ObjectDisposedException in Blazor server rendered app

[JamesNK]

Is there an existing issue for this?

• I have searched the existing issues

Describe the bug

The error below is showing up in our app's error telemetry. It has happened 100 times in the last 7 days.

System.ObjectDisposedException: Cannot access a disposed object.
at Microsoft.AspNetCore.Components.RenderTree.ArrayBuilder`1.GrowBuffer(Int32 desiredCapacity)
   at Microsoft.AspNetCore.Components.RenderTree.RenderTreeDiffBuilder.InsertNewFrame(DiffContext& diffContext, Int32 newFrameIndex)
   at Microsoft.AspNetCore.Components.RenderTree.RenderTreeDiffBuilder.AppendDiffEntriesForRange(DiffContext& diffContext, Int32 oldStartIndex, Int32 oldEndIndexExcl, Int32 newStartIndex, Int32 newEndIndexExcl)
   at Microsoft.AspNetCore.Components.RenderTree.RenderTreeDiffBuilder.ComputeDiff(Renderer renderer, RenderBatchBuilder batchBuilder, Int32 componentId, ArrayRange`1 oldTree, ArrayRange`1 newTree)
   at Microsoft.AspNetCore.Components.Rendering.ComponentState.RenderIntoBatch(RenderBatchBuilder batchBuilder, RenderFragment renderFragment, Exception& renderFragmentException)
   at Microsoft.AspNetCore.Components.RenderTree.Renderer.ProcessRenderQueue()

I'm guessing it happens in rare situations where something in Blazor (the circuit?) is aborted at the same time as rendering.

Expected Behavior

If Blazor component is aborted while it is still running then I'd expect abort-related errors to be caught and ignored.

Steps To Reproduce

I don't have a repo. Just error info and counts from telemetry.

Exceptions (if any)

No response

.NET Version

No response

Anything else?

No response

[javiercn]

I think this might be happening if something calls dispose in the middle of a batch being processed.

There is some locking stuff that we added as part of #52724 which might have changed the semantics of how this works.

Ultimately it might be the case that Dispose is being called in the middle of us executing a batch (from outside of the sync context maybe?)

We should at least check https://github.com/dotnet/aspnetcore/blob/main/src/Components/Components/src/RenderTree/Renderer.cs to point out there is a render in progress.

[javiercn]

@JamesNK isn't there anything else on the call stack?

This has a check on ProcessPendingRender
(https://github.com/dotnet/aspnetcore/blob/main/src/Components/Components/src/RenderTree/Renderer.cs#L787-L791)

The other thing I can think of is and OnAfterRender queuing things after the circuit has disconnected. https://github.com/dotnet/aspnetcore/blob/main/src/Components/Components/src/RenderTree/Renderer.cs#L869

[JamesNK]

I don’t think we have a complete stack trace, but I’ll check tomorrow and see if more is available.

The app might be running on .net 8. Has the check been added since then?

[javiercn]

@JamesNK I struggle a bit to see how this can be happening (but its obviously happening), the key is to understand the sequence of events that cause this to happen. Are there any logs that we could capture along the exception? (Debug logs) that would help us clarify what's going on.

[JamesNK]

I don’t think we have a complete stack trace, but I’ll check tomorrow and see if more is available.

The previous stack trace is all that's available. We just record the exception details when an error happens. We don't have logs of what lead up to it.

I assume the error happens because the array builder is disposed after ProcessRenderQueue() has been called. I'd fix this kind of thing by not logging ObjectDisposedException and OperationCanceledException if the renderer has been disposed.