Using the global.asa to schedule ASP code execution.
Have
you ever had some asp code that needed to execute every once in a while but, you just
didn't know how to do it.
There is a solution that doesn't involve running any scheduling or scripting software on
the server and is actually very easy to get working.
You see... there is a file called the "global.asa". Most ASP newbies
probably wonder what the heck it even is. The Global.asa file is event driven. It can
contain four event procedures: Application_OnStart,
Application_OnEnd, Session_OnStart,
and Session_OnEnd.
These event procedure stubs can contain script you want to be executed when the application starts or ends, or when
the session starts or ends.
For this article we will be focusing on the Session_OnStart event. It runs
when a user views a page on your Web application and it only runs once per
there session at the site.
With some tricky coding you can use this to schedule code to execute. At least around
the time you need it to, this won't be able to make it execute at exactly a certain time.
Here is the 1st example. It simply keeps track of how many visitors have been to your site
and after 100 it resets the count back to 0 and executes whatever code you need to run.
Obviously you'll need to adjust the "100" to whatever makes sense for the amount
of visitors your site receives.
Contents of the global.asa are below.
<SCRIPT LANGUAGE=VBScript RUNAT=Server>
Sub Application_OnStart
Application("SessionCount") = 0
End Sub
Sub Session_OnStart
Application.Lock
Application("SessionCount") = Application("SessionCount") + 1
Application.Unlock
If Application("SessionCount") > 100 Then
Application.Lock
Application("SessionCount") = 0
Application.Unlock
' Here you would put any code you need to run
' do not surround the code with <% %> tags
' For example you might run a database query that checks for expired accounts
End if
End Sub
</SCRIPT> |
Now lets say you want something to execute 4 times a
day. You can store the date & time in a text file and check it periodically. When the
date and time get to be more than 6 hours old the code will write the new date & time
to the text file and then execute the code you want to run. You could change the
"6" to whatever you want and therefore execute the code more or less often,
This is a pretty slick solution though it requires correct permissions to the text file
for reading & writing. If not you'll get an error.
In this example we are checking the text file every 15 visitors. You can adjust this
amount or remove the "check" completely so that it checks the file every time,
but why check the file every time when you have a very busy site ? That would just be a
waste of server resources ,but it is up to you how far you want to take this.
In this example you need to start the text file off with a valid date& time or else
you will get an error because the script will read in an empty value the 1st time.
EXAMPLE: put 6/30/99
6:58:45 PM in the 1st line of the text file.
You could add code to check for that and handle the error, but I didn't really care at the
time so I didn't do that. As long as there is a date there when it starts it will keep
working.
Contents of the global.asa are below.
<SCRIPT LANGUAGE=VBScript RUNAT=Server>
Sub Application_OnStart
Application("SessionCount") = 0
End Sub
Sub Session_OnStart
Application.Lock
Application("SessionCount") = Application("SessionCount") + 1
Application.Unlock
If Application("SessionCount") > 15 Then
Application.Lock
Application("SessionCount") = 0
Application.Unlock
Set ObjMyFile = CreateObject("Scripting.FileSystemObject")
Set OpenMyFile = ObjMyFile.OpenTextFile(Server.MapPath("last-update.txt"))
MyFileValue = OpenMyFile.ReadLine
OpenMyFile.Close
If DateDiff("h",MyFileValue,NOW) > 6 Then
' Here you would put
any code you need to run
' do not surround the code
with <% %> tags
' For example you might run a
database query that checks for expired accounts
Set WriteMyFile =
ObjMyFile.CreateTextFile(Server.MapPath("last-update.txt"))
WriteMyFile.WriteLine(NOW)
WriteMyFile.Close
End if
End If
End Sub
</SCRIPT> |
Please Note: There are many ways to
make this better and many different possible variations of what to check for before
executing the desired code. This article should get you started and give you some ideas.
Also remember that if the web is not set up to run as an application the
"global.asa" will not run. You'll need to make sure the web is an application.
Most Virtual Domains are by default, but sub webs usually are not.
For the sub webs to run the 'global.asa" they need to be an
application as the root usually is. In NT this is accomplished via the Internet Service
Manager under the properties of the sub web you want to make an application.
One Last Thing: Before you put any code in
your Global.asa to execute during events test it first in a regular ".asp" page.
If it doesn't run there it sure isn't going to run in your global.asa. Also make sure your
file paths are correct for the text file. Everything has to be perfect for this sort of
thing to work.
Good Luck
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