Initial implementation of Timeout.

Ix.NET/Source/System.Interactive.Async/System/Linq/Operators/Timeout.cs

@@ -0,0 +1,101 @@
+// 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.Collections.Generic;
+using System.Diagnostics;
+using System.Threading;
+using System.Threading.Tasks;
+
+namespace System.Linq
+{
+    public static partial class AsyncEnumerableEx
+    {
+        public static IAsyncEnumerable<TSource> Timeout<TSource>(this IAsyncEnumerable<TSource> source, TimeSpan timeout)
+        {
+            if (source == null)
+                throw new ArgumentNullException(nameof(source));
+
+            var num = (long)timeout.TotalMilliseconds;
+            if (num < -1L || num > int.MaxValue)
+                throw new ArgumentOutOfRangeException(nameof(timeout));
+
+            return new TimeoutAsyncIterator<TSource>(source, timeout);
+        }
+
+        private sealed class TimeoutAsyncIterator<TSource> : AsyncIterator<TSource>
+        {
+            private readonly IAsyncEnumerable<TSource> source;
+            private readonly TimeSpan timeout;
+
+            private IAsyncEnumerator<TSource> enumerator;
+
+            public TimeoutAsyncIterator(IAsyncEnumerable<TSource> source, TimeSpan timeout)
+            {
+                Debug.Assert(source != null);
+
+                this.source = source;
+                this.timeout = timeout;
+            }
+
+            public override AsyncIterator<TSource> Clone()
+            {
+                return new TimeoutAsyncIterator<TSource>(source, timeout);
+            }
+
+            public override async Task DisposeAsync()
+            {
+                if (enumerator != null)
+                {
+                    await enumerator.DisposeAsync().ConfigureAwait(false);
+                    enumerator = null;
+                }
+
+                await base.DisposeAsync().ConfigureAwait(false);
+            }
+
+            protected override async Task<bool> MoveNextCore()
+            {
+                switch (state)
+                {
+                    case AsyncIteratorState.Allocated:
+                        enumerator = source.GetAsyncEnumerator();
+
+                        state = AsyncIteratorState.Iterating;
+                        goto case AsyncIteratorState.Iterating;
+
+                    case AsyncIteratorState.Iterating:
+                        var moveNext = enumerator.MoveNextAsync();
+
+                        if (!moveNext.IsCompleted)
+                        {
+                            using (var delayCts = new CancellationTokenSource())
+                            {
+                                var delay = Task.Delay(timeout, delayCts.Token);
+
+                                var winner = await Task.WhenAny(moveNext, delay).ConfigureAwait(false);
+
+                                if (winner == delay)
+                                {
+                                    throw new TimeoutException();
+                                }
+
+                                delayCts.Cancel();
+                            }
+                        }
+
+                        if (await moveNext.ConfigureAwait(false))
+                        {
+                            current = enumerator.Current;
+                            return true;
+                        }
+
+                        break;
+                }
+
+                await DisposeAsync().ConfigureAwait(false);
+                return false;
+            }
+        }
+    }
+}