Plugins: Tasks

Another type of plugins gives us the ability to perform various actions during server/database startup process or enables us to perform actions periodically. For these instances we have introduced two interfaces and one abstract class.

public interface IStartupTask
{
void Execute(DocumentDatabase database);
}

public interface IServerStartupTask
{
void Execute(RavenDbServer server);
}

public abstract class AbstractBackgroundTask : IStartupTask
{
private static readonly ILog log = LogManager.GetCurrentClassLogger();

public DocumentDatabase Database { get; set; }

public void Execute(DocumentDatabase database)
{
	Database = database;
	Initialize();
	Task.Factory.StartNew(BackgroundTask, TaskCreationOptions.LongRunning);
}

protected virtual void Initialize()
{
}

int workCounter;
public void BackgroundTask()
{
	string name = GetType().Name;
	WorkContext context = Database.WorkContext;
	while (context.DoWork)
	{
		bool foundWork = false;
		try
		{
			foundWork = HandleWork();
		}
		catch (Exception e)
		{
			log.ErrorException("Failed to execute background task", e);
		}
		if (foundWork == false)
		{
			context.WaitForWork(TimeoutForNextWork(), ref workCounter, name);
		}
		else
		{
			context.UpdateFoundWork();
		}
	}
}

protected virtual TimeSpan TimeoutForNextWork()
{
	return TimeSpan.FromHours(1);
}

protected abstract bool HandleWork();
}

where:

• IStartupTask can be used to implement a task which will be started during database initialization.
• IServerStartupTask can be used to implement a task which will be started during server initialization.
• AbstractBackgroundTask is a base for all periodic tasks.

Example - Send email when server is starting

public class SendEmailWhenServerIsStartingTask : IServerStartupTask
{
public void Execute(RavenDbServer server)
{
	MailMessage message = new MailMessage("ravendb@myhost.com", "admin@myhost.com")
	{
		Subject = "RavenDB server started.",
		Body = "Start at: " + DateTime.Now.ToShortDateString()
	};

	using (SmtpClient smtpClient = new SmtpClient("mail.myhost.com"))
	{
		smtpClient.Send(message);
	}
}
}

Example - Perform a cleanup task during database initialization

public class CleanupWhenDatabaseIsStarting : IStartupTask
{
private const string SpecificDatabaseName = "Northwind";

public void Execute(DocumentDatabase database)
{
	if (database.Name != SpecificDatabaseName)
		return;

	using (CancellationTokenSource cts = new CancellationTokenSource())
	{
		bool stale;
		IEnumerable<string> queryResults = database.Queries.QueryDocumentIds(
			"Notifications/Temp",
			new IndexQuery(),
			CancellationTokenSource.CreateLinkedTokenSource(database.WorkContext.CancellationToken, cts.Token),
			out stale);

		foreach (string documentId in queryResults)
		{
			database.Documents.Delete(documentId, null, null);
		}
	}
}
}

Example - Perform a cleanup task every six hours

public class RemoveAllTemporaryNotificationsTask : AbstractBackgroundTask
{
protected override bool HandleWork()
{
	QueryResultWithIncludes queryResults = Database.Queries.Query("Notifications/Temp", new IndexQuery(), Database.WorkContext.CancellationToken);
	foreach (RavenJObject document in queryResults.Results)
	{
		string id = ((RavenJObject)document["@metadata"]).Value<string>("@id");
		Database.Documents.Delete(id, null, null);
	}

	return true;
}

protected override TimeSpan TimeoutForNextWork()
{
	return TimeSpan.FromHours(6);
}
}