Print the call stacks in a multithread application, say puma, to know which threads are blocked

puma.rb

before_fork do
  trap 'TTIN' do
    Thread.list.each do |thread|
      puts "\nThread TID-#{thread.object_id.to_s(36)}"
      puts thread.backtrace.join("\n")
      puts "\n"
    end
  end
end