Cache calls to Process.pid to avoid lots of useless system calls on modern Linux.

Ruby's Process.pid calls the standard libc getpid(2), historically pretty much all implementations of the libc have been caching this function to avoid doing a syscall everytime.

However glibc 2.25 released in 2017 removed that cache, causing a performance regression for application frequently monitoring the PID.

The reason they removed it, is that some low-level libraries would fork by calling the syscall themselves, bypassing the code responsible for clearing the cache.

But doing this in Ruby is impossible, so we can safely cache the PID and save some performance.

This gem is a backport of a Ruby 3.3 feature, if you are running Ruby 3.3+ this gem is useless.

This gem only work on Ruby 3.1+, on older rubies it has no effect.

Install the gem and add to the application's Gemfile by executing:

$ bundle add pid_cache

If bundler is not being used to manage dependencies, install the gem by executing:

$ gem install pid_cache

That's it, the cache is applied immediately uppon requiring the gem, and is automatically flushed upon fork.

Note that the caching only applies to Process.pid, the $$ magic variable is unimpacted.

After checking out the repo, run bin/setup to install dependencies. Then, run rake test 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/Shopify/pid_cache.

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