Component in Application Scope and cflock

Hi,
I have an CFC that I set in application scope in the
onApplicationStart method which contains some system parameters,
one of which is a flag saying whether the site is currently
"Online". I call a method on this CFC in the Application.cfc
"onRequest" method to see if the flag value has changed.
This method looks up a parameter set in the database that
says whether the site is "online" or "offline". If the site is
currently online, I want to only redo the query every 5 mins.
However if the site is offline, I want to check more frequently
(every 5 secs) as to whether the flag has changed back.
What I am not sure of, is whether I need to be using
<cflock> when I change from "online" to "offline"? There is
only a single instance of this object, but what happens if multiple
requests are calling the "isSiteOnline" method simultaneously? Is
this "safe"?
Some code snippets are attached to illustrate.
Any advice would be greatly appreciated.
Regards,
Andrew.

> 
No, in either situation.
Ask yourself... what would the ramifications be of two
requests hitting
that line of code "simultaneously"? The end result is that
both of them
are setting the variable to the same static value... so
that's what's going
to end up happening: variables.instance.cacheInterval is
going to be set to
300 (or 5) in each situation.
You could well with to lock a block of code which - if called
simultaneously via more than one request - could act on
shared storage
space (server, application or session data) differently and
incorrectly
than is intended.
eg:

<cfif not structKeyExists(application, isInitialised and
not
application.isInitialised>

<cfif allOK>
<cfset application.isInitialised = true>
<cfelse>
<cfset application.isInitialised = false>
</cfif>
</cfif>
So a sequence of events could be (say the user is hitting the
site with two
different browsers):
REQUEST1: application.isInitialised doesn't exist
REQUEST1: starts the init process
REQUEST2: application.isInitialised STILL doesn't exist
REQUEST2: starts the init process *again*
REQUEST1: sets the application.isInitialised value
REQUEST2: sets the application.isInitialised value
Obviously one does not want two request running the
initialisation code.
note this is a slightly contrived example, as if one has an
OnApplicationStart() method, then it will only run once, and
that's where
one would have the init code, but it demonstrates the issue.
Google "race condition". Those are the situations in which
one needs to
lock blocks of code.
Adam

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Edited by: navaneeth.j on Dec 17, 2009 4:04 AM

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Duke Snyder wrote:
> for some reason my cfc is not seeing any of the
variables set in
> application.cfm. Furthermore it does not see them when I
use application.cfc. I
> am running 6.1MX on iis5. Any info would be helpful.
>
> Thanks
>
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Component in Application Scope and cflock

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