From: Tomas Matousek <Tomas.Matousek@...>
Date: 2008-12-03T17:00:00+09:00
Subject: [ruby-core:20253] Re: autoload and concurrency

I meant that even if autoload is "fixed" by adding some kind of "in-progress" flag it wouldn't make it thread-safe since "require" itself is still broken as you described.

Tomas

-----Original Message-----
From: Charles.O.Nutter@sun.com [mailto:Charles.O.Nutter@sun.com] On Behalf Of Charles Oliver Nutter
Sent: Tuesday, December 02, 2008 10:10 PM
To: ruby-core@ruby-lang.org
Subject: [ruby-core:20251] Re: autoload and concurrency

Require could be made safe if only one thread were allowed to execute
requires at a time, globally. Whether that's a reasonable tradeoff, I'm
not sure.

All things are possible...but many require behavioral changes to Ruby.

- Charlie

Tomas Matousek wrote:
> I think it has already been concluded that autoload and require are
> inherently broken in presence of threads. See ruby-core:19860.
>
> Or am I missing something?
>
>
>
> Tomas
>
>
>
> *From:* Yehuda Katz [mailto:wycats@gmail.com]
> *Sent:* Tuesday, December 02, 2008 9:10 PM
> *To:* ruby-core@ruby-lang.org
> *Subject:* [ruby-core:20245] Re: autoload and concurrency
>
>
>
> Also, this just illustrates that it's possible. In the case of Merb, we
> aren't doing any hanky panky, and still get the bad behavior from time
> to time under high concurrency on JRuby.
>
>
>
> -- Yehuda
>
> On Tue, Dec 2, 2008 at 8:58 PM, Charles Oliver Nutter
> <charles.nutter@sun.com <mailto:charles.nutter@sun.com>> wrote:
>
> Charles Oliver Nutter wrote:
>
> Jim Deville wrote:
>
> This seems like a strong argument in favor of Ruby-core:20225.
>
>
> Fixing autoload to call require doesn't solve anything because there's
> still the exact same gap between the time it deletes the special value
> and the time when the required file redefines it.
>
>
>
> A trivial example
>
> autoloaded.rb:
>
> sleep 1
> Bar::Foo = 1
>
> autoloader.rb:
>
> module Bar
>  autoload :Foo, 'autoloaded.rb'
> end
>
> t1 = Thread.new { Bar::Foo }
> t2 = Thread.new { Bar::Foo }
> t1.join; t2.join
>
> Fails every time. Of course "sleep 1" is a longer delay than you'd
> typically see from requiring in a file, but any delay means there's a
> change another thread will schedule and see the missing constant before
> it's defined.
>
> Now some of you may be saying "don't do that". But of course, the
> developer accessing the constant *doesn't know* not to do it, and the
> developer writing the library containing the autoload just wants to
> defer a require. Who is breaking the rules?
>
> - Charlie
>
>
>
>
> --
> Yehuda Katz
> Developer | Engine Yard
> (ph) 718.877.1325
>