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EVENTS
The ASP platform allows developers to create Web Applications.
In fulfillment of real software requirements, ASP allows
event-triggered actions to be taken, which are defined in
a global.asa file. The global.asa file resides in the
Global directory, defined as a config option , and may
define the following actions:
Action Event
------ ------
Script_OnStart * Beginning of Script execution
Script_OnEnd * End of Script execution
Application_OnStart Beginning of Application
Application_OnEnd End of Application
Session_OnStart Beginning of user Session.
Session_OnEnd End of user Session.
* These are API extensions that are not portable, but were
added because they are incredibly useful
These actions must be defined in the $Global/global.asa file
as subroutines, for example:
sub Session_OnStart {
$Application->{$Session->SessionID()} = started;
}
Sessions are easy to understand. When visiting a page in a
web application, each user has one unique $Session. This
session expires, after which the user will have a new
$Session upon revisiting.
A web application starts when the user visits a page in that
application, and has a new $Session created. Right before
the first $Session is created, the $Application is created.
When the last user $Session expires, that $Application
expires also.
Script_OnStart & Script_OnEnd
The script events are used to run any code for all scripts
in an application defined by a global.asa. Often, you would
like to run the same code for every script, which you would
otherwise have to add by hand, or add with a file include,
but with these events, just add your code to the global.asa,
and it will be run.
There is one caveat. Code in Script_OnEnd is not guaranteed
to be run when the user hits a STOP button, since the program
execution ends immediately at this event. To always run critical
code, use the API extension:
$Server->RegisterCleanup()
Application_OnStart
This event marks the beginning of an ASP application, and
is run just before the Session_OnStart of the first Session
of an application. This event is useful to load up
$Application with data that will be used in all user sessions.
Application_OnEnd
The end of the application is marked by this event, which
is run after the last user session has timed out for a
given ASP application.
Session_OnStart
Triggered by the beginning of a user's session, Session_OnStart
gets run before the user's executing script, and if the same
session recently timed out, after the session's triggered Session_OnEnd.
The Session_OnStart is particularly useful for caching database data,
and avoids having the caching handled by clumsy code inserted into
each script being executed.
Session_OnEnd
Triggered by a user session ending, Session_OnEnd can be useful
for cleaning up and analyzing user data accumulated during a session.
Sessions end when the session timeout expires, and the StateManager
performs session cleanup. The timing of the Session_OnEnd does not
occur immediately after the session times out, but when the first
script runs after the session expires, and the StateManager allows
for that session to be cleaned up.
So on a busy site with default SessionTimeout (20 minutes) and
StateManager (10 times) settings, the Session_OnEnd for a particular
session should be run near 22 minutes past the last activity that Session saw.
A site infrequently visited will only have the Session_OnEnd run
when a subsequent visit occurs, and theoretically the last session
of an application ever run will never have its Session_OnEnd run.
Thus I would not put anything mission-critical in the Session_OnEnd,
just stuff that would be nice to run whenever it gets run.
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