# ActiveSupport "is not missing constant" errors **URL:** \ **Category:** Ruby\ **Created:** [June 15, 2009, 9:28pm UTC](https://www.ruby-forum.com/t/activesupport-is-not-missing-constant-errors/170314 "2009-06-15T21:28:22Z")\ **Posts on this page:** 7\ **Page:** 1
**Author:** ![murfhy](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/d26b3c/32.png) [@murfhy](https://www.ruby-forum.com/u/murfhy)\ **Post date:** [June 15, 2009, 9:28pm UTC](https://www.ruby-forum.com/t/activesupport-is-not-missing-constant-errors/170314/1 "2009-06-15T21:28:22Z")
I’ve gone spelunking through ActiveRecord’s dependencies.rb until my eyes bleed, and I’m still yet to understand what causes these errors and how can they can be prevented. As far as I can tell, ActiveSupport’s const\_missing callback is triggered. ActiveSupport then attempts automatic code loading, only to discover that the constant is, in fact, already defined. I am specifically encountering this problem trying to use a dependency-resolving code loader: [http://github.com/tarcieri/require\_all/tree/master](http://github.com/tarcieri/require_all/tree/master) I’ve encountered this problem using Merb’s code loader as well (albeit outside of Merb). Merb’s code loader works in the same way so I’m wondering if this issue comes up with Merb as well. In the latest case, the code loads in through the code loader correctly, however when it tried to access a particular constant in a method body, the error is generated, even though the class has been loaded. This doesn’t even happen consistently either: it is happening on one of my coworker’s computers (and only his computer, even though his setup is virtually identical to our CI server). Also, it occurs only when the full Rails environment is loaded, not in unit tests. _sigh_ This has been a perpetual thorn in my side for over a year. I really have to wonder? 1. What does this “error” really mean? 2. Why is it an error? 3. Why can’t ActiveSupport handle it internally? 4. What am I expected to do in order to fix it? ---
**Author:** ![murfhy](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/d26b3c/32.png) [@murfhy](https://www.ruby-forum.com/u/murfhy)\ **Post date:** [June 18, 2009, 5:22am UTC](https://www.ruby-forum.com/t/activesupport-is-not-missing-constant-errors/170314/2 "2009-06-18T05:22:06Z")
_tumbleweeds_ Okay, different question… does anyone know who specifically I can contact about this question? Is there a more appropriate mailing list I should be asking this on? ---
**Author:** ![murfhy](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/d26b3c/32.png) [@murfhy](https://www.ruby-forum.com/u/murfhy)\ **Post date:** [June 18, 2009, 7:28am UTC](https://www.ruby-forum.com/t/activesupport-is-not-missing-constant-errors/170314/3 "2009-06-18T07:28:56Z")
Tony A. wrote: > _tumbleweeds_ > > Okay, different question… does anyone know who specifically I can contact > about this question? Is there a more appropriate mailing list I should be > asking this on? Yes, you should be asking this question on the rails list. But for what it’s worth, I’ve had that kind of problem before when the rails auto-loading magic is triggered in threads; i.e. it’s not thread-safe. Daniel ---
**Author:** ![murfhy](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/d26b3c/32.png) [@murfhy](https://www.ruby-forum.com/u/murfhy)\ **Post date:** [June 18, 2009, 8:01am UTC](https://www.ruby-forum.com/t/activesupport-is-not-missing-constant-errors/170314/4 "2009-06-18T08:01:47Z")
On Wed, Jun 17, 2009 at 11:54 PM, Tony A. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > But for what it’s worth, I’ve had that kind of problem before when the > > > rails auto-loading magic is triggered in threads; i.e. it’s not thread-safe. > > Why not? And more to the point: how can you implement this sort of automatic code loading so it works alongside ActiveSupport? ---
**Author:** ![murfhy](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/d26b3c/32.png) [@murfhy](https://www.ruby-forum.com/u/murfhy)\ **Post date:** [June 18, 2009, 8:00am UTC](https://www.ruby-forum.com/t/activesupport-is-not-missing-constant-errors/170314/5 "2009-06-18T08:00:36Z")
On Wed, Jun 17, 2009 at 11:28 PM, Daniel DeLorme [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > Yes, you should be asking this question on the rails list. The idea that Rails core doesn’t read ruby-talk confounds me. > But for what it’s worth, I’ve had that kind of problem before when the > rails auto-loading magic is triggered in threads; i.e. it’s not thread-safe. Why not? ---
**Author:** ![murfhy](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/d26b3c/32.png) [@murfhy](https://www.ruby-forum.com/u/murfhy)\ **Post date:** [June 18, 2009, 7:39pm UTC](https://www.ruby-forum.com/t/activesupport-is-not-missing-constant-errors/170314/6 "2009-06-18T19:39:39Z")
On Thu, Jun 18, 2009 at 7:46 AM, Rick DeNatale [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid)wrote: > I’m not sure I know how. Even if autoload were thread safe, I think > you’re approach, which if I remember it correctly, of trying to > explicitly require files until things work, is prone to confusing or > being confused by code using autoload. Well, it’s not “my approach” per se, it’s the same approach used by Merb So I suppose I’m curious why more people don’t experience this problem when using ActiveRecord/ActiveSupport in conjunction with Merb (or for that matter, Rails 3.0) ---
**Author:** ![murfhy](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/d26b3c/32.png) [@murfhy](https://www.ruby-forum.com/u/murfhy)\ **Post date:** [June 18, 2009, 3:47pm UTC](https://www.ruby-forum.com/t/activesupport-is-not-missing-constant-errors/170314/7 "2009-06-18T15:47:41Z")
On Thu, Jun 18, 2009 at 1:57 AM, Tony A.[removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > On Wed, Jun 17, 2009 at 11:54 PM, Tony A. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > > > But for what it’s worth, I’ve had that kind of problem before when the > > > > > rails auto-loading magic is triggered in threads; i.e. it’s not thread-safe. > > > > Why not? Probably because autoload in Ruby (which ActiveSupport now uses to implement loading missing constants) isn’t and it appears to be difficult to make it so: [http://redmine.ruby-lang.org/issues/show/921](http://redmine.ruby-lang.org/issues/show/921) > And more to the point: how can you implement this sort of automatic code > loading so it works alongside ActiveSupport? I’m not sure I know how. Even if autoload were thread safe, I think you’re approach, which if I remember it correctly, of trying to explicitly require files until things work, is prone to confusing or being confused by code using autoload. – Rick DeNatale Blog: [http://talklikeaduck.denhaven2.com/](http://talklikeaduck.denhaven2.com/) Twitter: [http://twitter.com/RickDeNatale](http://twitter.com/RickDeNatale) WWR: [http://www.workingwithrails.com/person/9021-rick-denatale](http://www.workingwithrails.com/person/9021-rick-denatale) LinkedIn: [http://www.linkedin.com/in/rickdenatale](http://www.linkedin.com/in/rickdenatale)