```ruby
require "activerecord/delay_touching/version"

# Per-thread tracking of the touch state
module ActiveRecord
  module DelayTouching
    class State
      attr_accessor :nesting

      def initialize
        @records = Hash.new { Set.new }
        @already_updated_records = Hash.new { Set.new }
        @nesting = 0
      end

      def updated(attr, records)
        @records[attr].subtract records
        @records.delete attr if @records[attr].empty?
        @already_updated_records[attr] += records
      end

      # Return the records grouped by the attributes that were touched, and by class:
      # [
      #   [
      #     nil, { Person => [ person1, person2 ], Pet => [ pet1 ] }
      #   ],
      #   [
      #     :neutered_at, { Pet => [ pet1 ] }
      #   ],
      # ]
      def records_by_attrs_and_class
        @records.map {|attrs, records| [attrs, records.group_by(&:class)]}
      end

      def more_records?
        @records.present?
      end

      def add_record(record, column)
        @records[column] += [ record ] unless @already_updated_records[column].include?(record)
      end

      def clear_records
        @records.clear
        @already_updated_records.clear
      end
    end
  end
end
```

Correct the comment. It's not thread-safe.
user
```ruby
require "activerecord/delay_touching/version"

module ActiveRecord
  module DelayTouching

    # Tracking of the touch state. This class has no class-level data, so you can
    # store per-thread instances in thread-local variables.
    class State
      attr_accessor :nesting

      def initialize
        @records = Hash.new { Set.new }
        @already_updated_records = Hash.new { Set.new }
        @nesting = 0
      end

      def updated(attr, records)
        @records[attr].subtract records
        @records.delete attr if @records[attr].empty?
        @already_updated_records[attr] += records
      end

      # Return the records grouped by the attributes that were touched, and by class:
      # [
      #   [
      #     nil, { Person => [ person1, person2 ], Pet => [ pet1 ] }
      #   ],
      #   [
      #     :neutered_at, { Pet => [ pet1 ] }
      #   ],
      # ]
      def records_by_attrs_and_class
        @records.map { |attrs, records| [attrs, records.group_by(&:class)] }
      end

      def more_records?
        @records.present?
      end

      def add_record(record, column)
        @records[column] += [ record ] unless @already_updated_records[column].include?(record)
      end

      def clear_records
        @records.clear
        @already_updated_records.clear
      end
    end
  end
end
```
assistant