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Explicit require of autoloaded class triggers double load #2510

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bbrowning opened this Issue Jan 23, 2015 · 5 comments

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bbrowning commented Jan 23, 2015

Explicitly requiring a class that's also marked to autoload can result in that class getting loaded twice. Normally that's not a huge problem, but in cases where the class undefs methods or something else similar it's an issue.

Here's a simple example created from a real-world ActiveSupport 4.1.8 issue I hit:

https://gist.github.com/bbrowning/cb59f764a697b93b5b6c

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headius commented Jan 23, 2015

This is a big job. Here's what we know.

JRuby 1.7 and 9k require logic looks mostly identical, so I don't think this is a bug in require. Most likely this is a bug that has always existed in how we search for loaded and loading features, and it is being exposed now because 9k is (properly, I think) expanding absolute paths at various places during load.

I started looking into MRI's logic, and it has many differences from ours.

  • search_required, which should be equivalent to our featureAlreadyLoaded, has a great deal more logic. It is extension-aware, and performs lower level searches for loaded features with the extension in mind.
  • rb_feature_p, upon which we probably based our featureAlreadyLoaded, has logic to check expanded load path entries, circular load lock ("loading" collection) and more.
  • MRI's feature_index appears to aggregate not just the file loaded for a feature, but other file paths that should match that feature.

I'm attempting a partial port, but I have other responsibilities that will pull me away from this.

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headius commented Jan 23, 2015

I started the port of search_required. Here's what I have: https://gist.github.com/headius/a78c68145e2f8c739b1e

This is mostly finished except for the goto in there.

The big snag came while attempting to port rb_feature_p, due to differences in our feature_index and how we maintain it.

We also don't have an expanded load_path as in MRI. They use this expanded load_path cache for trying different filesystem prefixes.

On the up side, if we manage to port all this logic over it could speed up require/load searching too.

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headius commented Jan 23, 2015

I will be unable to work on this for a while. Pinging @ratnikov and @Who828 since they might have interest in picking up where I left off.

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headius commented Apr 17, 2015

We actually had to fix this to get Rails working, because an autoloaded class that undef'ed a method was getting run twice (and blowing up). Should be fixed in 9k.pre2.

@headius headius closed this Apr 17, 2015

@headius headius modified the milestones: JRuby 1.7.20, 9.0.0.0.pre2 Apr 20, 2015

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headius commented Apr 20, 2015

Apparently a big problem for others on 1.7, so I backported the fixes there too.

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