release status - land new features before monday
robertc at robertcollins.net
Thu Apr 12 03:33:41 BST 2007
On Thu, 2007-04-12 at 11:08 +1000, Martin Pool wrote:
> On 4/12/07, John Arbash Meinel <john at arbash-meinel.com> wrote:
> > At this point, locking 'dirstate' is more of future proofing, because we
> > eventually will try to read just portions of the file, rather than
> > always reading the whole thing. And that starts to get dicey if the file
> > might be changing underneath you.
> Is it only future proofing? I mean, would there be any problems with
> two processes running the current code if there are no read locks?
Yes. We rewrite the file in place (no atomic replacement on windows), so
a anonymous reader can read an inconsistent file. We *had* bugs with
that before we added the read lock.
> The read lock has some other undesirable effects, like not being able
> to diff while a commit is pending.
> > So we could just make it so that on win98 we:
> > 1) Don't lock for reading
> > 2) Always read the whole file (disable partial reads).
It can still race I believe. In particular you can read less than a full
file if the writer shrinks the file.
> It would still be possible for a fast writer to update the whole file
> while the reader is partway through it, so it's not quite safe, at
> least in theory.
Definately, I've seen this happen.
GPG key available at: <http://www.robertcollins.net/keys.txt>.
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