Entity Framework Core: different threads using the same instance of DbContext - multithreading

Question

The application was developed on ASP NET Core 3. To log user actions, I decided to use a single method in the Project class. Faced the problem of using one singleton dbContext from different threads.
Startup.cs
public void ConfigureServices(IServiceCollection services)
{
string connection = Configuration.GetConnectionString("ConnectionDB");
services.AddDbContext<DataBaseContext>(options => options.UseSqlServer(connection), ServiceLifetime.Transient, ServiceLifetime.Singleton);
services.AddSingleton<Project>();
}
Project.cs
public async Task AddUserLog(string action, string message, int userId)
{
try
{
UserLog userLog = new UserLog()
{
Action = action,
Message = message,
UserId = userId
Datepoint = DateTime.Now
};
_dbContext.UserLog.Add(userLog);
await _dbContext.SaveChangesAsync();
}
catch (Exception ex)
{
await AddSystemLog("Project", "AddUserLog", ex.Message);
}
}
SchemeController.cs
public class SchemeController : ControllerBase
{
private readonly Project _project;
public SchemeController(Project project)
{
_project = project;
}
[Authorize(Policy = "AdvancedControl")]
[HttpPost("[action]")]
public async Task SomeMethode()
{
for (int i = 0; i < 10; i++)
{
await _project.AddUserLog("Text", "Message", 42);
}
}
}
Already at the second iteration of the loop, I catch an exception in the AddUserLog method:
"A second operation started on this context before a previous operation completed. This is usually caused by different threads using the same instance of DbContext."
I suggest several solutions:
Add the log to the buffer table and then save it to the database by timer. But this is not the best way out;
Block the method while it is being saved to the database.
But I don’t like any of the options.
Please tell me the correct approach in solving this issue.

Answer 1

So, you trying to use shared resource (singleton Project class) to perform parallel operations (save UserLogs) while your shared resource implementation is not thread-safe (exceptions raised).
You have at lease three ways to solve this:
Do not use shared resource: register Project per scope instead of singletone;
Do not perform operations in parallel: seems hard to achieve because you making webapp and you can't force user(s) to wait
Refactor your resource to be thread-safe: add locks/mutexes/buffering... inside Project
There is no one "correct" way - all 3 are correct. Choose one you like (or combine several).
Usually using scoped dbcontext is recommended (because connections are pooled), but it's the creator of app who should decide.