import { Operator } from '../Operator';
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import { Subscriber } from '../Subscriber';
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import { Observable } from '../Observable';
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import { SubscribeOnObservable } from '../observable/SubscribeOnObservable';
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import { MonoTypeOperatorFunction, SchedulerLike, TeardownLogic } from '../types';
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/**
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* Asynchronously subscribes Observers to this Observable on the specified {@link SchedulerLike}.
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*
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* With `subscribeOn` you can decide what type of scheduler a specific Observable will be using when it is subscribed to.
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*
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* Schedulers control the speed and order of emissions to observers from an Observable stream.
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*
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* 
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*
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* ## Example
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* Given the following code:
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* ```javascript
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* import { of, merge } from 'rxjs';
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*
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* const a = of(1, 2, 3, 4);
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* const b = of(5, 6, 7, 8, 9);
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* merge(a, b).subscribe(console.log);
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* ```
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*
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* Both Observable `a` and `b` will emit their values directly and synchronously once they are subscribed to.
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* This will result in the output of `1 2 3 4 5 6 7 8 9`.
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*
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* But if we instead us the `subscribeOn` operator declaring that we want to use the {@link asyncScheduler} for values emited by Observable `a`:
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* ```javascript
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* import { of, merge, asyncScheduler } from 'rxjs';
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* import { subscribeOn } from 'rxjs/operators';
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*
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* const a = of(1, 2, 3, 4).pipe(subscribeOn(asyncScheduler));
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* const b = of(5, 6, 7, 8, 9);
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* merge(a, b).subscribe(console.log);
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* ```
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*
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* The output will instead be `5 6 7 8 9 1 2 3 4`.
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* The reason for this is that Observable `b` emits its values directly and synchronously like before
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* but the emissions from `a` are scheduled on the event loop because we are now using the {@link asyncScheduler} for that specific Observable.
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*
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* @param {SchedulerLike} scheduler - The {@link SchedulerLike} to perform subscription actions on.
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* @return {Observable<T>} The source Observable modified so that its subscriptions happen on the specified {@link SchedulerLike}.
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.
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* @method subscribeOn
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* @owner Observable
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*/
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export function subscribeOn<T>(scheduler: SchedulerLike, delay: number = 0): MonoTypeOperatorFunction<T> {
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return function subscribeOnOperatorFunction(source: Observable<T>): Observable<T> {
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return source.lift(new SubscribeOnOperator<T>(scheduler, delay));
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};
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}
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class SubscribeOnOperator<T> implements Operator<T, T> {
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constructor(private scheduler: SchedulerLike,
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private delay: number) {
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}
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call(subscriber: Subscriber<T>, source: any): TeardownLogic {
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return new SubscribeOnObservable<T>(
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source, this.delay, this.scheduler
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).subscribe(subscriber);
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}
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}
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