RuboCop::ThreadSafety

Thread-safety analysis for your projects, as an extension to RuboCop.

Installation and Usage

Installation into an application

Add this line to your application's Gemfile (using require: false as it's a standalone tool):

gem 'rubocop-thread_safety', require: false

Install it with Bundler by invoking:

$ bundle

Add this line to your application's .rubocop.yml:

plugins: rubocop-thread_safety

Now you can run rubocop and it will automatically load the RuboCop Thread-Safety cops together with the standard cops.

Note

The plugin system is supported in RuboCop 1.72+. In earlier versions, use require instead of plugins.

Scanning an application without adding it to the Gemfile

Install the gem:

$ gem install rubocop-thread_safety

Scan the application for just thread-safety issues:

$ rubocop --plugin rubocop-thread_safety --only ThreadSafety,Style/GlobalVars,Style/ClassVars,Style/MutableConstant

Configuration

There are some added configuration options that can be tweaked to modify the behaviour of these thread-safety cops.

Correcting code for thread-safety

There are a few ways to improve thread-safety that stem around avoiding unsynchronized mutation of state that is shared between multiple threads.

State shared between threads may take various forms, including:

• Class variables (@@name). Note: these affect child classes too.
• Class instance variables (@name in class context or class methods)
• Constants (NAME). Ruby will warn if a constant is re-assigned to a new value but will allow it. Mutable objects can still be mutated (e.g. push to an array) even if they are assigned to a constant.
• Globals ($name), with the possible exception of some special globals provided by ruby that are documented as thread-local like regular expression results.
• Variables in the scope of created threads (where Thread.new is called).

Improvements that would make shared state thread-safe include:

• freeze objects to protect against mutation. Note: freeze is shallow, i.e. freezing an array will not also freeze its elements.
• Use data structures or concurrency abstractions from concurrent-ruby, e.g. Concurrent::Map
• Use a Mutex or similar to synchronize access.
• Use ActiveSupport::CurrentAttributes
• Use RequestStore
• Use Thread.current[:name]

Certain system calls, such as chdir, affect the entire process. To avoid potential thread-safety issues, it's preferable to use (if possible) the chdir option in methods like Kernel.system and IO.popen rather than relying on Dir.chdir.

Useful resources

• Intro to thread-safety in Ruby by Socketry: https://socketry.github.io/async/guides/thread-safety/index.html

Development

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 tags, and push the .gem file to rubygems.org.

Contributing

Bug reports and pull requests are welcome on GitHub at https://github.com/rubocop/rubocop-thread_safety.

Copyright

Portions Copyright (c) 2016-2023 Michael Gee and contributors. Portions Copyright (c) 2016-2023 CoverMyMeds.

See LICENSE.txt for further details.