Blazor Index Out of Range Exception

[cyberjaws]

Describe the bug

Exception thrown: 'System.IndexOutOfRangeException' in System.Private.CoreLib.dll
System.IndexOutOfRangeException: Index was outside the bounds of the array.
at System.Collections.Generic.Dictionary`2.TryInsert(TKey key, TValue value, InsertionBehavior behavior)

I have a periodic task that runs at 1Hz and components that get their data and update their state call StateHasChanged() at that frequency.

To Reproduce

1. Using this version of ASP.NET Core: Blazor 0.7.0
2. Run this code:

            _updateTimer = new Timer((state) =>
            {
                try
                {
                    Updated();
                }
                catch(Exception ext)
                {
                    System.Diagnostics.Trace.WriteLine(ext.ToString());
                }
            }, null, TimeSpan.FromSeconds(1), TimeSpan.FromSeconds(1));

3. With these arguments:
   Blazor Components that register for this event call StateHasChanged() when appropriate.
4. See error:

Exception thrown: 'System.IndexOutOfRangeException' in System.Private.CoreLib.dll
System.IndexOutOfRangeException: Index was outside the bounds of the array.
   at System.Collections.Generic.Dictionary`2.TryInsert(TKey key, TValue value, InsertionBehavior behavior)
   at Microsoft.AspNetCore.Blazor.Rendering.Renderer.AssignEventHandlerId(RenderTreeFrame& frame)
   at Microsoft.AspNetCore.Blazor.RenderTree.RenderTreeDiffBuilder.AppendDiffEntriesForAttributeFrame(DiffContext& diffContext, Int32 oldFrameIndex, Int32 newFrameIndex)
   at Microsoft.AspNetCore.Blazor.RenderTree.RenderTreeDiffBuilder.AppendAttributeDiffEntriesForRange(DiffContext& diffContext, Int32 oldStartIndex, Int32 oldEndIndexExcl, Int32 newStartIndex, Int32 newEndIndexExcl)
   at Microsoft.AspNetCore.Blazor.RenderTree.RenderTreeDiffBuilder.AppendDiffEntriesForFramesWithSameSequence(DiffContext& diffContext, Int32 oldFrameIndex, Int32 newFrameIndex)
   at Microsoft.AspNetCore.Blazor.RenderTree.RenderTreeDiffBuilder.AppendDiffEntriesForRange(DiffContext& diffContext, Int32 oldStartIndex, Int32 oldEndIndexExcl, Int32 newStartIndex, Int32 newEndIndexExcl)
   at Microsoft.AspNetCore.Blazor.RenderTree.RenderTreeDiffBuilder.ComputeDiff(Renderer renderer, RenderBatchBuilder batchBuilder, Int32 componentId, ArrayRange`1 oldTree, ArrayRange`1 newTree)
   at Microsoft.AspNetCore.Blazor.Rendering.ComponentState.RenderIntoBatch(RenderBatchBuilder batchBuilder, RenderFragment renderFragment)
   at Microsoft.AspNetCore.Blazor.Rendering.Renderer.RenderInExistingBatch(RenderQueueEntry renderQueueEntry)
   at Microsoft.AspNetCore.Blazor.Rendering.Renderer.ProcessRenderQueue()
   at Microsoft.AspNetCore.Blazor.Rendering.Renderer.AddToRenderQueue(Int32 componentId, RenderFragment renderFragment)
   at Microsoft.AspNetCore.Blazor.Server.Circuits.CircuitSynchronizationContext.ExecuteSynchronously(TaskCompletionSource`1 completion, SendOrPostCallback d, Object state)
   at Microsoft.AspNetCore.Blazor.Server.Circuits.CircuitSynchronizationContext.Post(SendOrPostCallback d, Object state)
   at NG.Blazor.Client.Components.Settings.<OnAfterRender>b__10_0() in C:\compile\BlazorEcdis\NG.Blazor.Client\Components\Settings.cshtml:line 32
   at NG.Blazor.Client.DataService.<.ctor>b__7_0(Object state) in C:\compile\BlazorEcdis\NG.Blazor.Client\DataService.cs:line 31

Expected behavior

Dictionary can be added to.

Screenshots

N/A

Additional context

Likely this could be addressed by changing the Dictionary that houses the _eventBindings (and _componentStateById?) to a Concurrent Dictionary here:
https://github.com/aspnet/AspNetCore/blob/436b5461ad0337aac90089aa7ccb61dd875808e4/src/Components/src/Microsoft.AspNetCore.Components/Rendering/Renderer.cs

[mkArtakMSFT]

Thanks for contacting us, @cyberjaws.
@SteveSandersonMS can you please look into this? Thanks!

[springy76]

This bug still exists in Razor Components 3.0 preview 2 (end of Jan2019).

RemoveEventHandlerIds runs asynchronously (called from thread pool) and corrupts the _eventBindings dictionary by modifiying it without any locking mechanism.

I've seen multiple threads doing RemoveEventHandlerIds in parallel for the very same Renderer instance and also RemoveEventHandlerIds run in parallel with building a new render tree diff.

I'm using no timers but just some OnInitAsync and OnParameterSetAsync overrides .

[DNF-SaS]

Also experiencing this issue here using Razor Components from ASP.NET Core 3.0 Preview 2.

[cyberjaws]

I ported my app to Core 3.0 Preview 2. I was pleased to see cross threading exceptions from calling StateHasChanged() from a Threading.Timer's callback. (They been addressed using the newly supplied Invoke/InvokeAsync methods in the component's base. Thank you for addressing that!) Unfortunately I too still see this bug.

[cyberjaws]

For those tracking this ticket, it looks like some work has been done for the next release that should resolve this issue. Appears that the calls to the Renderer are going to be passed through an Invoker to ensure there won't be cross threaded access to the Dictionaries.

[cyberjaws]

Alas, I am still getting exceptions with Preview 3.

[cyberjaws]

Even with a try catch in Preview 3, the Signal R socket ends up disconnecting when this error occurs.

[JohanDonne]

Having the same problem, including SignalR disconnect. This is pretty disruptive...
edit: using razor components.

[springy76]

While I did not see the IndexOutOfRangeException since preview3, the display freeze followed by a SignalR timeout after 30s in browser still happens far too often.

I made a test project for simulating this: https://github.com/springy76/RazorComponentsProblems/blob/problem/ConnectionDiesWhenUsingAsyncOperations/WebApp/Components/Pages/Index.razor

Sometimes you only have to click some of the 12 buttons, sometimes you have to alternate for a minute. But sooner or later the display will freeze ("loading" text will not disappear, all buttons without function) and 30s later the browser will log connection timeout to debug console.

Even after having disabled "just my code", and enabling every .net exception and every managed debugging assistant in exception settings, I did not see neither an exception in debugger nor deadlocked threads in thread-list. I wonder if anyone can narrow this down?

[cyberjaws]

@springy76 Thanks for posting. These could be related, however I would recommend creating another ticket for the disconnect and then link them.