Using the ASP.NET Cache as a Scheduler
UPDATED
By using the ASP.NET cache, it is very easy to create a simple scheduling mechanism, for example, one that fires an event every X minutes. I once wrote a simple module to do just this, here is its code. It is up to you to enhance it to your needs!
public class SchedulerModule: IHttpModule
{
#region Public constructor
public SchedulerModule()
{
this.Enabled = true;
this.Interval = TimeSpan.FromMinutes(1); //fires every minute
this.FirstTime = true;
}
#endregion
#region Public properties
public Boolean Enabled
{
get;
set;
}
public TimeSpan Interval
{
get;
set;
}
public Boolean FirstTime
{
get;
private set;
}
#endregion
#region Public events
public event EventHandler Tick;
public event EventHandler Start;
public event EventHandler Stop;
#endregion
#region Protected methods
protected void StartScheduler()
{
CacheItemRemovedCallback callback = null;
HttpContext context = HttpContext.Current;
callback = delegate(String key, Object value, CacheItemRemovedReason reason)
{
if (reason == CacheItemRemovedReason.Expired)
{
if (this.Enabled == true)
{
this.StartRunning(callback, context);
}
if (this.FirstTime == true)
{
this.FirstTime = false;
this.OnStart(EventArgs.Empty);
}
this.OnTick(EventArgs.Empty);
if (this.Enabled == false)
{
this.OnStop(EventArgs.Empty);
}
}
};
this.StartRunning(callback, context);
}
protected void StartRunning(CacheItemRemovedCallback callback, HttpContext context)
{
context.Cache.Add(Guid.NewGuid().ToString(), Guid.NewGuid().ToString(), null, DateTime.Now + this.Interval, Cache.NoSlidingExpiration, CacheItemPriority.NotRemovable, callback);
}
#endregion
#region Protected virtual methods
protected virtual void OnStart(EventArgs e)
{
EventHandler handler = this.Start;
if (handler != null)
{
handler(this, EventArgs.Empty);
}
}
protected virtual void OnStop(EventArgs e)
{
EventHandler handler = this.Stop;
if (handler != null)
{
handler(this, EventArgs.Empty);
}
}
protected virtual void OnTick(EventArgs e)
{
EventHandler handler = this.Tick;
if (handler != null)
{
handler(this, EventArgs.Empty);
}
}
#endregion
#region IHttpModule Members
public void Dispose()
{
this.Enabled = false;
}
public void Init(HttpApplication context)
{
this.StartScheduler();
}
#endregion
}
It exposes two properties:
- Enabled: if the scheduler is active
- Interval: the firing interval
As for the installation, you just have to reference it on your web.config:
There's two ways in which you can use it: by manually wiring an event, maybe on Application_Start, or by writing special methods, use one or the other, not both!
protected void Application_Start(Object sender, EventArgs e)
{
//Note: you do not have to do this if you use the following methods!
//SchedulerModule schedulerModule = HttpContext.Current.ApplicationInstance.Modules.OfType<SchedulerModule>().Single();
SchedulerModule schedulerModule = this.Modules.OfType<SchedulerModule>().Single();
//Set the firing interval
schedulerModule.Interval = TimeSpan.FromMinutes(5);
schedulerModule.Start += this.Scheduler_Start;
schedulerModule.Stop += this.Scheduler_Stop;
schedulerModule.Tick += this.Scheduler_Tick;
}
protected void Scheduler_Start(Object sender, EventArgs e)
{
}
protected void Scheduler_Stop(Object sender, EventArgs e)
{
}
protected void Scheduler_Tick(Object sender, EventArgs e)
{
}
