From f1f0dec8d672b5071a4293dbe12e93ca75809118 Mon Sep 17 00:00:00 2001
From: Jens Chr <jc@calwin.dk>
Date: Wed, 20 Nov 2019 09:52:42 +0100
Subject: [PATCH 1/2] Add test for support of large enumerables

---
 .../System/Linq/Operators/ToObservable.cs     | 28 +++++++++++++++++++
 1 file changed, 28 insertions(+)

diff --git a/Ix.NET/Source/System.Linq.Async.Tests/System/Linq/Operators/ToObservable.cs b/Ix.NET/Source/System.Linq.Async.Tests/System/Linq/Operators/ToObservable.cs
index ba6f5cc2be..796b22132a 100644
--- a/Ix.NET/Source/System.Linq.Async.Tests/System/Linq/Operators/ToObservable.cs
+++ b/Ix.NET/Source/System.Linq.Async.Tests/System/Linq/Operators/ToObservable.cs
@@ -269,6 +269,34 @@ public void ToObservable_DesNotCallMoveNextAgainWhenSubscriptionIsDisposed()
             Assert.Equal(1, moveNextCount);
             Assert.False(fail);
         }
+        
+        [Fact]
+        public void ToObservable_SupportsLargeEnumerable()
+        {
+            using var evt = new ManualResetEvent(false);
+
+            var fail = false;
+
+            var xs = AsyncEnumerable.Range(0, 10000).ToObservable();
+            xs.Subscribe(new MyObserver<int>(
+                x =>
+                {
+                    // ok
+                },
+                ex =>
+                {
+                    fail = true;
+                    evt.Set();
+                },
+                () =>
+                {
+                    evt.Set();
+                }
+            ));
+
+            evt.WaitOne();
+            Assert.False(fail);
+        }
 
         private sealed class MyObserver<T> : IObserver<T>
         {

From 09033f5190119163aa187038cefb2b47cf2a68e5 Mon Sep 17 00:00:00 2001
From: Jens Chr <jc@calwin.dk>
Date: Wed, 20 Nov 2019 09:53:00 +0100
Subject: [PATCH 2/2] Replace tail recursion with while loop

---
 .../System/Linq/Operators/ToObservable.cs     | 53 ++++++++++---------
 1 file changed, 29 insertions(+), 24 deletions(-)

diff --git a/Ix.NET/Source/System.Linq.Async/System/Linq/Operators/ToObservable.cs b/Ix.NET/Source/System.Linq.Async/System/Linq/Operators/ToObservable.cs
index f2e74d95bd..90f4face95 100644
--- a/Ix.NET/Source/System.Linq.Async/System/Linq/Operators/ToObservable.cs
+++ b/Ix.NET/Source/System.Linq.Async/System/Linq/Operators/ToObservable.cs
@@ -32,39 +32,44 @@ public IDisposable Subscribe(IObserver<T> observer)
 
                 async void Core()
                 {
-                    bool hasNext;
-                    try
+                    while (true)
                     {
-                        hasNext = await e.MoveNextAsync().ConfigureAwait(false);
-                    }
-                    catch (Exception ex)
-                    {
-                        if (!ctd.Token.IsCancellationRequested)
+                        bool hasNext;
+                        try
                         {
-                            observer.OnError(ex);
-                            await e.DisposeAsync().ConfigureAwait(false);
+                            hasNext = await e.MoveNextAsync().ConfigureAwait(false);
                         }
+                        catch (Exception ex)
+                        {
+                            if (!ctd.Token.IsCancellationRequested)
+                            {
+                                observer.OnError(ex);
+                                await e.DisposeAsync().ConfigureAwait(false);
+                            }
 
-                        return;
-                    }
+                            return;
+                        }
 
-                    if (hasNext)
-                    {
-                        observer.OnNext(e.Current);
+                        if (hasNext)
+                        {
+                            observer.OnNext(e.Current);
+
+                            if (!ctd.Token.IsCancellationRequested)
+                            {
+                                continue;
+                            }
 
-                        if (!ctd.Token.IsCancellationRequested)
+                            // In case cancellation is requested, this could only have happened
+                            // by disposing the returned composite disposable (see below).
+                            // In that case, e will be disposed too, so there is no need to dispose e here.
+                        }
+                        else
                         {
-                            Core();
+                            observer.OnCompleted();
+                            await e.DisposeAsync().ConfigureAwait(false);
                         }
 
-                        // In case cancellation is requested, this could only have happened
-                        // by disposing the returned composite disposable (see below).
-                        // In that case, e will be disposed too, so there is no need to dispose e here.
-                    }
-                    else
-                    {
-                        observer.OnCompleted();
-                        await e.DisposeAsync().ConfigureAwait(false);
+                        break;
                     }
                 }