RequestStore
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Ever needed to use a global variable in Rails? Ugh, that's the worst. If you
need global state, you've probably reached for Thread.current
. Like this:
def self.foo
Thread.current[:foo] ||= 0
end
def self.foo=(value)
Thread.current[:foo] = value
end
Ugh! I hate it. But you gotta do what you gotta do...
The problem
Everyone's worrying about concurrency these days. So people are using those
fancy threaded web servers, like Thin or Puma. But if you use Thread.current
,
and you use one of those servers, watch out! Values can stick around longer
than you'd expect, and this can cause bugs. For example, if we had this in
our controller:
def index
Thread.current[:counter] ||= 0
Thread.current[:counter] += 1
render :text => Thread.current[:counter]
end
If we ran this on MRI with Webrick, you'd get 1
as output, every time. But if
you run it with Thin, you get 1
, then 2
, then 3
...
The solution
Add this line to your application's Gemfile:
gem 'request_store'
And change the code to this:
def index
RequestStore.store[:foo] ||= 0
RequestStore.store[:foo] += 1
render :text => RequestStore.store[:foo]
end
Yep, everywhere you used Thread.current
just change it to
RequestStore.store
. Now no matter what server you use, you'll get 1
every
time: the storage is local to that request.
API
The fetch
method returns the stored value if it already exists. If no stored value exists, it uses the provided block to add a new stored value.
top_posts = RequestStore.fetch(:top_posts) do
# code to obtain the top posts
end
Rails 2 compatibility
The gem includes a Railtie that will configure everything properly for Rails 3+ apps, but if your app is tied to an older (2.x) version, you will have to manually add the middleware yourself. Typically this should just be a matter of adding:
config.middleware.use RequestStore::Middleware
into your config/environment.rb.
No Rails? No Problem!
A Railtie is added that configures the Middleware for you, but if you're not using Rails, no biggie! Just use the Middleware yourself, however you need. You'll probably have to shove this somewhere:
use RequestStore::Middleware
No Rails + Rack::Test
In order to have RequestStore
storage cleared between requests, add it to the
app
:
# spec_helper.rb
def app
Rack::Builder.new do
use RequestStore::Middleware
run MyApp
end
end
Using with Sidekiq
This gem uses a Rack middleware to clear the store object after every request, but that doesn't translate well to background processing with Sidekiq.
A companion library, request_store-sidekiq creates a Sidekiq middleware that will ensure the store is cleared after each job is processed, for security and consistency with how this is done in Rack.
Semantic Versioning
This project conforms to semver. As a result of this policy, you can (and should) specify a dependency on this gem using the Pessimistic Version Constraint with two digits of precision. For example:
spec.add_dependency 'request_store', '~> 1.0'
This means your project is compatible with request_store 1.0 up until 2.0. You can also set a higher minimum version:
spec.add_dependency 'request_store', '~> 1.1'
Contributing
- Fork it
- Create your feature branch (
git checkout -b my-new-feature
) - Commit your changes (
git commit -am 'Add some feature'
) - Push to the branch (
git push origin my-new-feature
) - Create new Pull Request
Don't forget to run the tests with rake
.