Flaws in constant caching
-------------------------
Key: JRUBY-3091
URL: http://jira.codehaus.org/browse/JRUBY-3091
Project: JRuby
Issue Type: Bug
Components: Core Classes/Modules
Reporter: Charles Oliver Nutter
Assignee: Thomas E Enebo
Priority: Blocker
Fix For: JRuby 1.1.5
In response to a report from Raphael Valyi I have discovered some crucial flaws
in the constant caching logic; some of them may not be reconcilable with the
current design.
The first is when a value previously cached gets shadowed by new value in an
intermediate module or class in the inheritance hierarchy:
{noformat}
BAR = 1
class Bar; end
class Foo < Bar
def bar; BAR; end
end
puts Foo.new.bar
Bar.const_set(:BAR, 2)
puts Foo.new.bar
{noformat}
This should print 1, then 2, but it prints 1 and 1.
The second case is when a previously cached value is shadowed by a new value in
an intermediate module or class in the containment hierarchy.
{noformat}
BAR = 1
class Bar
class Foo
def bar; BAR; end
end
end
puts Bar::Foo.new.bar
Bar.const_set(:BAR, 2)
puts Bar::Foo.new.bar
{noformat}
The first case seems like it would be caused by bad generation-twiddling. It
could probably be fixed by sorting out when generation-twiddling is not
happening and making sure it is cascading properly.
The second case, however, is a more serious problem. Because we do not
currently track cref containment from parent to child, there's no way for an
update to a cref constant scope to inform containing scopes of the change. We
would need to add a new weak list of contained crefs similar to the subclasses
list currently in RubyModule.
If we can't resolve these problems 1.1.5 will have to ship without constant
caching. I'm committing a change to temporarily disable constant caching, and I
am adding the tests I describe above.
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