Handling a slow process in a Model-Glue (or other MVC) application

This weekend I exchanged a few emails with a reader about how you can handle very slow processes in a Model-Glue application. Typically folks will handle slow processes using one of these methods:

  • cfflush: Print out a 'Please Wait' type message, use cfflush to flush out the content, and then start the slow process
  • cfthread: You can use cfthread to either run a bunch of parallel slow processes at once, or 'fire and forget' a slow process
  • scheduler: Use the ColdFusion scheduler to run the slow process completely outside the view of the site visitor. </ul> Of course the best way to handle a slow process is to ensure you've done everything possible to speed it up. As an example, I was convinced that a particular process on coldfusionbloggers.org was slow because it had to be. Turned out it was a stupid SQL mistake on my part. So before any attempt is made to mitigate or hide a slow process, you need to do everything possible to ensure you haven't missed something obvious. Once you've done that, what next? If you ever tried to use cfflush within a Model-Glue view, you know what happens:

    Message Unable to perform cfflush.
    Detail You have called cfflush in an invalid location, such as inside a cfquery or cfthread or between a CFML custom tag start and end tag.

    Because your view file ends up being run as a custom tag (behind the scenes) you can't use the cfflush tag. So what about cfthread? I created a simple demo application (available as a zip to this blog entry) using Model-Glue 3. I began by creating a new event, page.slow, that would represent my slow process: <event-handler name="page.slow"> <broadcasts> <message name="doItSlow" /> </broadcasts> <results> <result do="template.main" /> </results> <views> <include name="body" template="pages/slow.cfm" /> </views> </event-handler> The doItSlow controller method is where I put my slow process: <cffunction name="doItSlow" access="public" output="false"> <cfargument name="event" type="any" required="true"> <!--- First, am I running the slow process? ---> <cfif structKeyExists(application, "slowprocess")> <cfset arguments.event.setValue("status", "ongoing")> <cfset arguments.event.setValue("progress", application.slowprocess)> <cfelse> <cfset arguments.event.setValue("status", "began")> <cfthread name="slowprocess" priority="low"> <cfset application.slowprocess = 0> <!--- run 10 processes that take 1 minute each. ---> <cfloop index="x" from="1" to="10"> <cfset application.slowprocess++> <cfset sleep(15000)> </cfloop> <cfset structDelete(application, "slowprocess")> </cfthread> </cfif> </cffunction> There are two main things happening in this method. If I see that a particular application variable doesn't exist, I begin the process within a cfthread block. I use an application variable, slowprocess, to both signify that I've begun the process and to record how far along I am. If the application variable does exist, note how I use the event object to record what's going on and how far along we are. Now I don't think you would normally be running the slow process from the controller. This would typically be in the model with the controller simply firing it off and asking a service object (for example) for an update on what's going on. I only used the controller here for everything since I wanted a quick demo. The view is interesting. I'm going to display the current status and do an automatic reload: <cfset status = event.getValue("status")> <cfset progress = event.getValue("progress")> <cfset event.setValue("usemeta",true)> <cfoutput> <b>status=</b>#status#<br/> <b>progress=</b>#progress# </cfoutput> The usemeta is simply a flag to my template view: <cfset usemeta = event.getValue("usemeta", false)> <html> <head> <link rel="stylesheet" type="text/css" href="css/stylesheet.css"></link> <cfif isBoolean(usemeta) and usemeta> <meta http-equiv="refresh" content="10"> </cfif> </head> <body> <div id="banner">Demo</div> <!--- Display the view named "body" ---> <cfoutput>#viewCollection.getView("body")#</cfoutput> </body> </html> So the end result is - the person starts the process and can just sit back and watch as the page gives an updated status on the process. Again - this is just a quick demo. It isn't best practice or anything. (In fact, it will continuously reload the process.) So I was going to stop there. But why stop when you can try something cool? Many moons ago I blogged about XML/SWF Charts, a cheap, and very sexy, charting engine. One of the coolest feature is it's ability to point to an XML file to both configure the chart and create an auto-reload data set for the chart. What follows is video of a modified version (also in the zip) where the chart engine itself runs the request for the status. The resulting data is output in the XML format required for the chart. </param> </param> </param> </param> </param> </param> </param> </embed> I'm really impressed by this charting engine. It may not be as easy as cfchart, but it is certainly as pretty, and the auto-update for data is worth the price in itself. So outside of the pretty charts - have folks done anything like the above code? (Again, ignoring the fact I used the controller.)

    Download attached file.

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