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From: slY on 12 Jan 2010 12:08
I'm trying to write a piece of code that executes a task every n hours
(retrieving data via a Web Service).

I checked the web and I found this solution:

http://blog.apterainc.com/software/dotnet/scheduled-aspnet-task-aspnet-cron-jobs/

It seems to be very simple, but I have a couple of doubts.

Can somebody help me?

That are few simple functions used in the previously example:


Sub Application_Start(ByVal sender As Object, ByVal e As EventArgs)
RegisterCacheEntry()
End Sub


Private Sub RegisterCacheEntry()
If HttpContext.Current.Cache(CacheKey) Is Nothing Then
HttpContext.Current.Cache.Add(CacheKey, "WebScheduler", Nothing,
Caching.Cache.NoAbsoluteExpiration, _
TimeSpan.FromMinutes(1), CacheItemPriority.NotRemovable, _
New CacheItemRemovedCallback(AddressOf CacheItemRemovedCallback))
End If
End Sub


Private Sub CacheItemRemovedCallback(ByVal key As String, ByVal value
As Object, ByVal reason As CacheItemRemovedReason)
' Call To Do Scheduled Task
ScheduledTask.Task()

' Reset Timer
ResetTimer()
End Sub


Private Sub ResetTimer()
Dim Client As New Net.WebClient
Dim strReset As String = Client.DownloadString(ResetPage)
End Sub


Sub Application_BeginRequest(ByVal sender As Object, ByVal e As EventArgs)
If HttpContext.Current.Request.Url.ToString = ResetPage Then
RegisterCacheEntry()
End If
End Sub


Well, the author says that we use ResetPage to "make a call to dummy
page on your website".

But what is ResetPage? is it a real web page or can it be a fake one?

I think it should be a real one because the call
Client.DownloadString(ResetPage) will raise an exception in case of a
fake resource, right?

Can you image a different solution? (avoiding the implementation of a
Windows Service)


PS: a colleague of mine suggested me not to use Application_Start
because it is not so clear when this event is raised, do you agree?

Thank you very much,

slY
From: Patrice on 12 Jan 2010 12:29
Hello,

Don't you have a computer on which you could run a scheduled task ? ASP.NET
is just no intended to perform this. My personal preference is by far to
create a scheduled task on one of our server (or perhaps a service depending
what is does) and run this there...

IMO this ASP.NET solution could help if you have no server in house and want
for example to do that using a hosted website...

If you still want/need to go this route :

> But what is ResetPage? is it a real web page or can it be a fake one?

IMO just a real one that does nothing. The goal is to keep the site alive.

> Can you image a different solution? (avoiding the implementation of a
> Windows Service)

Why ? Is having this dummy page a problem ? To suggest another one it would
be betetr to first known what you don't like with the dummy page.

> Application_Start

It is raised when the application starts. Not sure what is the problem ? (a
confusion with Session_End ?) That said I agree that populating a cache
entry in Application_Start is perhaps not a general good idea. As soon as
you start to change how data are cached, it can begin to be a bad solution.
A more general approach is to put data in the cache when needed when d ata
are requested. This approach will work regardless of how data are cached.

--
Patrice



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