Restart of session doesn't work

[DavidKloucek]

I need to close session before long-runing operation, because unclosed session blocks other processes.

$session->start();
//working with session..
$session->close();

//long-running operation

$session->start();
//working with session..
$session->close();

It returns "headers already sent..". Cookie should not be sends again, if I call start() more times, or not?
Sorry for my English.

[fprochazka]

I agree that cookie should be sent only once.

[mishak87]

Nette\Http\Session is a singleton wrapper for PHP bugs, quirks and insecurities. start is a lazy singleton initialization and close does cleanup, they are not closed pair.

Ad-hoc fix: Don't send output to user before starting session for second time.

Solution: Create basket for data, store it in different storage (ie.: database) and its id in session. Flush headers immediately. Work... Then update basket and store it again.
I wouldn't store anything produced by long running script to session, it introduces more problems then it solves.