Potential performance improvements may be achieved under MRI by installing
optional C extensions. To minimize installation errors the C extensions are
available in the concurrent-ruby-ext extension gem. concurrent-ruby and
concurrent-ruby-ext are always released together with same version.

The concurrent-ruby gem will automatically detect the presence of the
concurrent-ruby-ext gem and load the appropriate C extensions.

WWW: https://github.com/ruby-concurrency/concurrent-ruby