EF Core multithreading issue

Question

I have a simple project which has not update/delete and I insert using dapper library. I use ef core just for fetching data (mostly asNoTracking). Note that

I use the default scoped DbContext
I use a full async ef repository

Startup.cs

services.AddDbContext<MyContext>(options =>
            {
                options.UseSqlServer(_configuration.GetConnectionString("DefaultConnection"),
                sqlServerOptionsAction: sqlOptions =>
                
                   {
                    sqlOptions.EnableRetryOnFailure(
                    maxRetryCount: 10,
                    maxRetryDelay: TimeSpan.FromSeconds(30),
                    errorNumbersToAdd: null);
                });
            },

This is one of the methods in my generic repository

public async Task<List<TDto>> GetAsNoTrackingAsync<TDto>(Expression<Func<T, bool>> predicate)
        {
            return await Context.Set<T>()
                         .AsNoTracking()
                         .Where(x => !x.IsDeleted)
                         .Where(predicate)
                         .OrderByDescending(e => e.RTime)
                         .ToListAsync();
        }

and how I use it:

var result = await _repository.GetAsNoTrackingAsync<TDto>(e => e.Id == id);

but unfortunately I encounter with the below multithreading issue rarely which is strange for me.

A second operation was started on this context before a previous operation completed. This is usually caused by different threads concurrently using the same instance of DbContext. For more information on how to avoid threading issues with DbContext, see https://go.microsoft.com/fwlink/?linkid=2097913.

I have searched a lot for this issue, but found no solution except making the DbContext as transient (which I think it is not a solution).

It is not 100% percent reproduciblem but I sometimes I could do so by multiple requesting the request (e.g. clicking on F5 button twice quickly)

Any solution is appreciated.

Please show the context class and a typical method that causes this exception. It's not *only* lifetime scope that can lead to this issue. — Gert Arnold, Oct 17 '21 at 15:04
@Kourosh, Are you sure you are correctly using async await, Might be missing some await and it's executing multiple thing at same time on context. — Anirudha Gupta, Oct 17 '21 at 15:38
Please provide enough code so others can better understand or reproduce the problem. — Community, Oct 17 '21 at 16:31
Entity Framework is not thread-safe. Each content can only be used by one thread. https://stackoverflow.com/questions/4455634/entity-framework-thread-safety — Enigmativity, Oct 18 '21 at 00:06
@anirudhagupta Yes, I have reviewed the codes multiple times for missing `await` keyword — Kourosh, Oct 18 '21 at 07:41
The problem is 2 calls are executing at the same time on same instance. If you can use some kind of lock(obj) it might help. — Anirudha Gupta, Oct 18 '21 at 09:01
@enigmativity Yes, I see. I use async/await methods fully for ef-related tasks and as my dbcontext is configured to be scoped, my question is what is the best pattern for using ef dbcontext? — Kourosh, Oct 18 '21 at 11:41
@enigmativity services refers to `Startup.cs > ConfigureServices(IServiceCollection services)` method — Kourosh, Oct 18 '21 at 11:41

EF Core multithreading issue

0 Answers0