Adding n-ary Zip.

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

@@ -0,0 +1,137 @@
+// 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.Linq;
+using System.Reactive.Disposables;
+using System.Threading;
+using System.Threading.Tasks;
+
+namespace System.Reactive.Linq
+{
+    partial class AsyncObservable
+    {
+        public static IAsyncObservable<IList<TSource>> Zip<TSource>(IEnumerable<IAsyncObservable<TSource>> sources) => Zip(sources.ToArray());
+
+        public static IAsyncObservable<IList<TSource>> Zip<TSource>(params IAsyncObservable<TSource>[] sources)
+        {
+            if (sources == null)
+                throw new ArgumentNullException(nameof(sources));
+
+            return Create<IList<TSource>>(async observer =>
+            {
+                var count = sources.Length;
+
+                var observers = AsyncObserver.Zip(observer, count);
+
+                var tasks = new Task<IAsyncDisposable>[count];
+
+                for (var i = 0; i < count; i++)
+                {
+                    tasks[i] = sources[i].SubscribeAsync(observers[i]);
+                }
+
+                await Task.WhenAll(tasks).ConfigureAwait(false);
+
+                return StableCompositeAsyncDisposable.Create(tasks.Select(t => t.Result));
+            });
+        }
+    }
+
+    partial class AsyncObserver
+    {
+        public static IAsyncObserver<TSource>[] Zip<TSource>(IAsyncObserver<IList<TSource>> observer, int count)
+        {
+            if (observer == null)
+                throw new ArgumentNullException(nameof(observer));
+            if (count < 0)
+                throw new ArgumentOutOfRangeException(nameof(count));
+
+            var gate = new AsyncLock();
+
+            var queues = new Queue<TSource>[count];
+            var isDone = new bool[count];
+            var res = new IAsyncObserver<TSource>[count];
+
+            IAsyncObserver<TSource> CreateObserver(int index) =>
+                Create<TSource>(
+                    async x =>
+                    {
+                        using (await gate.LockAsync().ConfigureAwait(false))
+                        {
+                            queues[index].Enqueue(x);
+
+                            if (queues.All(queue => queue.Count > 0))
+                            {
+                                var list = new TSource[count];
+
+                                for (var i = 0; i < count; i++)
+                                {
+                                    list[i] = queues[i].Dequeue();
+                                }
+
+                                await observer.OnNextAsync(list).ConfigureAwait(false);
+                            }
+                            else
+                            {
+                                var allDone = true;
+
+                                for (var i = 0; i < count; i++)
+                                {
+                                    if (i != index && !isDone[i])
+                                    {
+                                        allDone = false;
+                                        break;
+                                    }
+                                }
+
+                                if (allDone)
+                                {
+                                    await observer.OnCompletedAsync().ConfigureAwait(false);
+                                }
+                            }
+                        }
+                    },
+                    async ex =>
+                    {
+                        using (await gate.LockAsync().ConfigureAwait(false))
+                        {
+                            await observer.OnErrorAsync(ex).ConfigureAwait(false);
+                        }
+                    },
+                    async () =>
+                    {
+                        using (await gate.LockAsync().ConfigureAwait(false))
+                        {
+                            isDone[index] = true;
+
+                            var allDone = true;
+
+                            for (var i = 0; i < count; i++)
+                            {
+                                if (!isDone[i])
+                                {
+                                    allDone = false;
+                                    break;
+                                }
+                            }
+
+                            if (allDone)
+                            {
+                                await observer.OnCompletedAsync().ConfigureAwait(false);
+                            }
+                        }
+                    }
+                );
+
+            for (var i = 0; i < count; i++)
+            {
+                queues[i] = new Queue<TSource>();
+                res[i] = CreateObserver(i);
+            }
+
+            return res;
+        }
+    }
+}