Blazor WebAssembly Monitor Threading exception

Question

I'm currently working on a .NET Standard 2.1 Blazor WebAssembly hosted application.

My application structure looks like this:

BlazorApp.Client (error occures here)
BlazorApp.Server

I use Serilog with the Elasticsearch sink in my BlazorApp.Client project. It works fine, but when I enable Selflog on Serilog and debug, I get the following error in my browser console:

SelfLog.Enable(msg => Debug.WriteLine(msg));

Elasticsearch.Net.UnexpectedElasticsearchClientException: Cannot wait on monitors on this runtime. ---> System.Threading.SynchronizationLockException: Cannot wait on monitors on this runtime.

at (wrapper managed-to-native) System.Threading.Monitor.Monitor_wait(object,int)

at System.Threading.Monitor.ObjWait (System.Boolean exitContext, System.Int32 millisecondsTimeout, System.Object obj) <0x36c60c8 + 0x00046> in :0

at System.Threading.Monitor.Wait (System.Object obj, System.Int32 millisecondsTimeout, System.Boolean exitContext) <0x36c5de8 + 0x00022> in :0

It seems to be an issue in the current Blazor WASm release: https://github.com/dotnet/aspnetcore/issues/22400

Cannot Wait on monitors Does anyone know, how to possibly get rid of this error in Blazor WebAssembly Client?

I think the current MONO runtime on WASM only supports a single thread. — Peter Morris
– Peter Morris, Commented Aug 13, 2020 at 15:29
For SO-users struggling with the same error message, you can consult stackoverflow.com/questions/78684132/…, also answered by Henk Holterman. If that question/answer helps you, please give an upvote to Holterman on this question below. — Ioannes Arkhipov
– Ioannes Arkhipov, Commented Jun 28, 2024 at 20:16

Henk Holterman · Accepted Answer · 2025-05-19 08:28:43Z

6

You cannot 'get rid of' that error in Blazor WebAssembly. WebAssembly code is (for the time being) single-threaded so executing System.Threading.Monitor.Wait(something); would be a guaranteed deadlock.

The framework correctly signals to you that this code is not suitable for WebAssembly.

You will have to get rid of of any code that needs to Wait(),
and that usually appears as lock(x) { ... } .

edited May 19 at 8:28

answered Aug 13, 2020 at 17:14

Henk Holterman

276k33 gold badges353 silver badges540 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

Maor Solomonov · Accepted Answer · 2025-05-19 07:32:02Z

0

Adding to Henk's answer:

You cannot 'get rid of' that error in Blazor WebAssembly. WebAssembly code is (for the time being) single-threaded so executing System.Threading.Monitor.Wait(something); would be a guaranteed deadlock.

The framework correctly signals to you that this code is not suitable for WebAssembly.

You will have to get rid of of any code that needs to Wait() (that usually appears as lock(x) { ... } ).

There are places you can invoke asynchronous methods. Those are your components' Async methods. The most popular of them is OnAfterRenderAsync

Example:

protected override async Task OnAfterRenderAsync(bool firstRender)
{
    await JsRuntime.InvokeVoidAsync("console.log", "This message will show up in the console");
}

answered May 19 at 7:32

Maor Solomonov

142 bronze badges

2 Comments

Henk Holterman May 19 at 7:41

Yes, but async is not the same as threading. Javascript demands that all I/O is async. But do not use .Wait() or .Result on a Task, always await.

Maor Solomonov May 19 at 8:24

You're absolutely right. I never worked with 'Elasticsearch' or 'Serilog', but I experienced the same error message while trying to await a sync method. So I thought to add this answer for future readers that search on the error message.

Collectives™ on Stack Overflow

Blazor WebAssembly Monitor Threading exception

2 Answers 2

Comments

2 Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

Comments

2 Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related