DbContext multithreading issue with ASP.NET Core middleware

Question

I have a middleware registered once. It contains InvokeAsync.

I noticed that sometimes I get errors due to multithreaded access to the DbContext which I'm not doing. The problem I found that somehow my middleware is called twice per request. And since there is DbContext, it causes multithreading issue.

Simplified code:

public class UserIdMiddleware
{
    private readonly RequestDelegate _next;
    private readonly IUserService _userService;

    public UserIdMiddleware(RequestDelegate next, IUserService userService)
    {
        _next = next;
        _userService = userService;
    }

    public async Task InvokeAsync(HttpContext context) // called twice
    {
        int? userId = await _userService.GetUserIdByUid(decodedToken.Uid);
        await _next(context);
    }
}

app.UseMiddleware<UserIdMiddleware>();

It was probably my mistake, I forgot that I may have other threads on the client when debugging it, so I thought it would be one request. But The problem is with the wrong DI in middleware.

Why does it work this way? How to avoid it?

Answer 1

You could try as below follow this document:

public UserIdMiddleware(RequestDelegate next )
    {
        _next = next;
        
    }

    public async Task InvokeAsync(HttpContext context,IUserService userService) 
    {
        int? userId = await userService.GetUserIdByUid(decodedToken.Uid);
        await _next(context);
    }

when it comes to why you get into InvokeAsync method twice,you could check this document