rxjs/src/operators/refCount.ts

Reactive Extensions for modern JavaScript

import { Operator } from '../Operator';
import { Subscriber } from '../Subscriber';
import { Subscription, TeardownLogic } from '../Subscription';
import { MonoTypeOperatorFunction } from '../interfaces';
import { ConnectableObservable } from '../observable/ConnectableObservable';
import { Observable } from '../Observable';

export function refCount<T>(): MonoTypeOperatorFunction<T> {
  return function refCountOperatorFunction(source: ConnectableObservable<T>): Observable<T> {
    return source.lift(new RefCountOperator(source));
  };
}

class RefCountOperator<T> implements Operator<T, T> {
  constructor(private connectable: ConnectableObservable<T>) {
  }
  call(subscriber: Subscriber<T>, source: any): TeardownLogic {

    const { connectable } = this;
    (<any> connectable)._refCount++;

    const refCounter = new RefCountSubscriber(subscriber, connectable);
    const subscription = source.subscribe(refCounter);

    if (!refCounter.closed) {
      (<any> refCounter).connection = connectable.connect();
    }

    return subscription;
  }
}

class RefCountSubscriber<T> extends Subscriber<T> {

  private connection: Subscription;

  constructor(destination: Subscriber<T>,
              private connectable: ConnectableObservable<T>) {
    super(destination);
  }

  protected _unsubscribe() {

    const { connectable } = this;
    if (!connectable) {
      this.connection = null;
      return;
    }

    this.connectable = null;
    const refCount = (<any> connectable)._refCount;
    if (refCount <= 0) {
      this.connection = null;
      return;
    }

    (<any> connectable)._refCount = refCount - 1;
    if (refCount > 1) {
      this.connection = null;
      return;
    }

    ///
    // Compare the local RefCountSubscriber's connection Subscription to the
    // connection Subscription on the shared ConnectableObservable. In cases
    // where the ConnectableObservable source synchronously emits values, and
    // the RefCountSubscriber's downstream Observers synchronously unsubscribe,
    // execution continues to here before the RefCountOperator has a chance to
    // supply the RefCountSubscriber with the shared connection Subscription.
    // For example:
    // ```
    // Observable.range(0, 10)
    //   .publish()
    //   .refCount()
    //   .take(5)
    //   .subscribe();
    // ```
    // In order to account for this case, RefCountSubscriber should only dispose
    // the ConnectableObservable's shared connection Subscription if the
    // connection Subscription exists, *and* either:
    //   a. RefCountSubscriber doesn't have a reference to the shared connection
    //      Subscription yet, or,
    //   b. RefCountSubscriber's connection Subscription reference is identical
    //      to the shared connection Subscription
    ///
    const { connection } = this;
    const sharedConnection = (<any> connectable)._connection;
    this.connection = null;

    if (sharedConnection && (!connection || sharedConnection === connection)) {
      sharedConnection.unsubscribe();
    }
  }
}