fix(share): propagate closed to firehose sources

spec/operators/multicast-spec.ts

@@ -821,47 +821,4 @@ describe('multicast', () => {
         );
     });
   });
-
-  // TODO: fix firehose unsubscription
-  // AFAICT, it's not possible for multicast observables to support ASAP
-  // unsubscription from synchronous firehose sources. The problem is that the
-  // chaining of the closed 'signal' is broken by the subject. For example,
-  // here:
-  //
-  // https://github.com/ReactiveX/rxjs/blob/2d5e4d5bd7b684a912485e1c1583ba3d41c8308e/src/internal/operators/multicast.ts#L53
-  //
-  // The subject is passed to subscribe. However, in the subscribe
-  // implementation a SafeSubscriber is created with the subject as the
-  // observer:
-  //
-  // https://github.com/ReactiveX/rxjs/blob/2d5e4d5bd7b684a912485e1c1583ba3d41c8308e/src/internal/Observable.ts#L210
-  //
-  // That breaks the chaining of closed - i.e. even if the unsubscribe is
-  // called on the subject, closing it, the SafeSubscriber's closed property
-  // won't reflect that.
-  it.skip('should stop listening to a synchronous observable when unsubscribed', () => {
-    const sideEffects: number[] = [];
-    const synchronousObservable = new Observable<number>((subscriber) => {
-      // This will check to see if the subscriber was closed on each loop
-      // when the unsubscribe hits (from the `take`), it should be closed
-      for (let i = 0; !subscriber.closed && i < 10; i++) {
-        sideEffects.push(i);
-        subscriber.next(i);
-      }
-    });
-
-    synchronousObservable
-      .pipe(
-        multicast(
-          () => new Subject<number>(),
-          (source) => source
-        ),
-        take(3)
-      )
-      .subscribe(() => {
-        /* noop */
-      });
-
-    expect(sideEffects).to.deep.equal([0, 1, 2]);
-  });
 });

spec/operators/refCount-spec.ts

@@ -114,25 +114,4 @@ describe('refCount', () => {
     expect(arr[0]).to.equal('the number one');
     expect(arr[1]).to.equal('the number two');
   });
-
-  // TODO: fix firehose unsubscription
-  it.skip('should stop listening to a synchronous observable when unsubscribed', () => {
-    const sideEffects: number[] = [];
-    const synchronousObservable = new Observable<number>(subscriber => {
-      // This will check to see if the subscriber was closed on each loop
-      // when the unsubscribe hits (from the `take`), it should be closed
-      for (let i = 0; !subscriber.closed && i < 10; i++) {
-        sideEffects.push(i);
-        subscriber.next(i);
-      }
-    });
-
-    synchronousObservable.pipe(
-      multicast(() => new Subject<number>()),
-      refCount(),
-      take(3),
-    ).subscribe(() => { /* noop */ });
-
-    expect(sideEffects).to.deep.equal([0, 1, 2]);
-  });
 });

spec/operators/share-spec.ts

@@ -427,8 +427,7 @@ describe('share', () => {
       });
     });
 
-    // TODO: fix firehose unsubscription
-    it.skip('should stop listening to a synchronous observable when unsubscribed', () => {
+    it('should stop listening to a synchronous observable when unsubscribed', () => {
       const sideEffects: number[] = [];
       const synchronousObservable = new Observable<number>((subscriber) => {
         // This will check to see if the subscriber was closed on each loop

spec/operators/shareReplay-spec.ts

@@ -347,25 +347,6 @@ describe('shareReplay', () => {
     });
   });
 
-  // TODO: fix firehose unsubscription
-  it.skip('should stop listening to a synchronous observable when unsubscribed', () => {
-    const sideEffects: number[] = [];
-    const synchronousObservable = new Observable<number>((subscriber) => {
-      // This will check to see if the subscriber was closed on each loop
-      // when the unsubscribe hits (from the `take`), it should be closed
-      for (let i = 0; !subscriber.closed && i < 10; i++) {
-        sideEffects.push(i);
-        subscriber.next(i);
-      }
-    });
-
-    synchronousObservable.pipe(shareReplay(), take(3)).subscribe(() => {
-      /* noop */
-    });
-
-    expect(sideEffects).to.deep.equal([0, 1, 2]);
-  });
-
   const FinalizationRegistry = (global as any).FinalizationRegistry;
   if (FinalizationRegistry) {
     it('should not leak the subscriber for sync sources', (done) => {

src/internal/operators/share.ts

@@ -112,6 +112,26 @@ export function share<T>(options?: ShareConfig<T>): OperatorFunction<T, T> {
     // Create the subject if we don't have one yet.
     subject = subject ?? connector();
 
+    // Add the teardown directly to the subscriber - instead of returning it -
+    // so that the handling of the subscriber's unsubscription will be wired
+    // up _before_ the subscription to the source occurs. This is done so that
+    // the assignment to the source connection's `closed` property will be seen
+    // by synchronous firehose sources.
+    subscriber.add(() => {
+      refCount--;
+
+      // If we're resetting on refCount === 0, and it's 0, we only want to do
+      // that on "unsubscribe", really. Resetting on error or completion is a different
+      // configuration.
+      if (resetOnRefCountZero && !refCount && !hasErrored && !hasCompleted) {
+        // We need to capture the connection before
+        // we reset (if we need to reset).
+        const conn = connection;
+        reset();
+        conn?.unsubscribe();
+      }
+    });
+
     // The following line adds the subscription to the subscriber passed.
     // Basically, `subscriber === subject.subscribe(subscriber)` is `true`.
     subject.subscribe(subscriber);
@@ -147,21 +167,5 @@ export function share<T>(options?: ShareConfig<T>): OperatorFunction<T, T> {
       });
       from(source).subscribe(connection);
     }
-
-    // This is also added to `subscriber`, technically.
-    return () => {
-      refCount--;
-
-      // If we're resetting on refCount === 0, and it's 0, we only want to do
-      // that on "unsubscribe", really. Resetting on error or completion is a different
-      // configuration.
-      if (resetOnRefCountZero && !refCount && !hasErrored && !hasCompleted) {
-        // We need to capture the connection before
-        // we reset (if we need to reset).
-        const conn = connection;
-        reset();
-        conn?.unsubscribe();
-      }
-    };
   });
 }