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Date: Sun, 19 Dec 2010 14:37:00 -0000
From: Ralf Wildenhues <Ralf.Wildenhues@gmx.de>
To: "H.J. Lu" <hjl.tools@gmail.com>
Cc: binutils@sourceware.org
Subject: Re: PATCH: PR binutils/12283: bfd/doc doesn't support parallel build
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* Ralf Wildenhues wrote on Thu, Dec 02, 2010 at 07:32:31PM CET:
> > > * H.J. Lu wrote on Thu, Dec 02, 2010 at 07:16:07PM CET:
> > > > Failure is very random. There is a race condition. "make -j8" on a 16core
> > > > machine can start making $(MKDOC) at the same time. How can move-if-change
> > > > be 100% atomic?

> > Ahh, move-if-change is broken: it doesn't ignore mv -f failure when the
> > target is equal.  Let's fix move-if-change.
> 
> Does this alternative (untested) patch fix the race?

Have you had a chance to try this out?

Thanks,
Ralf

> ChangeLog:
> 2010-12-02  Ralf Wildenhues  <Ralf.Wildenhues@gmx.de>
> 
> 	PR binutils/12283
> 	* move-if-change: Ignore failure of 'mv -f' if the destination
> 	is equal to the source afterwards.
> 
> diff --git a/move-if-change b/move-if-change
> index ff74a55..1d2dd09 100755
> --- a/move-if-change
> +++ b/move-if-change
> @@ -4,6 +4,8 @@
>  
>  usage="$0: usage: $0 SOURCE DEST"
>  
> +cmpprog=${CMPPROG-cmp}
> +
>  case $# in
>  2) ;;
>  *) echo "$usage" >&2; exit 1;;
> @@ -18,5 +20,8 @@ done
>  if test -r "$2" && cmp -s "$1" "$2"; then
>    rm -f "$1"
>  else
> -  mv -f "$1" "$2"
> +  if mv -f "$1" "$2"; then :; else
> +    # Ignore failure due to a concurrent move-if-change.
> +    $cmpprog "$1" "$2" >/dev/null 2>&1
> +  fi
>  fi