll:** Result will now complete properly when flattening all synchronous observables. ([#&#8203;6911](ReactiveX/rxjs#6911)) ([3c1c6b8](ReactiveX/rxjs@3c1c6b8)), closes [#&#8203;6910](ReactiveX/rxjs#6910)
-   **TypeScript:** Now compatible with TypeScript 4.6 type checks ([#&#8203;6895](ReactiveX/rxjs#6895)) ([fce9aa1](ReactiveX/rxjs@fce9aa1))

</details>

---

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crapStone pushed a commit to Calciumdibromid/CaBr2 that referenced this pull request Dec 23, 2022
This PR contains the following updates:

| Package | Type | Update | Change |
|---|---|---|---|
| [rxjs](https://rxjs.dev) ([source](https://github.com/reactivex/rxjs)) | dependencies | minor | [`7.5.7` -> `7.8.0`](https://renovatebot.com/diffs/npm/rxjs/7.5.7/7.8.0) |

---

### Release Notes

<details>
<summary>reactivex/rxjs</summary>

### [`v7.8.0`](https://github.com/reactivex/rxjs/blob/HEAD/CHANGELOG.md#&#8203;780-httpsgithubcomreactivexrxjscompare770780-2022-12-15)

[Compare Source](ReactiveX/rxjs@7.7.0...7.8.0)

##### Features

-   **buffer:** `closingNotifier` now supports any `ObservableInput` ([#&#8203;7073](ReactiveX/rxjs#7073)) ([61b877a](ReactiveX/rxjs@61b877a))
-   **delayWhen:** `delayWhen`'s `delayDurationSelector` now supports any `ObservableInput` ([#&#8203;7049](ReactiveX/rxjs#7049)) ([dfd95db](ReactiveX/rxjs@dfd95db))
-   **sequenceEqual:** `compareTo` now supports any `ObservableInput` ([#&#8203;7102](ReactiveX/rxjs#7102)) ([d501961](ReactiveX/rxjs@d501961))
-   **share:** `ShareConfig` factory properties now supports any `ObservableInput` ([#&#8203;7093](ReactiveX/rxjs#7093)) ([cc3995a](ReactiveX/rxjs@cc3995a))
-   **skipUntil:** `notifier` now supports any `ObservableInput` ([#&#8203;7091](ReactiveX/rxjs#7091)) ([60d6c40](ReactiveX/rxjs@60d6c40))
-   **window:** `windowBoundaries` now supports any `ObservableInput` ([#&#8203;7088](ReactiveX/rxjs#7088)) ([8c4347c](ReactiveX/rxjs@8c4347c))

### [`v7.7.0`](https://github.com/reactivex/rxjs/blob/HEAD/CHANGELOG.md#&#8203;770-httpsgithubcomreactivexrxjscompare760770-2022-12-15)

[Compare Source](ReactiveX/rxjs@7.6.0...7.7.0)

##### Features

-   **distinct:** `flush` argument now supports any `ObservableInput` ([#&#8203;7081](ReactiveX/rxjs#7081)) ([74c9ebd](ReactiveX/rxjs@74c9ebd))
-   **repeatWhen:** `notifier` supports `ObservableInput` ([#&#8203;7103](ReactiveX/rxjs#7103)) ([8f1b976](ReactiveX/rxjs@8f1b976))
-   **retryWhen:** `notifier` now supports any `ObservableInput` ([#&#8203;7105](ReactiveX/rxjs#7105)) ([794f806](ReactiveX/rxjs@794f806))
-   **sample:** `notifier` now supports any `ObservableInput` ([#&#8203;7104](ReactiveX/rxjs#7104)) ([b18c2eb](ReactiveX/rxjs@b18c2eb))

### [`v7.6.0`](https://github.com/reactivex/rxjs/blob/HEAD/CHANGELOG.md#&#8203;760-httpsgithubcomreactivexrxjscompare757760-2022-12-03)

[Compare Source](ReactiveX/rxjs@7.5.7...7.6.0)

##### Bug Fixes

-   **schedulers:** no longer cause TypeScript build failures when Node types aren't included ([c1a07b7](ReactiveX/rxjs@c1a07b7))
-   **types:** Improved subscribe and tap type overloads ([#&#8203;6718](ReactiveX/rxjs#6718)) ([af1a9f4](ReactiveX/rxjs@af1a9f4)), closes [#&#8203;6717](ReactiveX/rxjs#6717)

##### Features

-   **onErrorResumeNextWith:** renamed `onErrorResumeNext` and exported from the top level. (`onErrorResumeNext` operator is stil available, but deprecated) ([#&#8203;6755](ReactiveX/rxjs#6755)) ([51e3b2c](ReactiveX/rxjs@51e3b2c))

#### [7.5.7](ReactiveX/rxjs@7.5.6...7.5.7) (2022-09-25)

##### Bug Fixes

-   **schedulers:** improve performance of animationFrameScheduler and asapScheduler ([#&#8203;7059](ReactiveX/rxjs#7059)) ([c93aa60](ReactiveX/rxjs@c93aa60)), closes [#&#8203;7017](ReactiveX/rxjs#7017), related to [#&#8203;7018](ReactiveX/rxjs#7018) and [#&#8203;6674](ReactiveX/rxjs#6674)

##### Performance Improvements

-   **animationFrames:** uses fewer Subscription instances ([#&#8203;7060](ReactiveX/rxjs#7060)) ([2d57b38](ReactiveX/rxjs@2d57b38)), closes [#&#8203;7018](ReactiveX/rxjs#7018)

#### [7.5.6](ReactiveX/rxjs@7.5.5...7.5.6) (2022-07-11)

##### Bug Fixes

-   **share:** No longer results in a bad-state observable in an edge case where a synchronous source was shared and refCounted, and the result is subscribed to twice in a row synchronously. ([#&#8203;7005](ReactiveX/rxjs#7005)) ([5d4c1d9](ReactiveX/rxjs@5d4c1d9))
-   **share & connect:** `share` and `connect` no longer bundle scheduling code by default ([#&#8203;6873](ReactiveX/rxjs#6873)) ([9948dc2](ReactiveX/rxjs@9948dc2)), closes [#&#8203;6872](ReactiveX/rxjs#6872)
-   **exhaustAll:** Result will now complete properly when flattening all synchronous observables. ([#&#8203;6911](ReactiveX/rxjs#6911)) ([3c1c6b8](ReactiveX/rxjs@3c1c6b8)), closes [#&#8203;6910](ReactiveX/rxjs#6910)
-   **TypeScript:** Now compatible with TypeScript 4.6 type checks ([#&#8203;6895](ReactiveX/rxjs#6895)) ([fce9aa1](ReactiveX/rxjs@fce9aa1))

#### [7.5.5](ReactiveX/rxjs@7.5.4...7.5.5) (2022-03-08)

##### Bug Fixes

-   **package:** add types to exports ([#&#8203;6802](ReactiveX/rxjs#6802)) ([3750f75](ReactiveX/rxjs@3750f75))
-   **package:** add `require` export condition ([#&#8203;6821](ReactiveX/rxjs#6821)) ([c8955e4](ReactiveX/rxjs@c8955e4))
-   **timeout:** no longer will timeout when receiving the first value synchronously ([#&#8203;6865](ReactiveX/rxjs#6865)) ([2330c96](ReactiveX/rxjs@2330c96)), closes [#&#8203;6862](ReactiveX/rxjs#6862)

##### Performance Improvements

-   Don't clone observers unless you have to ([#&#8203;6842](ReactiveX/rxjs#6842)) ([3289d20](ReactiveX/rxjs@3289d20))

#### [7.5.4](ReactiveX/rxjs@7.5.3...7.5.4) (2022-02-09)

##### Performance Improvements

-   removed code that would `bind` functions passed with observers to `subscribe`. ([#&#8203;6815](ReactiveX/rxjs#6815)) ([fb375a0](ReactiveX/rxjs@fb375a0)), closes [#&#8203;6783](ReactiveX/rxjs#6783)

#### [7.5.3](ReactiveX/rxjs@7.5.2...7.5.3) (2022-02-08)

##### Bug Fixes

-   **subscribe:** allow interop with Monio and other libraries that patch function bind ([0ab91eb](ReactiveX/rxjs@0ab91eb)), closes [#&#8203;6783](ReactiveX/rxjs#6783)

#### [7.5.2](ReactiveX/rxjs@7.5.1...7.5.2) (2022-01-11)

##### Bug Fixes

-   operators that ignore input values now use `unknown` rather than `any`, which should resolve issues with eslint no-unsafe-argument ([#&#8203;6738](ReactiveX/rxjs#6738)) ([67cb317](ReactiveX/rxjs@67cb317)), closes [#&#8203;6536](ReactiveX/rxjs#6536)
-   **ajax:** crossDomain flag deprecated and properly reported to consumers ([#&#8203;6710](ReactiveX/rxjs#6710)) ([7fd0575](ReactiveX/rxjs@7fd0575)), closes [#&#8203;6663](ReactiveX/rxjs#6663)

#### [7.5.1](ReactiveX/rxjs@7.5.0...7.5.1) (2021-12-28)

##### Bug Fixes

-   export supporting interfaces from top-level `rxjs` site. ([#&#8203;6733](ReactiveX/rxjs#6733)) ([299a1e1](ReactiveX/rxjs@299a1e1))

</details>

---

### Configuration

📅 **Schedule**: Branch creation - At any time (no schedule defined), Automerge - At any time (no schedule defined).

🚦 **Automerge**: Disabled by config. Please merge this manually once you are satisfied.

♻ **Rebasing**: Whenever PR becomes conflicted, or you tick the rebase/retry checkbox.

🔕 **Ignore**: Close this PR and you won't be reminded about this update again.

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 - [ ] <!-- rebase-check -->If you want to rebase/retry this PR, check this box

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Co-authored-by: cabr2-bot <cabr2.help@gmail.com>
Reviewed-on: https://codeberg.org/Calciumdibromid/CaBr2/pulls/1668
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