vendor/rails/activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb
# Check-in a database connection back into the pool, indicating that you
# no longer need this connection.
#
# +conn+: an AbstractAdapter object, which was obtained by earlier by
# calling +checkout+ on this pool.
Check-in a database connection back into the pool, indicating that you
no longer need this connection.

+conn+: an AbstractAdapter object, which was obtained by earlier by
calling +checkout+ on this pool.
Check - in a database connection back into the pool indicating that you no longer need this connection . + conn + : an AbstractAdapter object which was obtained by earlier by calling + checkout + on this pool .
def checkin(conn)
        @connection_mutex.synchronize do
          conn.run_callbacks :checkin
          @checked_out.delete conn
          @queue.signal
        end
      end
def checkin ( conn ) @connection_mutex . synchronize do conn . run_callbacks :checkin @checked_out . delete conn @queue . signal end end
Check-in a database connection back into the pool, indicating that you
no longer need this connection.
Check - in a database connection back into the pool indicating that you no longer need this connection .
conn