with_new_connections_blocked

# File activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb, line 607
        def with_new_connections_blocked
          synchronize do
            @threads_blocking_new_connections += 1
          end

          yield
        ensure
          num_new_conns_required = 0

          synchronize do
            @threads_blocking_new_connections -= 1

            if @threads_blocking_new_connections.zero?
              @available.clear

              num_new_conns_required = num_waiting_in_queue

              @connections.each do |conn|
                next if conn.in_use?

                @available.add conn
                num_new_conns_required -= 1
              end
            end
          end

          bulk_make_new_connections(num_new_conns_required) if num_new_conns_required > 0
        end