RequestStore::Fibers

Ya know how sometimes you need to keep track of per-request state in a Rails app? You reach for RequestStore to do that, right? Works great.

But now you want to start using the Async gem with the Falcon server for asynchronous I/O and improved performance and scalability. Problem is, those gems work by creating fibers—and the thread-local storage that RequestStore uses is also fiber-local, so it doesn’t get passed down into child fibers. You could be in the middle of handling a request, start a new fiber to fire off an async I/O request to a service, and that fiber no longer has access to the per-request store.

Any time a fiber is created, this gem copies the RequestStore data into the new fiber’s thread-local storage.

Ruby! It’s magical! You can hook into anything, including standard library calls. I hook into Fiber.new and store Thread.current[:request_store] in a variable. Once the newly-created fiber resumes for the first time, I copy that value into the fiber’s Thread.current[:request_store].

Add this line to your application's Gemfile:

gem 'request_store-fibers'

And then execute:

$ bundle install

Or install it yourself as:

$ gem install request_store-fibers

Note that you still need the request_store gem. request_store-fibers is not a fork or a rewrite of request_store. It’s a hook that lets you use the existing request_store with fibers.

Make an initializer that does this:

RequestStore::Fibers.init

If you ever need to unhook fiber creation, here’s how:

RequestStore::Fibers.uninit

In your app, whenever you need to access the request store, you just do it the way you always did: by referencing RequestStore.

After checking out the repo, run bin/setup to install dependencies. Then, run rake spec to run the tests. You can also run bin/console for an interactive prompt that will allow you to experiment.

To install this gem onto your local machine, run bundle exec rake install. To release a new version, update the version number in version.rb, and then run bundle exec rake release, which will create a git tag for the version, push git commits and the created tag, and push the .gem file to rubygems.org.

Bug reports and pull requests are welcome on GitHub at https://github.com/BMorearty/request_store-fibers.

The gem is available as open source under the terms of the MIT License.