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Joey Hess 2012-01-17 23:26:55 -04:00
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doc/bugs/ikiwiki_overzealously_honours_locks_when_asked_for_forms.mdwn
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When an `ikiwiki` instance is holding a lock, a web user clicking on "add comment" (for example) will have to wait for the lock to be released. However, all they are then presented with is a web form. Perhaps CGI requests that are read-only (such as generating a comment form, or perhaps certain types of edits) should ignore locks? Of course, I'd understand that the submission would need to wait for a lock. — [[Jon]]
> Ikiwiki has what I think of as the Big Wiki Lock (remembering the "Big
> Kernel Lock"). It takes the exclusive lock before loading any state,
> to ensure that any changes to that state are made safely.
>
> A few CGI actions that don't need that info loaded do avoid taking the
> lock.
>
> In the case of showing the comment form, the comments
> plugin needs CGI session information to be loaded, so it can check if
> the user is logged in, and so it can add XSRF prevention tokens based on
> the session ID. (Actually, it might be possible to rely on
> `CGI::Session`'s own locking of the sessions file, and have a hook that
> runs with a session but before the indexdb is loaded.)
>
> But, the comment form also needs to load the indexdb, in order to call
> `check_canedit`, which matches a pagespec, which can need to look things
> up in the indexdb. (Though the pagespecs that can do that are unlikely
> to be relevant when posting a comment.)
>
> I've thought about trying to get rid of the Big Wiki Lock from time to
> time. It's difficult though; if two ikiwikis are both making changes
> to the stored state, it's hard to see a way to reconcile them. (There
> could be a daemon that all changes are fed thru using a protocol, but
> that's really complicated, and it'd almost be better to have a single
> daemon that just runs ikiwiki; a major architectural change.)
>
> One way that *almost* seems it could work is to have a entry path
> that loads everything read-only, without a lock. And then in read-only
> mode, `saveindex` would be an error to run. However, both the commenting
> code and the page edit code currently have the same entry path for
> drawing the form as is used for handling the posted form, so they would
> need to be adapted to separate that into two code paths. --[[Joey]]