Re: [PATCH] build-sys: fix parallel builds w/setarch links

[Mike Frysinger <vapier@gentoo.org>]

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On 16 May 2015 14:50, Peter Cordes wrote:
> On Mon, May 11, 2015 at 10:05:28AM +0200, Karel Zak wrote:
> > On Sun, May 10, 2015 at 01:38:08PM -0700, Isaac Dunham wrote:
> > > On Tue, May 05, 2015 at 11:37:33AM +0100, Pádraig Brady wrote:
> > > > On 04/05/15 04:51, Mike Frysinger wrote:
> > > > > From: Mike Frysinger <vapier@chromium.org>
> > > > > 
> > > > > The symlink generation tries to write to the sys-utils/ subdir but does
> > > > > not make sure that dir exists.  This can sometimes lead to parallel build
> > > > > failures when building out-of-tree
> > > > 
> > > > >  $(SETARCH_MAN_LINKS):
> > > > > +	$(AM_V_at) test -d $(dir $@) || mkdir -p $(dir $@)
> > > > >  	$(AM_V_GEN)echo ".so man8/setarch.8" > $@
> > > > >  
> > > > >  install-exec-hook-setarch:
> > > > 
> > > > The `test -d ... ||` bit is racy and redundant I think
> > > 
> > > Racy, yes, but no more so than "mkdir -p $DIR && install $FILE $DIR":
> > > it's an inherent limitation of shell scripts.
> 
>  You mean racy as in multiple mkdir -p invocations could happen?  A C
> implementation could shorten the window for the race (because mkdir(2)
> would directly follow stat(2), rather than delayed by
> fork/exec/dynamic linker startup).  Or handle EEXISTS specially and
> test again for existance.  You could do most of that in shell, but it
> would make the code a mess.

shortening the window isn't interesting.  it's either race-free, or racy.  the 
incident rate is irrelevant.
-mike

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