[Rubygems-developers] Gem autoloading problems

Eric Hodel drbrain at segment7.net
Fri Apr 18 16:56:44 EDT 2008

On Apr 18, 2008, at 06:07 AM, Donavan Pantke wrote:
> On Friday 18 April 2008 04:01:01 am Eric Hodel wrote:
>> On Apr 17, 2008, at 22:38 PM, Chad Woolley wrote:
>>> On Thu, Apr 17, 2008 at 8:23 PM, Eric Hodel <drbrain at segment7.net>
>>> wrote:
>>>> A user of RubyGems can already control which gem gets activated  
>>>> with
>>>> Kernel#gem.  However, it is up to the user to activate the gems  
>>>> they
>>>> need in dependency order.  `gem lock` can help with this.
>>> Try GemInstaller.  It should be able to provide all the control you
>>> need over gem activation, and autoinstall all required versions as
>>> well.  If you can't make it do what you need, let me know.
>> This problem is, given a-1, a-2, and b-1 which depends on any a:
>> gem 'b'
>> fork {
>>   gem 'a', '1' # raises as a-2 is active
>> }
> Correct. I also tested to ensure that the behavior was consistent,  
> and it was
> all the way back to 0.9.0, and it is consistent as you suggested.  
> Sorry bout
> that.
>> The solutions I see are:
>> Don't list 'a' as a dependency.
> Easy to do, but at that point the metadata doesn't describe the data  
> well.
>> exec after fork to clear memory.
> Well, since the entire point of preloading in this case is to avoid  
> an exec
> and the memory overhead associated with loading the libraries again,  
> that
> doesn't work well.

How well does this work?  Doesn't the garbage collector touch the  
majority of your pages the first time it runs un-sharing most of the  
memory saved?  I've never actually measured it, but common knowledge  
seems to be that fork() to save memory via COW usually doesn't save  
much with Ruby.

>> Be careful not to require any files from 'a' and remove 'a' from the
>> set of active gems.  (Hard)
> Actually, some of this harkens back to an earlier thread about  
> categories of
> dependencies and their handling. In this case, the desired behavior of
> add_dependency in the specification was to influence the installer  
> to ensure
> that the right gems with the right versions were installed.  
> Installed, but
> not necessarily activated.

I'm not coming up with a good solution that fails in a sensible way.   
Your usecase is unique in this respect, and I think RubyGems simply  
fails it.  :)

> My suggestion right away is just to remove the
> dependency, but this may make a small, easy to implement portion of  
> the
> system. The code should be much simpler because we're not really  
> complicating
> things much.

I think most people know that Passenger requires Rails, so this may be  
the best solution. :)

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