Preloading some data at application startup as fast as possible

One way to do this is to launch a Task at application startup as soon as possible (the DI is configured). The only hard part is to make DI available in the prewarm functionality.

The following implementation is based on this article.

/// <summary>
/// Credit: https://anduin.aiursoft.com/post/2020/10/14/fire-and-forget-in-aspnet-core-with-dependency-alive
/// </summary>
public class FireAndForgetService
{
	private readonly ILogger<FireAndForgetService> _logger;
	private readonly IServiceScopeFactory _scopeFactory;

	public FireAndForgetService(
		ILogger<FireAndForgetService> logger,
		IServiceScopeFactory scopeFactory)
	{
		_logger = logger;
		_scopeFactory = scopeFactory;
	}

	public void Fire<T>(Action<T> bullet, Action<Exception> handler = null)
	{
		_logger.LogInformation("Fired a new action.");
		Task.Run(() =>
		{
			using var scope = _scopeFactory.CreateScope();
			var dependency = scope.ServiceProvider.GetRequiredService<T>();
			try
			{
				bullet(dependency);
			}
			catch (Exception e)
			{
				_logger.LogError(e, "Fire and forget crashed!");
				handler?.Invoke(e);
			}
			finally
			{
				dependency = default;
			}
		});
	}

	public void FireAsync<T>(Func<T, Task> bullet, Action<Exception> handler = null)
	{
		_logger.LogInformation("Fired a new async action.");
		Task.Run(async () =>
		{
			using var scope = _scopeFactory.CreateScope();
			var dependency = scope.ServiceProvider.GetRequiredService<T>();
			try
			{
				await bullet(dependency);
			}
			catch (Exception e)
			{
				_logger.LogError(e, "Cannon crashed!");
				handler?.Invoke(e);
			}
			finally
			{
				dependency = default;
			}
		});
	}
}

// this goes in Startup.ConfigureServices
services.AddSingleton<FireAndForgetService>();

// this goes in Program.cs

private static void PreWarmCache(IServiceProvider services, NLog.Logger _logger)
{
	try
	{
		var cannon = services.GetRequiredService<FireAndForgetService>();

		cannon.FireAsync<IListOfValuesProviderService>(async (lovProvider) =>
		{
			_ = await lovProvider.GetAll<Employee>(default);
		});
	}
	catch (Exception exc)
	{
		// log error
	}
	
}

public async static Task Main(string[] args)
{
	try
	{
		var host = CreateHostBuilder(args).Build();

		using (var scope = host.Services.CreateScope())
		{
			await host.MigrateDatabaseAsync<ApplicationDbContext>();

			var services = scope.ServiceProvider;

			PreWarmCache(services, _logger);
		}

		await host.RunAsync();
	}
	catch (Exception ex)
	{
		// log error
		throw;
	}
}

Note that cannon.FireAsync is not awaited and it does not block the application startup.

posted almost 3 years ago

CC BY-SA 4.0

Alexei‭

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