reactive/AsyncRx.NET/System.Reactive.Async.Linq/System/Reactive/Linq/Operators/SubscribeOn.cs

// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT License.
// See the LICENSE file in the project root for more information. 

using System.Reactive.Concurrency;
using System.Reactive.Disposables;

namespace System.Reactive.Linq
{
    public partial class AsyncObservable
    {
        public static IAsyncObservable<TSource> SubscribeOn<TSource>(this IAsyncObservable<TSource> source, IAsyncScheduler scheduler)
        {
            if (source == null)
                throw new ArgumentNullException(nameof(source));
            if (scheduler == null)
                throw new ArgumentNullException(nameof(scheduler));

            return SubscribeOn(source, scheduler, scheduler);
        }

        public static IAsyncObservable<TSource> SubscribeOn<TSource>(this IAsyncObservable<TSource> source, IAsyncScheduler subscribeScheduler, IAsyncScheduler disposeScheduler)
        {
            if (source == null)
                throw new ArgumentNullException(nameof(source));
            if (subscribeScheduler == null)
                throw new ArgumentNullException(nameof(subscribeScheduler));
            if (disposeScheduler == null)
                throw new ArgumentNullException(nameof(disposeScheduler));

            return Create(
                source,
                (subscribeScheduler, disposeScheduler),
                default(TSource),
                async (source, state, observer) =>
                {
                    var m = new SingleAssignmentAsyncDisposable();
                    var d = new SerialAsyncDisposable();

                    await d.AssignAsync(m).ConfigureAwait(false);

                    var scheduled = await state.subscribeScheduler.ScheduleAsync(async ct =>
                    {
                        var subscription = await source.SubscribeSafeAsync(observer).RendezVous(state.subscribeScheduler, ct);

                        var scheduledDispose = AsyncDisposable.Create(async () =>
                        {
                            await state.disposeScheduler.ScheduleAsync(async _ =>
                            {
                                await subscription.DisposeAsync().RendezVous(state.disposeScheduler, ct);
                            }).ConfigureAwait(false);
                        });

                        await d.AssignAsync(scheduledDispose).RendezVous(state.subscribeScheduler, ct);
                    }).ConfigureAwait(false);

                    await m.AssignAsync(scheduled).ConfigureAwait(false);

                    return d;
                });
        }
    }
}