[PATCH V6] dirstate: avoid a race with multiple commits in the same process

[Matt Mackall]

On Tue, 2011-03-22 at 18:03 +0100, Adrian Buehlmann wrote:
> On 2011-03-22 14:56, Matt Mackall wrote:
> > On Tue, 2011-03-22 at 09:13 +0100, Adrian Buehlmann wrote:
> >> On 2011-03-22 02:09, Greg Ward wrote:
> >>> On 21 March 2011, Adrian Buehlmann said:
> >>>>     def normal(self, f):
> >>>>         '''Mark a file normal and clean.'''
> >>>>         self._dirty = True
> >>>>         self._addpath(f)
> >>>>         s = os.lstat(self._join(f))
> >>>>         self._map[f] = ('n', s.st_mode, s.st_size, int(s.st_mtime))
> >>>>         if f in self._copymap:
> >>>>             del self._copymap[f]
> >>>>
> >>>>         # Right now, this file is clean: but if some code in this
> >>>>         # process modifies it without changing its size before the clock
> >>>>         # ticks over to the next second, then it won't be clean anymore.
> >>>>         # So make sure that status() will look harder at it.
> >>>>         self._lastnormal.add(f)
> >>>>
> >>>> Hmmm.
> >>>>
> >>>> local.status does a full compare for files that need to be looked into,
> >>>> which IIUC now includes the files in self._lastnormal (see
> >>>> dirstate.status() ).
> >>>
> >>> The set "files that need to be looked into" *may* include files in
> >>> self._lastnormal.  If one of them has changed size or mtime, it takes
> >>> the fast path to M status.
> >>
> >> Right. But it's only fast for the files which *have* been changed.
> > 
> > You can only take things out of the _lastnormal state when you know
> > their timestamp is older than the filesystem time. In particular, you
> > cannot do it when you've confirmed the contents are unchanged. Then
> > changes to a file -in process- may be missed.
> > 
> > But I think I see how to fix this: add _lastnormaltime. Whenever we call
> > normal(), we stat the file to get its timestamp and size for writing to
> > dirstate. Given that we're only worried about files in the current
> > second (or whatever the fs quantum is), if the current timestamp is
> > newer than the timestamp on the _lastnormal list, we can dump the
> > current list.
> > 
> > diff -r f52e5211450a mercurial/dirstate.py
> > --- a/mercurial/dirstate.py	Mon Mar 21 15:30:20 2011 -0500
> > +++ b/mercurial/dirstate.py	Tue Mar 22 08:54:48 2011 -0500
> > @@ -50,6 +50,7 @@
> >          self._dirty = False
> >          self._dirtypl = False
> >          self._lastnormal = set()        # files believed to be normal
> > +        self._lastnormaltime = None
> >          self._ui = ui
> >  
> >      @propertycache
> > @@ -290,6 +291,9 @@
> >          # process modifies it without changing its size before the clock
> >          # ticks over to the next second, then it won't be clean anymore.
> >          # So make sure that status() will look harder at it.
> > +        if self._lastnormaltime < s.st_mtime:
> > +            self._lastnormaltime = s.st_mtime
> > +            self._lastnormal = set()
> >          self._lastnormal.add(f)
> >  
> >      def normallookup(self, f):
> > 
> 
> Excellent idea.
> 
> I think we can even do != instead of <:

I don't this will work, we may mark a file normal that was last written
to hours ago. This will be the usual case with commit.

-- 
Mathematics is the supreme nostalgia of our time.