Adding Sample.

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

@@ -0,0 +1,162 @@
+// 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;
+using System.Threading;
+using System.Threading.Tasks;
+
+namespace System.Reactive.Linq
+{
+    partial class AsyncObservable
+    {
+        public static IAsyncObservable<TSource> Sample<TSource, TSample>(this IAsyncObservable<TSource> source, IAsyncObservable<TSample> sampler)
+        {
+            if (source == null)
+                throw new ArgumentNullException(nameof(source));
+            if (sampler == null)
+                throw new ArgumentNullException(nameof(sampler));
+
+            return Create<TSource>(async observer =>
+            {
+                var (sourceSink, samplerSink) = AsyncObserver.Sample<TSource, TSample>(observer);
+
+                var sourceSubscription = await source.SubscribeSafeAsync(sourceSink).ConfigureAwait(false);
+                var samplerSubscription = await sampler.SubscribeSafeAsync(samplerSink).ConfigureAwait(false);
+
+                return StableCompositeAsyncDisposable.Create(sourceSubscription, samplerSubscription);
+            });
+        }
+
+        public static IAsyncObservable<TSource> Sample<TSource>(this IAsyncObservable<TSource> source, TimeSpan interval)
+        {
+            if (source == null)
+                throw new ArgumentNullException(nameof(source));
+
+            return Create<TSource>(async observer =>
+            {
+                var (sourceSink, sampler) = await AsyncObserver.Sample(observer, interval).ConfigureAwait(false);
+
+                var sourceSubscription = await source.SubscribeSafeAsync(sourceSink).ConfigureAwait(false);
+
+                return StableCompositeAsyncDisposable.Create(sourceSubscription, sampler);
+            });
+        }
+
+        public static IAsyncObservable<TSource> Sample<TSource>(this IAsyncObservable<TSource> source, TimeSpan interval, IAsyncScheduler scheduler)
+        {
+            if (source == null)
+                throw new ArgumentNullException(nameof(source));
+            if (scheduler == null)
+                throw new ArgumentNullException(nameof(scheduler));
+
+            return Create<TSource>(async observer =>
+            {
+                var (sourceSink, sampler) = await AsyncObserver.Sample(observer, interval, scheduler).ConfigureAwait(false);
+
+                var sourceSubscription = await source.SubscribeSafeAsync(sourceSink).ConfigureAwait(false);
+
+                return StableCompositeAsyncDisposable.Create(sourceSubscription, sampler);
+            });
+        }
+    }
+
+    partial class AsyncObserver
+    {
+        public static (IAsyncObserver<TSource>, IAsyncObserver<TSample>) Sample<TSource, TSample>(IAsyncObserver<TSource> observer)
+        {
+            if (observer == null)
+                throw new ArgumentNullException(nameof(observer));
+
+            var gate = new AsyncLock();
+
+            var hasValue = false;
+            var value = default(TSource);
+            var atEnd = false;
+
+            async Task OnSampleAsync()
+            {
+                using (await gate.LockAsync().ConfigureAwait(false))
+                {
+                    if (hasValue)
+                    {
+                        hasValue = false;
+                        await observer.OnNextAsync(value).ConfigureAwait(false);
+                    }
+
+                    if (atEnd)
+                    {
+                        await observer.OnCompletedAsync().ConfigureAwait(false);
+                    }
+                }
+            }
+
+            return
+                (
+                    Create<TSource>(
+                        async x =>
+                        {
+                            using (await gate.LockAsync().ConfigureAwait(false))
+                            {
+                                hasValue = true;
+                                value = x;
+                            }
+                        },
+                        async ex =>
+                        {
+                            using (await gate.LockAsync().ConfigureAwait(false))
+                            {
+                                await observer.OnErrorAsync(ex).ConfigureAwait(false);
+                            }
+                        },
+                        async () =>
+                        {
+                            using (await gate.LockAsync().ConfigureAwait(false))
+                            {
+                                atEnd = true;
+                            }
+                        }
+                    ),
+                    Create<TSample>(
+                        _ => OnSampleAsync(),
+                        async ex =>
+                        {
+                            using (await gate.LockAsync().ConfigureAwait(false))
+                            {
+                                await observer.OnErrorAsync(ex).ConfigureAwait(false);
+                            }
+                        },
+                        OnSampleAsync
+                    )
+                );
+        }
+
+        public static Task<(IAsyncObserver<TSource>, IAsyncDisposable)> Sample<TSource>(IAsyncObserver<TSource> observer, TimeSpan interval)
+        {
+            if (observer == null)
+                throw new ArgumentNullException(nameof(observer));
+
+            return Sample(observer, interval, TaskPoolAsyncScheduler.Default);
+        }
+
+        public static Task<(IAsyncObserver<TSource>, IAsyncDisposable)> Sample<TSource>(IAsyncObserver<TSource> observer, TimeSpan interval, IAsyncScheduler scheduler)
+        {
+            if (observer == null)
+                throw new ArgumentNullException(nameof(observer));
+            if (scheduler == null)
+                throw new ArgumentNullException(nameof(scheduler));
+
+            async Task<(IAsyncObserver<TSource>, IAsyncDisposable)> CoreAsync()
+            {
+                var (sink, timer) = Sample<TSource, long>(observer);
+
+                var sampler = await Interval(timer, interval, scheduler).ConfigureAwait(false);
+
+                return (sink, sampler);
+            }
+
+            return CoreAsync();
+        }
+    }
+}