    # File lib/rack/session/memcache.rb, line 49
          def get_session(env, sid)
            with_lock(env) do
              unless sid and session = @pool.get(sid)
                sid, session = generate_sid, {}
                unless /^STORED/ =~ @pool.add(sid, session)
                  raise "Session collision on '#{sid.inspect}'"
                end
              end
              [sid, session]
            end
          end