register_pool

# File activerecord/lib/active_record/connection_adapters/abstract/connection_pool/reaper.rb, line 30
          def register_pool(pool, frequency) # :nodoc:
            @mutex.synchronize do
              unless @threads[frequency]&.alive?
                @threads[frequency] = spawn_thread(frequency)
              end
              @pools[frequency] ||= []
              @pools[frequency] << WeakRef.new(pool)
            end
          end