dbContext is Disposed in a Time Hosted Service

I'm trying to get my TimeHostedService with a DBContext to work but I always get the error: Cannot access a disposed context instance. So here is my Code:

First of all, I have my DoWork Method inside my Time Hosted Service. Because the class that I call (IEasyConficService) is scoped and the TimeHosted Service is singleton, I have to implement it with the scope.ServiceProvider. I think, this is so far fine.

private void DoWork(object? state)
{
    using var scope = _serviceScopeFactory.CreateScope();
    var easyConfigService = scope.ServiceProvider.GetRequiredService<IEasyConfigService>();
    easyConfigService.ExecuteUnfinishedEasyConfigs();
}

Now my function ExecuteUnfinishedEasyConfigs is collecting all the unfinished Gateways that I have from the Database. And then give it to the Method 'TryExecuteEasyConfig'.

public async Task ExecuteUnfinishedEasyConfigs()
{
    var gateways = _context.Gateways.Include(g => g.Machine)
        .Where(g => g.EasyConfigStatus == EasyConfigStatus.OnGoing)
        .Include(g => g.Machine)
        .ThenInclude(m => m.MachineType)
        .ToList();
    await Parallel.ForEachAsync(gateways, async (gateway, _) => await TryExecuteEasyConfig(gateway));
}

This works so far, because the _context is set in the constructor of the class with DI.

public class EasyConfigService : IEasyConfigService {
    private readonly SuncarContext _context;
    
    public EasyConfigService(SuncarContext context)
    {
        _context = context;
    }
}

But inside the TryExecuteEasyConfig method, which is also in the class EasyConfigService, I get the disposed Error from above, if I try call _context.SaveChangesAsync()

private async Task TryExecuteEasyConfig(Gateway gateway)
{
    // Do some Stuff
    await _context.SaveChangesAsync();
}

I do not know, why I can first take some Information out of the DBContext and afterwards the SaveChangesAsync() is failing. Why is the _context now disposed?

First I thought, it is because I do a Parallel.FoarEachAsync but it also happend, if I do a normal foreach. Is there any way to use a DBContext safely inside a TimeHostedService?

Edit 15.06.2023 11:12

The normal foreach is looking like:

foreach (var gateway in gateways)
{
    await TryExecuteEasyConfig(gateway);
}

Edit 15.06.2023 11:16

The SuncarContext is added as following:

services.AddDbContext<SuncarContext>(options =>
    options.UseNpgsql(Configuration.GetConnectionString("PostgresConnection"),
        sqlOption =>
        {
            sqlOption.EnableRetryOnFailure(
                5,
                TimeSpan.FromSeconds(5),
                null);
        }
    ));

Edit 15.06.2023 11.21

The Time Hosted Service is Using the StartAsync Method, where I use a Timer, that is calling a DoWork Method.

using System;
using System.Threading;
using System.Threading.Tasks;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Hosting;
using Microsoft.Extensions.Logging;

namespace Backend.BusinessLayer.Services.Interfaces;

public class EasyConfigExecutor : IHostedService, IDisposable {
    private readonly ILogger<EasyConfigExecutor> _logger;
    private Timer? _timer;
    private readonly IServiceScopeFactory _serviceScopeFactory;

    public EasyConfigExecutor(ILogger<EasyConfigExecutor> logger, IServiceScopeFactory serviceScopeFactory)
    {
        _logger = logger;
        _serviceScopeFactory = serviceScopeFactory;
    }

    public Task StartAsync(CancellationToken stoppingToken)
    {
        _timer = new Timer(DoWork, null, TimeSpan.Zero, TimeSpan.FromSeconds(30));

        return Task.CompletedTask;
    }

    private void DoWork(object? state)
    {
        using var scope = _serviceScopeFactory.CreateScope();
        var easyConfigService = scope.ServiceProvider.GetService<IEasyConfigService>() ?? throw new ArgumentNullException();
        easyConfigService.ExecuteUnfinishedEasyConfigs();
    }

    public Task StopAsync(CancellationToken stoppingToken)
    {
        _timer?.Change(Timeout.Infinite, 0);

        return Task.CompletedTask;
    }

    public void Dispose()
    {
        _timer?.Dispose();
    }
}

Edit 15.06.2023 14.22 - Conclusion

The Answer of Dai definitely works. Thanks for your support.

After looking through the Internet, I found also a good article from Microsoft, how to use timed asynchronous background task in c#. That's the way I'm using it now. Probably this will help some other people: Micosoft Timed asynchronous background Task