Whopps...good catch....
However, you still get a race condition where multiple threads can
initialize the code. If you exit the read lock with a pre-chosen path to
initialize, then multiple threads can decide to initialize and will simply
wait their turn in the queue before initializing.
Am I missing something else? (Highly likely!)
An exclusive lock isn't optimal, so what is the solution? Maybe the second
body needs to do another check wrapped inside the EXCLUSIVE lock to make
sure it still is not defined? That case would seem to catch any of the
threads that slipped past, right?
-Dustin
-----Original Message-----
From: BOROVOY Noam [mailto:[EMAIL PROTECTED]]
Sent: Monday, August 28, 2000 10:30 AM
To: [EMAIL PROTECTED]
Subject: RE: No more need for cflock!!
Careful,
Can't do that - see below:
----------
From: Dustin Breese [SMTP:[EMAIL PROTECTED]]
Sent: Monday, 28 August 2000 18:09
To: [EMAIL PROTECTED]; Fusebox
Subject: RE: No more need for cflock!!
Steve,
Only suggestion I would make here is to put the initialization code
inside
the CFLOCK -- it keeps multiple threads from running the same init
logic.
Probably a low possibility, but it could definitely happen in a
high-transaction environment. Just in case the init logic is a
big-hitter!
For example:
<cflock name="#application.applicationname#" timeout="60"
type="readonly">
<cfif not isdefined("application.requestapp")>
<!--- DO THE INIT LOGIC WITHIN THE LOCK, NOT WITHOUT
--->
Here you need to have a write lock NOT a read lock - but you can't
acquire one because you've already read locked
Instead - First check if the variable is defined - does not require
a lock -if it's not then Write lock and Init
</cfif>
<cfset request.app=application.requestapp>
</cflock>
Just my 2-cents!
-Dustin
-----Original Message-----
From: Steve Nelson [mailto:[EMAIL PROTECTED]]
Sent: Saturday, August 26, 2000 8:34 AM
To: Fusebox
Subject: No more need for cflock!!
I've just hit upon a technique that would mean we only ever need to
use
cflock two times in a fusebox home application. This is for
application
variables, session and server variables would need to do the same
too i
imagine (personally i never use them)
First I want to propose a new filename, qry_globals.cfm the point of
the
file is to store application wide queries, it would sit in the root
directory of your home application. It would run queries from the
database upon booting up the server then store the variables into
memory. This massively reduces stress on the database, generally
it's
an excellent technique. The problem has been with cflock. people
forget to use it and CF WILL blow up on you if you forget to use
CFLOCK. So I figured out a way to bypass all the cflock nonsense
and
only require two cflocks in your entire application, which do very
small
tasks.
Check this code out. It's wicked cool (Hal let me know how I did
on my
fusedocs, i'm just starting to get into them, and love 'em! :)
<cfsetting enablecfoutputonly="yes">
<!--- qry_globals.cfm --->
<!---
|| I start by doing a check to see if the variable
application.requestapp exists if this
|| variable exists then I set request.app=application.requestapp and
I
do not rerun any
|| application wide queries. If this variable does not exist I
rerun
all the queries
|| and set application.requestapp=request.app
||
|| Then anytime I want one of these values I call it as:
request.app.queryname instead
|| of application.queryname. By doing this I no longer need to use
cflock in anywhere
|| other than this file.
|| [EMAIL PROTECTED]
||
-->
<-- request.app - this is a copy of an application variable called
application.requestapp
++> application.requestapp - this is where all application wide
queries
sit
+++
--->
<cfset request.maindsn="valuemusiclocal">
<cfapplication name="blbl"
applicationtimeout="#createtimespan(0,1,0,0)#">
<cflock name="#application.applicationname#" timeout="60"
type="readonly">
<cfif isdefined("application.requestapp")>
<cfset request.app=application.requestapp>
<cfset runrequest="no">
<cfelse>
<cfset runrequest="yes">
</cfif>
</cflock>
<cfif runrequest>
<cfset request.app=structnew()>
<cfquery name="request.app.getstates"
datasource="#request.maindsn#">
select * from states
where active=1
order by state_name
</cfquery>
<cfset request.app.state_rows=structnew()>
<cfloop query="request.app.getstates">
<cfset request.app.state_rows[state_id]=currentrow>
</cfloop>
<cflock name="#application.applicationname#" timeout="60"
type="exclusive">
<cfset application.requestapp=request.app>
</cflock>
</cfif>
<cfsetting enablecfoutputonly="no">
<!--- dsp_address.cfm --->
<!---
|| I'm demonstrating the use of a request.app variable, note that
|| I do not need cflock, and I do not need to rerun the getstates
query
|| [EMAIL PROTECTED]
||
-->
<--
++> request.app.getstates - this is a query with all the states in
it
+++
--->
<select name="state_id">
<cfoutput query="request.app.getstates">
<option value="#state_id#">#state_name#
</cfoutput>
</select>
Now that's a beautiful thing! eh?
Steve
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