[PATCH 1 of 4 STABLE] dirstate: delay writing out to ensure timestamp of each entries explicitly

[FUJIWARA Katsunori]

At Wed, 23 Jul 2014 00:15:24 +0900,
FUJIWARA Katsunori wrote:
> 
> # HG changeset patch
> # User FUJIWARA Katsunori <foozy at lares.dti.ne.jp>
> # Date 1406041170 -32400
> #      Tue Jul 22 23:59:30 2014 +0900
> # Branch stable
> # Node ID 89b809fa6cefb56d10ac0ce68dfdddadc896af20
> # Parent  a5168eb9b2bc488f42809872d22321a9825bc738
> dirstate: delay writing out to ensure timestamp of each entries explicitly

This series can fix timing critical issues like below:

    http://www.selenic.com/pipermail/mercurial-devel/2013-May/051225.html

> Even though "dirstate.write()" is invoked explicitly after "normal"
> invocations, timestamp field of entries may be still "unset" in the
> "dirstate" file itself , because "pack_dirstate" drops it when it is
> equal to the timestamp of "dirstate" file itself.
> 
> This can avoid overlooking modification of files, which are updated at
> same time in the second. But on the other hand, this may hide timing
> critical problems.
> 
> For example, incorrect "normal"-ing (or lack of "normallookup"-ing on
> the already "normal"-ed entry) is visible only when:
> 
>   - the target file is modified in the working directory at T1, and
>   - "dirstate" file is written out at T2 (!= T1)
> 
> Otherwise, T1 is dropped by "pack_dirstate" in "dirstate.write()"
> invocation, and "unset" is stored into "dirstate" file.
> 
> It often fails to reproduce problems from incorrect "normal"-ing by
> Mercurial testset, because automated actions in the small repository
> almost always causes that T1 and T2 are same.
> 
> This patch adds the debug feature to delay writing out to ensure
> timestamp of each entries explicitly.
> 
> This feature is used to make timing critical "dirstate" problems
> reproducable in subsequent patches.
> 
> diff --git a/mercurial/dirstate.py b/mercurial/dirstate.py
> --- a/mercurial/dirstate.py
> +++ b/mercurial/dirstate.py
> @@ -504,6 +504,14 @@
>      def write(self):
>          if not self._dirty:
>              return
> +
> +        # enough 'delaywrite' prevents 'pack_dirstate' from dropping
> +        # timestamp of each entries in dirstate, because of 'now > mtime'
> +        delaywrite = self._ui.configint('debug', 'dirstate.delaywrite', 0)
> +        if delaywrite:
> +            import time # to avoid useless import
> +            time.sleep(delaywrite)
> +
>          st = self._opener("dirstate", "w", atomictemp=True)
>          # use the modification time of the newly created temporary file as the
>          # filesystem's notion of 'now'
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----------------------------------------------------------------------
[FUJIWARA Katsunori]                             foozy at lares.dti.ne.jp