[rfc] [patch] another small cleanup

[John Arbash Meinel]

Denys Duchier wrote:
> Another small cleanup from my bzr.cleanup branch at:
> 
>              http://delta.univ-orleans.fr/~duchier/bzr/bzr.cleanup/
> 
> ------------------------------------------------------------
> revno: 1501
> committer: Denys Duchier <denys.duchier at mozart-oz.org>
> branch nick: bzr.cleanup
> timestamp: Wed 2006-01-11 20:58:59 +0100
> message:
>   hashcache: new constants and improved comment
> 
> 
> 
> 
> ------------------------------------------------------------------------
> 
> === modified file 'bzrlib/hashcache.py'
> --- bzrlib/hashcache.py	
> +++ bzrlib/hashcache.py	
> @@ -38,6 +38,8 @@
>  from bzrlib.errors import BzrError
>  
>  
> +FP_MTIME_COLUMN = 1
> +FP_CTIME_COLUMN = 2
>  FP_MODE_COLUMN = 5
>  
>  def _fingerprint(abspath):
> @@ -175,10 +177,18 @@
>              raise BzrError("file %r: unknown file stat mode: %o"%(abspath,mode))
>  
>          now = int(time.time())
> -        if file_fp[1] >= now or file_fp[2] >= now:
> +        if file_fp[FP_MTIME_COLUMN] >= now or file_fp[FP_CTIME_COLUMN] >= now:
>              # changed too recently; can't be cached.  we can
>              # return the result and it could possibly be cached
>              # next time.
> +            #
> +            # the point is that we only want to cache when we are sure that any
> +            # subsequent modifications of the file can be detected.  If a
> +            # modification neither changes the inode, the device, the size, nor
> +            # the mode, then we can only distinguish it by time; therefore we
> +            # need to let sufficient time elapse before we may cache this entry
> +            # again.  If we didn't do this, then, for example, a very quick 1
> +            # byte replacement in the file might go undetected.
>              self.danger_count += 1 
>              if cache_fp:
>                  self.removed_count += 1
> 
> 
> 
> ------------------------------------------------------------------------
> 
> 
> 
> Cheers,
> 
> --Denys

+1 from me. (not merged yet)

John
=:->

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