2007-10-31 22:17:03 +01:00
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I was suprised to receive two mails from ikiwiki about one web edit:
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2007-10-31 22:21:13 +01:00
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1 F Oct 30 To joey+ikiwiki update of ikiwiki's plugins/contrib/gallery.mdwn by http://arpitjain11.myopenid.com/
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1 F Oct 30 To joey+ikiwiki update of ikiwiki's plugins/contrib/gallery.mdwn by http://arpitjain11.myopenid.com/
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2007-10-31 22:17:03 +01:00
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The first of these had the correct diff for the changes made by the web
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edit (00259020061577316895370ee04cf00b634db98a).
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But the second had a diff for modifications I made to ikiwiki code
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around the same time (2a6e353c205a6c2c8b8e2eaf85fe9c585c1af0cd).
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I'm now fairly sure a race is involved. Note that the name of the modified
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page is correct, while the diff was not. The git rcs_commit code first
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gets the list of modified page(s) and then gets the diff, and apparently my
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other commit happened in the meantime, so HEAD changed.
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Seems that the rcs_notify for git assumes that HEAD is the commit
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that triggered the ikiwiki run, and that it won't change while the function is
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running. Both assumptions are bad. Git does no locking and another commit
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can come in at any time.
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Notice that the equivilant code for subversion is careful to look at $REV.
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git's post-update hook doesn't have an equivilant of $REV. Its post-receive hook
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does, but I'm not sure if that's an appropriate hook for ikiwiki to be using
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for this. Switching existing wikis to use a different hook would be tricky..
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I've avoided part of the race; now the code does:
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1. Get commit info for HEAD commit.
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2. Extract file list from that.
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3. Extract sha1 of commit from it too.
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4. git diff sha1^ sha1
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Still seems like there can be a race if another commit comes in before step #1.
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In this case, two post-receive hooks could run at the same time, and both
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see the same sha1 as HEAD, so two diffs might be sent for second commit and no
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diff for the first commit.
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Ikiwiki's own locking prevents this from happenning if both commits are web
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edits. At least one of the two commits has to be a non-web commit.
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