register_pool

# File activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb, line 322
          def register_pool(pool, frequency) # :nodoc:
            @mutex.synchronize do
              unless @pools.key?(frequency)
                @pools[frequency] = []
                spawn_thread(frequency)
              end
              @pools[frequency] << WeakRef.new(pool)
            end
          end