[ruby-core:20259] Re: autoload and concurrency

Except that my proposed fix for autoload would have all secondary 
threads either seeing the final loaded constant value or waiting on the 
in-progress load; there would be no concurrent call to require whatsoever.

Tomas Matousek wrote:
> 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: [e-mail] [mailto:[e-mail]] On Behalf Of Charles Oliver Nutter
> Sent: Tuesday, December 02, 2008 10:10 PM
> To: [e-mail]
> 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:[e-mail]]
>> *Sent:* Tuesday, December 02, 2008 9:10 PM
>> *To:* [e-mail]
>> *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
>> <[e-mail] <mailto:[e-mail]>> 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
>>
> 
> 
>