[ruby-core:41129] Re: [Backport93 - Backport #5621] Please backport thread-safe autoloading patch

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(2011/11/18 14:05), Charles Oliver Nutter wrote:
>> # test.rb t1 = Thread.new { require "foo"; Foo } t2 = Thread.new
>> { require "bar"; Bar }
> 
> The problem here is caused by require having a lock per file. At
> the time it was added, I believe I warned it would cause deadlocks
> in the future.

Sure.  This deadlock from cross-require is intentional at this moment
I believe, and that's the reason for the warning 'loading in progress,
circular require considered harmful'.  Related discussion is at #920.

I don't know how Java's classloader avoids this problem.

> Yehuda's simple case could be solved by having all autoloads 
> synchronized against a single lock; only *either* the Foo autoload
> or the Bar autoload could fire, and then the other would fire once
> it had completed.

I understand that it's not an autoload issue but a concurrent require
issue, and 'disallowing concurrent requires entirely' in #920 is hard
jump for Ruby...

So I hope someone extract requirements from Yehuda's case for solving
Rails' issue, not by changing require/autoload directly.  I don't have
enough time for it now but there would be some more related
assumptions around it I guess.  For example, they don't want to let
developers write 'require' explicitly, a convention for Ruby's module
hierarchy that must sync with filesystem layout, etc...

// NaHi
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