Background Jobs in C# — A Practical Guide for .NET Developers

public class CleanupService : BackgroundService
{
    protected override async Task ExecuteAsync(CancellationToken stoppingToken)
    {
        var timer = new PeriodicTimer(TimeSpan.FromHours(1));

        while (await timer.WaitForNextTickAsync(stoppingToken))
        {
            await DeleteExpiredSessionsAsync();
        }
    }
}

builder.Services.AddHostedService<CleanupService>();

[HTTP Request] → writes to Channel → [BackgroundService] → processes items

// In your API — enqueue the work
await _channelWriter.WriteAsync(new EmailMessage(user.Email));

// In your BackgroundService — process the work
await foreach (var msg in _channelReader.ReadAllAsync(ct))
    await SendEmailAsync(msg);

// Fire & forget
BackgroundJob.Enqueue<IEmailService>(s => s.SendWelcomeEmail(userId));

// Delayed
BackgroundJob.Schedule<IEmailService>(s => s.SendReminder(userId), TimeSpan.FromDays(3));

// Recurring
RecurringJob.AddOrUpdate<IReportService>("nightly-report", s => s.Generate(), Cron.Daily());

// Run at 9am on the 1st of every month
q.AddTrigger(opts => opts
    .ForJob(jobKey)
    .WithCronSchedule("0 0 9 1 * ?"));

Do jobs need to survive a restart?
│
├── No  ──→  BackgroundService or Channels
│
└── Yes ──→  Need complex scheduling?
             │
             ├── Yes ──→  Quartz.NET
             │
             └── No  ──→  Running on Azure / AWS?
                          │
                          ├── Yes ──→  Service Bus / SQS
                          │
                          └── No  ──→  Hangfire

// Pass the token to every async call
await DoWorkAsync(stoppingToken);

// Check before acting
if (user.WelcomeEmailSentAt.HasValue) return; // already done

await SendEmailAsync(user);
user.WelcomeEmailSentAt = DateTimeOffset.UtcNow;
await db.SaveChangesAsync();

_logger.LogInformation("Processing job {JobId} for user {UserId}", jobId, userId);