Application Variables by Charles Carroll

There are two kinds of data that your program can manipulate that can be used to "remember" data:

Session data
which is "attached" to a person browsing your site. If the same page is accessed by 12 different users each user may have totally different session values.

Application data
which is attached to the webserver and is the same no matter which user is accessing the site.

Application values are visible to every user. But since, unlike session data, any web page could change the application's data there is a potential concurrency issue. The lock and unlock method of the application object eliminate concurrency issues. Once an application is locked, no other updates to the application object can occur until the unlock is executed.

One use for an application variable would be to store variables most scripts on a site needed to access or even HTML cached from databases like in
The Worlds Fastest Listbox Example @
http://www.learnasp.com/freebook/asp/speedappdata.aspx

One example I use to illustrate the conceptual use for each type of data would be a website that simulated a casino. Player's individual winnings make perfect sense to maintain in session variables. However, the total number of players at each "virtual table" (blackjack, roulette, etc.) would be application data as the would be the same regardless of an individual player's status.

Here is a file called appblackjacklook.asp that displays how many people are at the table.

   filename=/learn/test/appblackjacklook.asp

<Test Script Below>

<% 
response.write "Over at the BlackJack Table<br>"
response.write "There are " & application("bjplayers") & " players there!<br>"
%>

Here is a file called appblackjackarrive.asp that could be included in any script where someone arrived at the blackjack table!

   filename=/learn/test/appblackjackarrive.asp

<Test Script Below>

<% 
response.write "Welcome to the BlackJack Table<br>"
application.lock
application("bjplayers")=application("bjplayers")+1
application.unlock
response.write "There are " & application("bjplayers") & " players here!<br>"
%>

Here is a file called appblackjackleave.asp that could be included in any script where someone left the blackjack table!

   filename=/learn/test/appblackjackleave.asp

<Test Script Below>

<% 
response.write "Thanks for playing BlackJack!<br>"
application.lock
application("bjplayers")=application("bjplayers")-1
IF application("bjplayers")<0 THEN
    application("bjplayers")=0
END IF
application.unlock
response.write "There are " & application("bjplayers") & " players still at the table!<br>"
%>

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