Hold a separate kernel instance for each notebook to avoid interference

Api/Api.csproj

@@ -7,6 +7,7 @@
 
   <ItemGroup>
     <PackageReference Include="Microsoft.Azure.Functions.Extensions" Version="1.1.0" />
+    <PackageReference Include="Microsoft.Extensions.Caching.Memory" Version="3.1.9" />
     <PackageReference Include="Microsoft.NET.Sdk.Functions" Version="3.0.3" />
     <PackageReference Include="Microsoft.DotNet.Interactive.CSharp" Version="1.0.0-beta.20426.1" />
     <PackageReference Include="FSharp.Compiler.Private.Scripting" Version="11.0.0-beta.20428.1" />

Api/KernelFunctions.cs

@@ -21,10 +21,10 @@ namespace blazoract.Api
 {
     public class KernelFunction
     {
-        private CompositeKernel _kernel;
-        public KernelFunction(CompositeKernel kernel)
+        private KernelStore _kernels;
+        public KernelFunction(KernelStore kernels)
         {
-            this._kernel = kernel;
+            _kernels = kernels;
         }
 
         [FunctionName("RunCode")]
@@ -33,9 +33,9 @@ public async Task<IActionResult> RunCode(
             ILogger log)
         {
             string requestBody = await new StreamReader(req.Body).ReadToEndAsync();
-            var cell = JsonConvert.DeserializeObject<ExecuteRequest>(requestBody);
-
-            var request = await _kernel.SendAsync(new SubmitCode(cell.Input), new CancellationToken());
+            var executeRequest = JsonConvert.DeserializeObject<ExecuteRequest>(requestBody);
+            var kernel = _kernels.GetKernelForNotebook(executeRequest.NotebookId);
+            var request = await kernel.SendAsync(new SubmitCode(executeRequest.Code), CancellationToken.None);
             var result = new ExecuteResult();
             request.KernelEvents.Subscribe(x =>
             {
@@ -62,7 +62,8 @@ public async Task<IActionResult> GetCompletions(
             string requestBody = await new StreamReader(req.Body).ReadToEndAsync();
             var completionRequest = JsonConvert.DeserializeObject<GetCompletionsRequest>(requestBody);
 
-            var request = await _kernel.SendAsync(new RequestCompletions(completionRequest.Code, new LinePosition(completionRequest.LineNumber - 1, completionRequest.Column - 1)));
+            var kernel = _kernels.GetKernelForNotebook(completionRequest.NotebookId);
+            var request = await kernel.SendAsync(new RequestCompletions(completionRequest.Code, new LinePosition(completionRequest.LineNumber - 1, completionRequest.Column - 1)));
             var result = Array.Empty<Suggestion>();
             request.KernelEvents.Subscribe(x =>
             {

Api/KernelStore.cs

@@ -0,0 +1,42 @@
+using Microsoft.Azure.Functions.Extensions.DependencyInjection;
+using Microsoft.DotNet.Interactive.CSharp;
+using Microsoft.DotNet.Interactive;
+using System.Collections.Concurrent;
+using Microsoft.Extensions.Caching.Memory;
+using System;
+
+[assembly: FunctionsStartup(typeof(blazoract.Api.Startup))]
+
+namespace blazoract.Api
+{
+    // To avoid interference across notebooks, we need a separate kernel instance per notebook.
+    // Set up a cache in memory that holds a certain maximum number of instances, and evicts
+    // entries if they become idle for longer than a certain period.
+
+    public class KernelStore
+    {
+        const int MaxEntries = 1024;
+        const int MaxIdleMinutes = 15;
+
+        private MemoryCache _kernelsCache = new MemoryCache(new MemoryCacheOptions
+        {
+            SizeLimit = MaxEntries
+        });
+
+        private ConcurrentDictionary<string, CompositeKernel> _kernels
+            = new ConcurrentDictionary<string, CompositeKernel>();
+
+        public CompositeKernel GetKernelForNotebook(string notebookId)
+        {
+            return _kernelsCache.GetOrCreate(notebookId, entry =>
+            {
+                entry.SetSlidingExpiration(TimeSpan.FromMinutes(MaxIdleMinutes));
+                entry.Size = 1;
+                return new CompositeKernel()
+                {
+                    new CSharpKernel().UseDefaultFormatting().UseDotNetVariableSharing()
+                };
+            });
+        }
+    }
+}

Api/Startup.cs

@@ -1,7 +1,5 @@
 using Microsoft.Azure.Functions.Extensions.DependencyInjection;
 using Microsoft.Extensions.DependencyInjection;
-using Microsoft.DotNet.Interactive.CSharp;
-using Microsoft.DotNet.Interactive;
 
 [assembly: FunctionsStartup(typeof(blazoract.Api.Startup))]
 
@@ -11,9 +9,7 @@ public class Startup : FunctionsStartup
     {
         public override void Configure(IFunctionsHostBuilder builder)
         {
-            builder.Services.AddSingleton<CompositeKernel>(new CompositeKernel() {
-                new CSharpKernel().UseDefaultFormatting().UseDotNetVariableSharing()
-            });
+            builder.Services.AddSingleton<KernelStore>();
         }
     }
-}
+}

Client/Data/NotebookService.cs

@@ -30,7 +30,7 @@ public NotebookService(ILocalStorageService storage, HttpClient http)
             var initialContent = new List<Cell>();
             for (var i = 0; i < 100; i++)
             {
-                initialContent.Add(new Cell($"{i} * {i}", i));
+                initialContent.Add(new Cell(id, $"{i} * {i}", i));
             }
             notebook.Cells = initialContent;
             _storage.SetItemAsync("_default_notebook", notebook);
@@ -57,7 +57,7 @@ public async Task<string> CreateNewNotebook()
             var id = Guid.NewGuid().ToString("N");
             var title = "New notebook";
             var notebook = new Notebook(title, id);
-            notebook.Cells = new List<Cell>() { new Cell("", 0) };
+            notebook.Cells = new List<Cell>() { new Cell(id, "// Type your code here", 0) };
             await _storage.SetItemAsync(id, notebook);
 
             var notebooks = await _storage.GetItemAsync<List<string>>("blazoract-notebooks") ?? new List<string>();
@@ -71,7 +71,7 @@ public async Task<string> CreateNewNotebook()
         public async Task<Notebook> AddCell(string id, string content, CellType type, int position)
         {
             var notebook = await GetById(id);
-            notebook.Cells.Insert(position, new Cell(content, position, type));
+            notebook.Cells.Insert(position, new Cell(id, content, position, type));
             await _storage.SetItemAsync(id, notebook);
             OnChange.Invoke();
             return notebook;

Client/Shared/CodeCell.razor

@@ -62,7 +62,7 @@
         try
         {
             isEvaluating = true;
-            var request = new ExecuteRequest(cell.Content);
+            var request = new ExecuteRequest(cell.NotebookId, cell.Content);
             var response = await Http.PostAsJsonAsync("api/code/run", request);
             result = await response.Content.ReadFromJsonAsync<ExecuteResult>();
         }
@@ -76,6 +76,7 @@
     {
         var response = await Http.PostAsJsonAsync("api/code/completions", new GetCompletionsRequest
         {
+            NotebookId = cell.NotebookId,
             Code = value,
             Column = position.Column,
             LineNumber = position.LineNumber

Shared/Cell.cs

@@ -4,12 +4,16 @@ namespace blazoract.Shared
 {
     public class Cell
     {
-        public Cell(string content, int position, CellType type = CellType.Code)
+        public Cell(string notebookId, string content, int position, CellType type = CellType.Code)
         {
+            NotebookId = notebookId;
             Content = content;
             Position = position;
             Type = type;
         }
+
+        public string NotebookId { get; set; }
+
         public string Content { get; set; }
 
         public CellType Type { get; set; }

Shared/ExecuteRequest.cs

@@ -4,10 +4,14 @@ namespace blazoract.Shared
 {
     public class ExecuteRequest
     {
-        public ExecuteRequest(string input)
+        public ExecuteRequest(string notebookId, string code)
         {
-            Input = input;
+            NotebookId = notebookId;
+            Code = code;
         }
-        public string Input { get; set; }
+
+        public string NotebookId { get; set; }
+
+        public string Code { get; set; }
     }
 }

Shared/GetCompletionsRequest.cs

@@ -2,6 +2,7 @@
 {
     public class GetCompletionsRequest
     {
+        public string NotebookId { get; set; }
         public string Code { get; set; }
         public int LineNumber { get; set; }
         public int Column { get; set; }