X-Git-Url: http://git.vanrenterghem.biz/git.ikiwiki.info.git/blobdiff_plain/294b2cd67fc6d1223d90691806b56e258ca325d2..44272d65f08e0f9f090715dca53731d776d9cc2b:/doc/post-commit/discussion.mdwn?ds=sidebyside

diff --git a/doc/post-commit/discussion.mdwn b/doc/post-commit/discussion.mdwn
index 31347a614..fc0a27ee4 100644
--- a/doc/post-commit/discussion.mdwn
+++ b/doc/post-commit/discussion.mdwn
@@ -45,3 +45,79 @@ Thanks
 > Yes, ikiwiki does expect you to use your revision control system to check
 > in changes. Otherwise, recentchanges cannot work right, since it uses the
 > commit history from your revision control system. --[[Joey]]
+
+-----
+
+I'm working on an [[rcs]] plugin for CVS, adapted from `svn.pm`, in order
+to integrate ikiwiki at sites where that's all they've got. What's working
+so far: web commit (post-commit hook and all), diff, add (under certain
+conditions), and remove. What's not working: with rcs_add(), iff any of the
+new page's parent dirs aren't already under CVS control and the post-commit
+hook is enabled, the browser and ikiwiki stall for several seconds trying
+to add it, then time out. (If I kill ikiwiki when this is happening, it cvs
+adds the topmost parent that needed adding; if I wait for timeout, it
+doesn't. I think.) If I disable the post-commit hook and do the same kind
+of thing, the page is created and saved.
+
+In case you're lucky enough not to know, cvs adds on directories are weird
+-- they operate immediately against the repository, unlike file adds:
+
+    $ cvs add randomdir
+    Directory /Users/schmonz/Documents/cvswiki/repository/ikiwiki/randomdir added to the repository
+
+I was able to work out that when I'm seeing this page save misbehavior, my
+plugin is somewhere inside `system("cvs", "-Q", "add", "$file")`, which was
+never returning. If I changed it to anything other than cvs it iterated
+correctly over all the parent dirs which needed to be added to CVS, in the
+proper order. (cvs add isn't recursive, sadly.)
+
+Can you offer an educated guess what's going wrong here? --[[Schmonz]]
+
+> Got `rcs_recentchanges` working, believe it or not, thanks to [cvsps](http://www.cobite.com/cvsps/). If I can figure out this interaction between the post-commit hook and `cvs add` on directories, the CVS plugin is mostly done. Could it be a locking issue? Where should I be looking? Any suggestions appreciated. --[[Schmonz]]
+
+>> Okay, it is definitely a locking issue. First, on the conjecture that
+>> `cvs add <directory>` was triggering the post-commit hook and confusing
+>> ikiwiki, I wrapped the ikiwiki post-commit binary with a shell script
+>> that exited 0 if the triggering file was a directory. The first half of
+>> the conjecture was correct -- my wrapper got triggered -- but the web
+>> add of `one/two/three.mdwn` (where `one` and `two` weren't existing
+>> CVS-controlled dirs) remained hung as before. There were two ikiwiki
+>> processes running. On a whim, I killed the one with the higher PID; `cvs
+>> add one` immediately completed successfully, then back to a hang and two
+>> ikiwiki processes. I killed the newer one again and then `cvs add
+>> one/two` and `cvs add one/two/three.mdwn` completed and the web add was
+>> successful. --[[Schmonz]]
+
+>>> Aaaaaand I was wrong about the second half of the conjecture being
+>>> wrong. The wrapper script wasn't correctly identifying directories;
+>>> with that fixed, everything works. I've created a
+>>> [[rcs/cvs]] page. Thanks for listening. :-)
+>>> --[[Schmonz]]
+
+>> Here is a comment I committed to my laptop from Madrid Airport before
+>> your most recent updates, in case it's still useful:
+>>
+>> Locking certianly seems likely to be a problem. ikiwiki calls `rcs_add`
+>> *before* disabling the post-commit plugin, since all over VCS allow
+>> adding something in a staged manner. You can see this in, for example,
+>> `editpage.pm` lines 391+.
+>> 
+>> So I guess what happens is that ikiwiki has taken the wiki lock, calls
+>> `rcs_add`, which does a `cvs add`, which runs the post commit hook,
+>> since it is not disabled -- which blocks waiting for the wiki lock.
+>>
+>> I guess you can fix this in either of three ways: Modify lots of places
+>> in ikiwiki to disable the post commit hook before calling `rcs_add`,
+>> or make cvs's `rcs_add` temporarily disable the commit hook and
+>> re-enable it (but only if it was not already disabled, somehow),
+>> or make cvs's `rcs_add` only make note that it needs to call `cvs add`
+>> later, and do so at `rcs_commit`. The last of these seems easist,
+>> especially since ikiwiki always commits after an add, in the same
+>> process, so you could just use a temporary list of things to add.
+>> --[[Joey]] 
+
+>>> Thanks for the comments. Attempting to set up a wiki on a different system with a different version of `cvs`, I've encountered a new locking problem within CVS: `cvs commit` takes a write lock, post-commit ikiwiki calls `rcs_update()`, `cvs update` wants a read lock and blocks. The easiest fix I can think of is to make `cvs commit` return and relinquish its lock -- so instead of my wrapper script `exec`ing ikiwiki's post-commit hook, I amp it off and exit 0. Seems to do the trick and, if I grok ikiwiki's behavior here, is not dangerous. (Beats me why my development `cvs` doesn't behave the same WRT locking.)
+
+>>> I was all set to take your third suggestion, but now that there's more than one CVS oddity fixed trivially in a wrapper script, I think I prefer doing it that way.
+
+>>> I'd be glad for the CVS plugin to be included in ikiwiki, if and when you deem it ready. Please let me know what needs to be done for that to happen. --[[Schmonz]]