/usr/lib/ruby/vendor_ruby/em/deferrable/pool.rb is in ruby-eventmachine 1.0.3-4.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 | warn "EM::Deferrable::Pool is deprecated, please use EM::Pool"
EM::Deferrable::Pool = EM::Pool
|