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fix(AsyncSubject): properly emits values during reentrant subscriptions #6522

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Jul 14, 2021
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fix(AsyncSubject): properly emits values during reentrant subscriptions #6522

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23 changes: 22 additions & 1 deletion spec/subjects/AsyncSubject-spec.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -211,7 +211,7 @@ describe('AsyncSubject', () => {
expect(calls).to.equal(1);
});

it('should not be reentrant via next', () => {
it('should not be reentrant via next', () => {
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We need to get prettier going on this file. This was just moving a space that was bothering me. haha.

const subject = new AsyncSubject<number>();
let calls = 0;
subject.subscribe({
Expand All @@ -229,4 +229,25 @@ describe('AsyncSubject', () => {

expect(calls).to.equal(1);
});

it('should allow reentrant subscriptions', () => {
const subject = new AsyncSubject<number>()
let results: any[] = [];

subject.subscribe({
next: (value) => {
subject.subscribe({
next: value => results.push('inner: ' + (value + value)),
complete: () => results.push('inner: done')
});
results.push('outer: ' + value);
},
complete: () => results.push('outer: done')
});

subject.next(1);
expect(results).to.deep.equal([]);
subject.complete();
expect(results).to.deep.equal(['inner: 2', 'inner: done', 'outer: 1', 'outer: done']);
});
});
4 changes: 2 additions & 2 deletions src/internal/AsyncSubject.ts
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Expand Up @@ -14,10 +14,10 @@ export class AsyncSubject<T> extends Subject<T> {

/** @internal */
protected _checkFinalizedStatuses(subscriber: Subscriber<T>) {
const { hasError, _hasValue, _value, thrownError, isStopped } = this;
const { hasError, _hasValue, _value, thrownError, isStopped, _isComplete } = this;
if (hasError) {
subscriber.error(thrownError);
} else if (isStopped) {
} else if (isStopped || _isComplete) {
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Basically, there's a temporal space where we're _isComplete, but not isStopped while we're nexting to consumers in our complete() method. If someone subscribes during that, we end up hitting this code, and if we're only checking isStopped it's not "stopped" yet, so we didn't notify the consumer.

_hasValue && subscriber.next(_value!);
subscriber.complete();
}
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