Years ago, when Adobe ColdFusion introduced the CFThread tag for effortless asynchronous programming in CFML, they made a decision to not allow your application to spawn nested threads. This limitation was likely put in place to ensure thread safety and prevent potential issues with concurrent execution. However, many developers believe that this constraint is unnecessary and may hinder the flexibility of their applications.

I recently encountered this issue myself while trying to log an error to BugSnag using a non-blocking HTTP call inside a thread. The ColdFusion message I received indicated that I was not running in a child-thread context, which led me to investigate further. After digging into the documentation and testing various methods, I discovered that Adobe ColdFusion does not have a built-in function like Lucee's IsInThread() or CFML's IsUnderCFThread(). Instead, I found the isUnderCFThread() method in the getPageContext() object.

This led me to explore the possibility of polyfilling the IsInThread() functionality using the isUnderCFThread() method. I created a test code snippet that demonstrates this approach and provides output from both inside and outside a CFThread tag.

<cfif not(isUnderCFThread())>
    <p>Not in child-thread context</p>
</cfif>
<cfthread>
    <cfif not(isUnderCFThread())>
        <p>In child-thread context</p>
    </cfif>
</cfthread>
<cfif not(isUnderCFThread())>
    <p>Not in child-thread context</p>
</cfif>

The output of this test indicates that the isUnderCFThread() method accurately identifies whether you are running in a child-thread context. This polyfill can be used to achieve similar functionality to Lucee's IsInThread() until Adobe ColdFusion officially introduces a built-in function for this purpose.

While the isUnderCFThread() method provides a reliable way to detect child-thread contexts, it's essential to note that there may be edge cases where this behavior differs from expectations. Developers should exercise caution when using this polyfill and consider the potential implications on their application's stability.

For developers who prefer not to rely on undocumented methods or coincidental behaviors, alternative approaches can be employed. Mark Mandel shared an approach in 2007 for testing CFThread context by examining the "current Java thread group." Although this method may not be suitable for all developers, it demonstrates a possible way to determine child-thread contexts without relying on ColdFusion-specific functions.

Another approach is to use a brute-force technique, where you try spawning a temporary thread and checking if an exception is raised. This method provides a clear indication of whether you are running in a child-thread context but may not be the most elegant solution.

Adobe ColdFusion's restriction on nested CFThread execution remains a contentious issue among developers. While some argue that this limitation ensures thread safety, others believe it hinders the flexibility of their applications. As Adobe continues to evolve and improve its products, it is essential for them to reconsider this limitation and provide a more comprehensive solution.

Developers who would like to see Adobe ColdFusion remove this restriction can file feature requests or suggest alternative approaches. In the meantime, polyfills like the one demonstrated in this article can help developers work around this limitation until a more permanent solution is introduced. Share your thoughts and suggestions with the ColdFusion community by leaving a comment below.

Want to use code from this post? Check out the license information provided at the top of the article.