Side-effect caching support
| Project: | Drupal |
| Version: | 7.x-dev |
| Component: | base system |
| Category: | feature request |
| Priority: | normal |
| Assigned: | David Strauss |
| Status: | needs work |
Currently, caching has limited easy use because side-effecting operations are not repeated when the cached item is loaded.
For example, a function building the front page might return the content but also add a stylesheet and an RSS feed header. If only the results of the front-page-building function are cached, loading the cached version requires either manually repeating the side effects or awkwardly storing the side-effects in the cache for replay. As function calls get deeper, predicting and replaying these side effects becomes very difficult.
We could improve such caching by having a hook_side_effect that is called whenever side-effecting operations run. hook_side_effect would be called with the function name (e.g. 'drupal_add_js') and the array of arguments the function received. Caching modules could implement the hook to record and replay side effects when the cached item is retrieved.
#1
Add this:
module_invoke_all('side_effect', __FUNCTION__, func_get_args());to following are side-effecting functions:
This will allow caching modules to log and replay side-effects on cache restoration.
#2
Whoops, didn't notice that the title changed the entire bug/feature report. Should have read the descriptive text...
#3
Here's a patch to a current HEAD checkout. I tried to minimize the hook calls to when actual effects happen. I'm sure this could be improved further.
#4
I'd like feedback over whether its better to implement this as a hook or to simply compare the arrays before a function call and after to identify additions. The latter would be more complicated but possibly faster in the common case (no cache).
#5
Given the arbitrary values for $scope for drupal_get_js() and the inability to simply load the whole array for all scopes, it seems impossible to determine what core side-effects a function has used by probing for changes.
#6
Here's an alternative patch that at least allows retrieving the entire array of JavaScript for all scopes. This has a clear performance advantage over adding hook_side_effect, but it's not as extensible. hook_side_effect could be used to record arbitrary side-effecting calls. This alternative patch would require the cache to probe for side effects in specific places.
Of course, a hybrid approach is possible, too. The cache could probe core modules for side effects but still implement hook_side_effect for arbitrary additional effects.
#7
You got a TAB in there. Use two spaces instead for indents.
#8
Updated to remove tab.
#9
#10
Heh, you added some trailing whitespace in there now. Not trying to be a pain in the ass, I swear.
#11
No biggie. Whitespace removed.
#12
No longer applies.
#13
Not sure about this. I like the more extensible original idea. This would be an API change though. Tempted to move this to the D7 queue.