Description

The cfthread tag enables you to create threads, independent streams of code execution, in your ColdFusion application. You use this tag to run or end a thread, temporarily stop thread execution, or join together multiple threads.

Category

Application framework tags

Syntax

join
    <cfthread
    required
    name="thread name[,thread name]..."
    optional
    action="join"
    timeout="milliseconds"/>

run
    <cfthread
    required
    name="thread name"
    optional
    action="run"
    priority="NORMAL|HIGH|LOW"
    zero or more application-specific attributes>

        Thread code

    </cfthread>

sleep
    <cfthread
    required
    action="sleep"
    duration="milliseconds"/>

terminate
    <cfthread
    required
    action="terminate"
    name="thread name"/>

For all actions except run, the cfthread tag must have an empty body and be followed immediately by a </cfthread> end tag, or must have no end tag and have a slash before the tag closure, as in <cfthread action="sleep" duration="1000"/>.

See also

Sleep, "Using ColdFusion Threads" 95 in the ColdFusion Developer's Guide

History

ColdFusion 8: Added this tag

Attributes

Usage

Page-level code (code outside any cfthread tags) executes in its own thread, referred to as the page thread. Only the page thread can create other threads. A thread that you create cannot create a child thread.

ColdFusion makes a complete (deep) copy of all the attribute variables before passing them to the thread, so the values of the variables inside the thread are independent of the values of any corresponding variables in other threads, including the page thread. Thus, the values passed to threads are thread safe because the attribute values cannot be changed by any other thread.

Thread scopes

Each thread has three special scopes:

• The thread-local scope is an implicit scope that contains variables that are available only to the thread, and exist only for the life of the thread.
• The Thread scope is available to the page and to all other threads started from the page. Its data remains available until the page and all threads started from the page finish, even if the page finishes before the threads complete processing.
• The Attributes scope contains attributes that are passed to the scope, and is available only within the thread and only for the life of the thread.

For detailed information about using ColdFusion scopes in threads, see "Using ColdFusion Threads" 95 in the ColdFusion Developer's Guide.

All threads in a page share a single Variables scope, so you can use it for data that is common across all threads. You must be careful to lock access to the variables, if necessary, to prevent deadlocks or race conditions between threads.

Metadata variables

The thread scope contains the following variables that provide information about the thread (metadata):

Example

The following example uses three threads to get the results of three RSS feeds. The user must submit the form with all three feeds specified. The application joins the threads with a time-out of 6 seconds, and displays the feed titles and the individual item titles as links.

<!--- Run this code if the feed URL form has been submitted. --->
<cfif isDefined("Form.submit")>
    <cfloop index="i" from="1" to="3">
        <!--- Use array notation and string concatenation to create a variable
                 for this feed. --->
        <cfset theFeed = Form["Feed"&i]>
        <cfif theFeed NEQ "">
            <!--- Use a separate thread to get each of the feeds. --->
            <cfthread action="run" name="t#i#" feed="#theFeed#">
                <cffeed source="#feed#" 
                    properties="thread.myProps" 
                    query="thread.myQuery">
            </cfthread>
        <cfelse>
            <!--- If the user didn't fill all fields, show an error message. --->
            <h3>This example requires three feeds.<br />
            Click the Back button and try again.</h3>
            <cfabort>
        </cfif>
    </cfloop>

    <!--- Join the three threads. Use a 6 second time-out. --->
    <cfthread action="join" name="t1,t2,t3" timeout="6000" />
    
    <!--- Use a loop to display the results from the feeds. --->
    <cfloop index="i" from="1" to="3">
        <!--- Use the cfthread scope and associative array notation to get the
                Thread scope dynamically. --->
        <cfset feedResult=cfthread["t#i#"]>
        <!--- Display feed information only if you got items,
                 for example the feed must complete before the join. --->
        <cfif isDefined("feedResult.myQuery")>
            <cfoutput><h2>#feedResult.myProps.title#</h2></cfoutput>
            <cfoutput query="feedResult.myQuery">
                <p><a href="#RSSLINK#">#TITLE#</a></p>
            </cfoutput>
        </cfif>
    </cfloop>

</cfif>

<!--- The form for entering the feeds to aggregate. --->
<cfform>
    <h3>Enter three RSS Feeds</h3>
    <cfinput type="text" size="100" name="Feed1" validate="url"
        value="http://rss.adobe.com/events.rss?locale=en"><br />
    <cfinput type="text" size="100" name="Feed2" validate="url"
        value="http://weblogs.macromedia.com/dev_center/index.rdf"><br />
    <cfinput type="text" size="100" name="Feed3" validate="url" 
        value="http://rss.adobe.com/studio.rss?locale=en"><br />
    <cfinput type="submit" name="submit">
</cfform>