Warning: already initialized constant When Multi-threading

Just notice that module.rb changed a little bit in version 1.4 and the code that actually shows the messaage is the next one, in line 37:

  JavaUtilities.create_proxy_class(constant, java_class, self)

Anthony, could you attach a test case or a script to check this problem?

We've fixed other cases like this in the past, but this should be fixed in 1.5. The problem here is that the lazy lookup and constantification of classes from a package import is not thread-safe and does not quietly ignore when the constant has already been assigne the same class in another thread.

Here's a dumb example that causes it:

require 'java'
threads = []
100.times do
  threads << Thread.new(Object.new) do |o|
    class << self
      import java.util
      ArrayList; Vector; HashMap; Collection; List; Map
    end
  end
end

threads.map(&:join)

I'm marking this intro, since the logic for package imports isn't terribly complicated, and it could be an easy one for someone to fix.

I fixed this by making the actual const set be quiet on overwrites (for this specific case) but to add a warning (for this specific path) if a constant is going to be overwritten with a different value. So this quiets your warnings, and should never warn unless there's something actually being overwritten in a destructive way. Pushed in 68f4623...and I have no idea how we'd test this, so I didn't.