Can we achieve parallel polling with this library

[siddharthpal]

`
import { timer as observableTimer, Subscription, throwError } from 'rxjs';

import { takeWhile, tap, catchError, exhaustMap } from 'rxjs/operators';
import { Injectable, Inject } from '@angular/core';
import { HttpClient, HttpErrorResponse } from '@angular/common/http';
import { REPORT_CONFIG_TOKEN } from '../configs/report.config';

@Injectable()
export class PollingService {

private pollSubscriptions: Subscription;
private defaultPollTime: number = 2000;
constructor(
    private http: HttpClient,
    @Inject(REPORT_CONFIG_TOKEN) private config: any
) {
    this.pollSubscriptions = new Subscription();
}

pollRequest<T>(
    url: string,
    updateStatus: any,
    pollWhileCondition: Function,
    pollErrorCallback?: Function,
    onPollingSuccessCallback?: Function,
    timer = this.defaultPollTime
) {
    if (this.pollSubscriptions.closed) {
        this.pollSubscriptions = new Subscription();
    }
    this.pollSubscriptions.add(observableTimer(0, timer).pipe(
        exhaustMap(() => this.http.get<T>(url, { headers: this.config.requestConfig.headers }).pipe(
            catchError((err: HttpErrorResponse) => {
                pollErrorCallback(err);
                return throwError(err);
            }))),
        tap(updateStatus),
        takeWhile(data => pollWhileCondition(data)))
        .subscribe());
}

stopPolling(): void {
    this.pollSubscriptions.unsubscribe();
}

}
`
I am able to poll for multiple urls simultaneously. But can I use this library so that I can meet the following requirements:

1. If a url which is polled gets failed then how can we retry that poll url with a delay of 3(n) secs for 3 times(I am okay with any strategy but should have some delay)?
2. Can we make sure that same urls are not polled at any point of time?
3. If we pass retryAttempts can we throw that error? But stream should not break!