instance method acquire_connection

# File activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb, line 1156
        def acquire_connection(checkout_timeout)
          # NOTE: we rely on <tt>@available.poll</tt> and +try_to_checkout_new_connection+ to
          # +conn.lease+ the returned connection (and to do this in a +synchronized+
          # section). This is not the cleanest implementation, as ideally we would
          # <tt>synchronize { conn.lease }</tt> in this method, but by leaving it to <tt>@available.poll</tt>
          # and +try_to_checkout_new_connection+ we can piggyback on +synchronize+ sections
          # of the said methods and avoid an additional +synchronize+ overhead.
          if conn = @available.poll || try_to_queue_for_background_connection(checkout_timeout) || try_to_checkout_new_connection
            conn
          else
            reap
            # Retry after reaping, which may return an available connection,
            # remove an inactive connection, or both
            if conn = @available.poll || try_to_queue_for_background_connection(checkout_timeout) || try_to_checkout_new_connection
              conn
            else
              @available.poll(checkout_timeout)
            end
          end
        rescue ConnectionTimeoutError => ex
          raise ex.set_pool(self)
        end