[wp-hackers] Using php Sessions

[Kurt Payne]

> only one script can open a given session at a time.

To clarify: only one php process can save session data for a specific
session at a time.  This is because the file based session handling
uses file locking.

> Not a problem if you *only* ever load pages sequentially,
> but add some latency to the mix or start loading rich data
> via ajax and you compound the problem.

This is true.  The latency for sequential requests is a safety net, so
weigh the options and choose what's best for your site.

A handler that doesn't lock the session for read+write can result in
race conditions that will cause your session data to be out of sync.

request 1 -> read session
request 2 -> read session
request 1 -> write session
request 3 -> read session <-- What request 1 wrote
request 2 -> write session <-- request 3 and 2 now out of sync
request 3 -> write session <-- request 2 data now lost

--Kurt

On Thu, Mar 29, 2012 at 9:32 PM, Adam Backstrom <adam at sixohthree.com> wrote:
> On Thu, Mar 29, 2012 at 20:30, Matt Slocum <mattslocum at sharefaith.com>wrote:
>
>> Hi,
>> I'd like to keep track of some visitor's data while they browse my site and
>> modify some navigation options based on their behaviors. I could do this
>> using php's set_cookie() and store some info and make the desired
>> modifications. Using cookies is somewhat iritating because I have to do my
>> logic that I want included into the cookie before the headers are sent.
>> I've done other PHP programming on non-wordpress sites and I normally use
>> SESSIONS. I know that WordPress does not use sessions by default. It would
>> be nice to use them since I could change some of the session data after the
>> tracking cookie has been sent, and it would still persist because of the
>> nature of sessions.
>>
>> Is there any reason that I shouldn't use php sessions on my site?
>>
>> Both styles would send another cookie. I guess non-session style would use
>> fewer system resources. Is that the only reason?
>
>
> If you're using PHP's default file-based session storage, only one script
> can open a given session at a time. Subsequent scripts have to wait until
> the first releases the lock on the session file. Not a problem if you
> *only* ever load pages sequentially, but add some latency to the mix or
> start loading rich data via ajax and you compound the problem.
>
> I'm not up to date on the internal workings of Transients (read "this
> suggestion might be inefficient"), but that's one WordPress facility you
> could use for storing temporary user data. Set a cookie early in the
> request, read and modify a transient as necessary, possibly after headers
> are sent.
>
> http://codex.wordpress.org/Transients_API
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