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blog for the day

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Joey Hess 2012-06-19 18:32:30 -04:00
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Good news! My beta testers report that the new kqueue code works on OSX.
At least "works" as well as it does on Debian kFreeBSD. My crazy
development strategy of developing on Debian kFreeBSD while targeting Mac
OSX is vindicated. ;-)
So, I've been beating the kqueue code into shape for the last 12 hours,
minus a few hours sleep.
First, I noticed it was seeming to starve the other threads. I'm using
Haskell's non-threaded runtime, which does cooperative multitasking between
threads, and my C code was never returning to let the other threads run.
Changed that around, so the C code runs until SIGALARMed, and then that
thread calls `yield` before looping back into the C code. Wow, cooperative
multitasking.. I last dealt with that when programming for Windows 3.1!
(Should try to use Haskell's -threaded runtime sometime, but git-annex
doesn't work under it, and I have not tried to figure out why not.)
Then I made a [single commit](http://source.git-annex.branchable.com/?p=source.git;a=commitdiff;h=2bfcc0b09c5dd37c5e0ab65cb089232bfcc31934),
with no testing, in which I made the kqueue code maintain a cache of what
it expects in the directory tree, and use that to determine what files
changed how when a change is detected. Serious code. It worked on the
first go. If you were wondering why I'm writing in Haskell ... yeah,
that's why.
And I've continued to hammer on the kqueue code, making lots of little
fixes, and at this point it seems *almost* able to handle the changes I
throw at it. It does have one big remaining problem; kqueue doesn't tell me
when a writer closes a file, so it will sometimes miss adding files. To fix
this, I'm going to need to make it maintain a queue of new files, and
periodically check them, with `lsof`, to see when they're done being
written to, and add them to the annex. So while a file is being written
to, `git annex watch` will have to wake up every second or so, and run
`lsof` ... and it'll take it at least 1 second to notice a file's complete.
Not ideal, but the best that can be managed with kqueue.