Implement RFC: Introduce session_start() options - read_only, unsafe_lock, lazy_write and lazy_destroy

[yohgaki]

Implement RFC
https://wiki.php.net/rfc/session-lock-ini
"read_only" and "lazy_lock" are accepted. PR is made for other people to review.

Except comments, changes are minimal, but includes a few bug fixes that tests equality of PS(session_status) against "php_session_none". The comparison must be "PS(session_status) != php_session_active" as it has php_session_disabled.

Comments are appreciated.

[yohgaki]

Test passes for non ZTS build. ZTS build failure seem to happen w/o this PR.
I'll merge this after I write up the UPGRADING. If anyone has comments, please do now.

[yohgaki]

Document is updated. Please review them. Thank you.

[smalyshev]

typo - accepts

[yohgaki]

Thanks! Fixed.

[yohgaki]

I've tried to get some benchmarks. It seems current system is too fast to get obvious performance difference.

Test command: ab -c 7 -n 500000 http://localhost:8888/session.php
Test script:

<?php
ini_set('session.save_path', '/home/tmp');
ini_set('session.lazy_write', 1); // Change mode here
ini_set('session.use_strict_mode', 0);

session_id('testid');
session_start(['read_and_close'=>0]); // Change mode here
//$_SESSION['test'] = ++$_SESSION['test'];
$_SESSION['a'] = str_repeat('a', 102400);
echo '<pre>';
var_dump(session_id(), $_SESSION['test']); 

Old behavior was around 15000 reqs/sec.
"read_and_close" improved it to about 20000 reqs/sec. i.e 33% faster.
"lazy_write" did not improve # of reqs, but per process httpd disk writes was reduced from 100 MB/s to 5 MB/s. i.e. There were 12 httpd processes, 1200 MB/s writes was reduced to 60 MB/s writes.

I think this would be good enough benchmark for merging.