I'm finally back to Vitória, after a great time in RubyConfBR, even
though I've been target of jokes from Aaron Patterson regarding Rspec
questions due my questions to David Chelimsky in a non-related talk from
him. But that's ok, it was fun and I deserved it :)
When listening to Yehuda's talk about development on the client side,
which was really great by the way, I got really worried when he
commented about some Rails validations not being concurrent-safe nor
even thread-safe.
While I can understand it is hard to guarantee uniqueness validation
among different server instances, this can be easily avoided in a single
server configuration with config.threadsafe! enabled.
Actually, I can't understand why thread-safe isn't enabled by default in
production, since we have much better thread support in MRI 1.9.2 and
always had on JRuby.
I've just read the documentation for validates_uniqueness_of and it
explains well the problem:
http://api.rubyonrails.org/classes/ActiveRecord/Validations/ClassMethods.html#method-i-validates_uniqueness_of
But I was thinking if Rails could provide some way for avoiding dealing
with exceptions when using a single multi-thread server environment. For
instance:
@record.validate :lock => @shared_lock do
# code run if @record.valid?
...
@record.save
end or (render :edit; return)
redirect_to :list
...
The :lock parameter should be optional and an internal lock (one per
model, maybe) should be used when not specified in the case it is not
necessary to share this code with another block which could also affect
the record, for instance.
An error should raise if 'config.threadsafe!' is not enabled and it
should be pointed out in the docs that this won't work for multiple
servers setup, for avoiding confusing end-developer users. Maybe a
warning instead of an error should suffice, for allowing this usage by
plugins that don't have control of the deployment decisions.
If the user calls 'save' directly without validating first, the
validation and save operations shoud be atomic in this case. So, 'save'
should also support the :lock parameter.
Is this reasonable or am I missing something?
Rodrigo.
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