Learning ColdFusion 8: CFThread's VARIABLES Scope Update (Thanks Dan G. Switzer, II)

Posted June 3, 2007 at 6:34 PM

Tags: ColdFusion

The other day, I posted a tutorial on ColdFusion 8's new CFThread tag, specifically, how to get data into and out of the threads. I had misunderstood the documentation when it said that all threads on the page share the same VARIABLES scope. I had taken this to mean each CHILD thread. Thankfully, Dan G. Switzer, II pointed out my misunderstanding and I was able to change the previous CFThread blog post. What Dan pointed out to me was that all the threads do indeed share the same VARIABLES scope, but that the primary page (or parent page) is also included in that pool of threads. Meaning, all threads on a given page request share the same VARIABLES scope.

To demonstrate this concept, take a look at this:

 Launch code in new window » Download code as text file »

  • <!--- Set a message into the VARIABLES scope. --->
  • <cfset VARIABLES.Message = "From Parent Page" />
  •  
  •  
  • <!--- Launch a child thread. --->
  • <cfthread
  • action="run"
  • name="ThreadOne">
  •  
  • <!---
  • Store a message into this thread's VARIABLES
  • scope. This is NOT the page's VARIABLES scope;
  • threads have their own version.
  • --->
  • <cfset VARIABLES.Message = "From Thread One!" />
  •  
  • </cfthread>
  •  
  •  
  • <!---
  • Let's wait for thread one to finish so that we know
  • exactly where all of our values are coming from.
  • Remember, these threads are asyncronous. In fact, they
  • might not even execute in the same order in which they
  • were defined.
  • --->
  • <cfthread
  • action="join"
  • name="ThreadOne"
  • />
  •  
  •  
  • <!--- Launch a child thread. --->
  • <cfthread
  • action="run"
  • name="ThreadTwo">
  •  
  • <!---
  • Get the message from the VARIABLES scope
  • and store it into this thread's publically
  • accessible THREAD scope.
  • --->
  • <cfset THREAD.Message = VARIABLES.Message />
  •  
  • </cfthread>
  •  
  •  
  • <!---
  • Join the second thread to the current page process.
  • After this, all our child threads will have finished
  • executing (and in the same order as they were declared).
  • --->
  • <cfthread
  • action="join"
  • name="ThreadTwo"
  • />
  •  
  •  
  • <!--- Output the message stored into thread two. --->
  • Thread Two: #ThreadTwo.Message#<br />
  •  
  • <!--- Output the message stored in the parent. --->
  • Parent: #VARIABLES.Message#

Notice that while I am launching two child threads, I am requesting that the parent page wait for each thread to finish processing before it executes the next. This effectively defeats the purpose of the CFThread tag, but it is necessary to show that each thread shares the same VARIABLES scope. Running the above code, we get:

Thread Two: From Thread One!
Parent: From Thread One!

What you can see by the output is that the first thread updates the message value. This change is reflected not only in the message available to the second thread, but also to the parent page.

Thanks Dan, you the man!

Download Code Snippet ZIP File

Post Comment  |  Ask Ben  |  Permalink  |  Other Searches  |  Print Page




Learning ColdFusion 9 - ColdFusion 9 tutorials, samples, examples, demos

Reader Comments

Pinal Dave
Jun 3, 2007 at 7:27 PM // reply »
3 Comments
21 Points

Good notes about ColdFusion 8.
I enjoy reading your articles.
Keep it up.
Pinal Dave


Post Comment  |  Ask Ben

Recent Blog Comments
anang
Nov 22, 2009 at 1:56 AM
Learning ColdFusion 9: Using CFQuery In CFScript Can Enable SQL Injection Attacks
Why adobe would give you script equivalent of cfquery is beyond me. I love cfquery tag because it helps me wriite clean sql, and get away from the horrible jdbc queries If I wanted to write javali ... read »
anang
Nov 22, 2009 at 1:45 AM
Streaming Text Using ColdFusion's CFContent Tag And The Variable Attribute
The reason you would want to do this is to stream. Ack json/xml files to ria clients I used thus technique before because putting json in response stream causes debugging info to come thru As well a ... read »
komik
Nov 21, 2009 at 6:47 PM
Hal Helms - Real World Object Oriented Development, Sarasota - Day Five
@charlie griefer, Thank you.. ... read »
Jody Fitzpatrick
Nov 21, 2009 at 5:15 PM
Using ColdFusion Structures To Remove Duplicate List Values
@Jose Galdamez, Oh heh yeah I didn't paste the whole code. I should have defined the vars -- my bad. It's fixed thou. Thanks. ... read »
Unibands
Nov 21, 2009 at 4:49 PM
Styling The ColdFusion 8 WriteToBrowser CFImage Output
Great work yet again Ben! Whilst I didn't use this whole code, I copied some of your regex code for a similar problem with the lack of an alt attribute and unescaped ampersands in CFIMAGE for Railo 3 ... read »
Justice
Nov 21, 2009 at 1:13 PM
My First ColdFusion Builder Extension - Encrypting And Decrypting CFM / CFC Files
@Ben, Because I am pedantic, I just want to make sure that everyone knows there is absolutely no encryption going on. There is only encoding and obfuscation. The cfencode tool only obfuscates your C ... read »
Jose Galdamez
Nov 21, 2009 at 12:28 PM
Using ColdFusion Structures To Remove Duplicate List Values
@Jody I can't seem to get your code sample to work. If you are still having problems, try this code out and see if it gets you what you wanted. <!--- Comma delimited list with various duplicates ... read »
Esther Annies
Nov 21, 2009 at 11:03 AM
Groovy Operator Overloading Does Not Work In The ColdFusion Context
Hi Ben, Thanks for this informative post. Now I am reading ur old posts too ... read »