class ActiveSupport::Cache::MemoryStore

def cleanup(options = nil)

Preemptively iterates through all stored keys and removes the ones which have expired.
def cleanup(options = nil)
  options = merged_options(options)
  instrument(:cleanup, size: @data.size) do
    keys = synchronize { @data.keys }
    keys.each do |key|
      entry = @data[key]
      delete_entry(key, **options) if entry && entry.expired?
    end
  end
end