[wp-hackers] getting the expiration value of a transient when OBJECT_CACHE is involved

[Nikola Nikolov]

It's not going to be very easy to do that.

First of all wp_cache_add() can actually be using different storage
mechanisms, or at least different implementations of the clients. For
instance the most common object cache as far as I'm aware is the Memcached
(Memcache Daemon).
In PHP there are two general classes that act as clients for - Memcache and
Memcached. Memcache is pretty plain and doesn't really give you a whole lot
to work with. Memcached I think has more possibilities, but I don't think
getting the expiration date would be one of the built-in ones.

But then there could be a caching plugin that uses a different back-end to
store objects in memory, so unless you cover all of the possibilities, then
it's not really possible to do what you're looking to do.

Is it really necessary to know when a transient will expire? You might have
to look for a way to avoid going that way :)


On Thu, Jun 26, 2014 at 9:21 PM, Haluk Karamete <halukkaramete at gmail.com>
wrote:

> In the code segment that I pasted below ( which is straight from the core -
> > option.php  ), I 'm trying to understand how I can pull the expire_time (
> the unix time stamp ) for the transient I'm after.
>
> When there is no object_cache is involved, that's a piece of ccake as
> *get_option(
> $transient_timeout )* just gets me that.
>
> <begin_snippet>
>
>     if ( wp_using_ext_object_cache() ) {
>         $value = wp_cache_get( $transient, 'transient' );
>     } else {
>         $transient_option = '_transient_' . $transient;
>         if ( ! defined( 'WP_INSTALLING' ) ) {
>             // If option is not in alloptions, it is not autoloaded and
> thus has a timeout
>             $alloptions = wp_load_alloptions();
>             if ( !isset( $alloptions[$transient_option] ) ) {
>                 $transient_timeout = '_transient_timeout_' . $transient;
>                 if ( get_option( $transient_timeout ) < time() ) {
>                     delete_option( $transient_option  );
>                     delete_option( $transient_timeout );
>                     $value = false;
>                 }
>             }
>         }
>
>         if ( ! isset( $value ) )
>             $value = get_option( $transient_option );
>     }
>
>
> <end_snippet>
>
> But on an object cache situation, such as total_cache, that's been a uphill
> battle for me.
>
> All I got there for inspiration is this;
>
> $value = wp_cache_get( $transient, 'transient' );
>
> When I traced that function ( wp_cache_get() ) down to its roots,  I end up
> with the following which did not produce any fruits neither.
>
>     /**
>      * Retrieves the cache contents from the cache by key and group.
>      *
>      * @since 2.0.0
>      * @uses $wp_object_cache Object Cache Class
>      * @see WP_Object_Cache::get()
>      *
>      * @param int|string $key What the contents in the cache are called
>      * @param string $group Where the cache contents are grouped
>      * @param bool $force Whether to force an update of the local cache
> from the persistent cache (default is false)
>      * @param &bool $found Whether key was found in the cache.
> Disambiguates a return of false, a storable value.
>      * @return bool|mixed False on failure to retrieve contents or the
> cache
>      *        contents on success
>      */
>     function wp_cache_get( $key, $group = '', $force = false, &$found =
> null ) {
>         global $wp_object_cache;
>
>         return $wp_object_cache->get( $key, $group, $force, $found );
>     }
>
>
> As you see, there is no talk on $expire there neither.
>
> Then the ball is sent to $wp_object_cache->get court...  and I got lost in
> there.
>
> Could someone shed some light where to go to get that timestamp?
>
> My goal is to be able to report back to me when the current transient will
> expire for the current page.
>
> On my local host, I display this at the bottom of the page without sweat:
>
>     This page's transient will expire in 0 day(s) 0 hour(s) 0 min(s) 30
> sec(s)
>
>
> But for the development server, I got nada. :(
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