重置 RxJS concatMap 而不完成外部 Subject

Question

I'm using a concatMap to handle multiple requests to an API, where I want each request batch to be completed before the next batch is processed. The concatMap works as expected when triggering the flow with callSubject.next(requestData)

The problem: for certain types of requestData I want to cancel any in-flight http calls, and reset the concatMap . Cancelling the httpClient calls that are occurring within the getAll function is handy enough (I have a takeUntil that does that - not shown), but the concatMap may still have a number of queued up requests that will then be processed.

Is there a way to reset the concatMap without completing the callSubject Subject?

Note: if I trigger unsubscribeCallSubject$.next() this clears the concatmap, but also completes the callSubject, which means it can no longer be used with callSubject.next(reqData)

// callSubject is a Subject which can be triggered multiple times
callSubject
  .pipe(
    concatMap((req) => {
      // getAll makes multiple httpClient calls in sequence
      return getAll(req).pipe(
        catchError((err) => {
          // prevent callSubject completing on http error
          return of(err);
        })
      );
    }),
    takeUntil(unsubscribeCallSubject$)
  )
  .subscribe(
    (v) => log("callSubject: next handler", v),
    (e) => log("callSubject: error", e),
    () => log("callSubject: complete")
  );

Answer 1

If I understand the problem right, you could try an approach which uses switchMap any time unsubscribeCallSubject$ emits.

The code would look something like this

unsubscribeCallSubject$.pipe(
  // use startWith to start the stream with something
  startWith('anything'),
  // switchMap any time unsubscribeCallSubject$ emits, which will unsubscribe 
  // any Observable within the following concatMap
  switchMap(() => callSubject$),
  // concatMap as in your example
  concatMap((req) => {
      // getAll makes multiple httpClient calls in sequence
      return getAll(req).pipe(
        catchError((err) => {
          // prevent callSubject completing on http error
          return of(err);
        })
      );
    }),
)
.subscribe(
    (v) => log("callSubject: next handler", v),
    (e) => log("callSubject: error", e),
    () => log("callSubject: complete")
);

To be honest I have not tested this approach and so I am not sure whether it solves your problem, but if I have understood your problem right, this could work.