Adding SubscribeOn.

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

@@ -0,0 +1,49 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the Apache 2.0 License.
+// See the LICENSE file in the project root for more information. 
+
+using System.Reactive.Concurrency;
+using System.Reactive.Disposables;
+
+namespace System.Reactive.Linq
+{
+    // REVIEW: Consider more fine-grained control over subscribe and dispose schedulers.
+
+    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 Create<TSource>(async observer =>
+            {
+                var m = new SingleAssignmentAsyncDisposable();
+                var d = new SerialAsyncDisposable();
+
+                await d.AssignAsync(m).ConfigureAwait(false);
+
+                var scheduled = await scheduler.ScheduleAsync(async ct =>
+                {
+                    var subscription = await source.SubscribeSafeAsync(observer).RendezVous(scheduler);
+
+                    var scheduledDispose = AsyncDisposable.Create(async () =>
+                    {
+                        await scheduler.ScheduleAsync(async _ =>
+                        {
+                            await subscription.DisposeAsync().RendezVous(scheduler);
+                        }).ConfigureAwait(false);
+                    });
+
+                    await d.AssignAsync(scheduledDispose).RendezVous(scheduler);
+                }).ConfigureAwait(false);
+
+                await m.AssignAsync(scheduled).ConfigureAwait(false);
+
+                return d;
+            });
+        }
+    }
+}