Adding ConnectableAsyncObservable.

AsyncRx.NET/System.Reactive.Async/System/Reactive/Subjects/ConnectableAsyncObservable.cs

@@ -0,0 +1,73 @@
+// 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.Linq;
+using System.Threading;
+using System.Threading.Tasks;
+
+namespace System.Reactive.Subjects
+{
+    internal sealed class ConnectableAsyncObservable<TSource, TResult> : IConnectableAsyncObservable<TResult>
+    {
+        private readonly IAsyncSubject<TSource, TResult> subject;
+        private readonly IAsyncObservable<TSource> source;
+        private readonly AsyncLock gate = new AsyncLock();
+
+        private Connection connection;
+
+        public ConnectableAsyncObservable(IAsyncObservable<TSource> source, IAsyncSubject<TSource, TResult> subject)
+        {
+            this.subject = subject;
+            this.source = source.AsAsyncObservable();
+        }
+
+        public async Task<IAsyncDisposable> ConnectAsync()
+        {
+            using (await gate.LockAsync().ConfigureAwait(false))
+            {
+                if (connection == null)
+                {
+                    var subscription = await source.SubscribeAsync(subject).ConfigureAwait(false);
+                    connection = new Connection(this, subscription);
+                }
+
+                return connection;
+            }
+        }
+
+        private sealed class Connection : IAsyncDisposable
+        {
+            private readonly ConnectableAsyncObservable<TSource, TResult> parent;
+            private IAsyncDisposable subscription;
+
+            public Connection(ConnectableAsyncObservable<TSource, TResult> parent, IAsyncDisposable subscription)
+            {
+                this.parent = parent;
+                this.subscription = subscription;
+            }
+
+            public async Task DisposeAsync()
+            {
+                using (await parent.gate.LockAsync().ConfigureAwait(false))
+                {
+                    if (subscription != null)
+                    {
+                        await subscription.DisposeAsync().ConfigureAwait(false);
+                        subscription = null;
+
+                        parent.connection = null;
+                    }
+                }
+            }
+        }
+
+        public Task<IAsyncDisposable> SubscribeAsync(IAsyncObserver<TResult> observer)
+        {
+            if (observer == null)
+                throw new ArgumentNullException(nameof(observer));
+
+            return subject.SubscribeAsync(observer);
+        }
+    }
+}