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Date: Mon, 13 Oct 2014 14:59:03 +0200
From: Stefan Esser <se@freebsd.org>
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To: Matthias Apitz <guru@unixarea.de>
Subject: Re: gmake && file time precision of 1 second
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Am 13.10.2014 um 11:20 schrieb Matthias Apitz:
> 
> Hello,
> 
> I have a large project where a shell script fires up
> gmake runs in subdirs as:
> 
> for dir in src norm print ....; do 
>    cd $dir
>    gmake
>    cd ..
> done
> 
> in each subdir *.c are compiled to *.o and the resulting *.o are ar'ed
> into all the same lib.a; based on normal Makefile rules like:
> 
> SRCS = f1.c f2.c
> OBJS = $(SRCS:.c=.o)
> 
> .c.o:
> 	$(CC) -c ... $*.c
> 
> lib.a:: $(OBJS)
> 	$(AR) $@ $(OBJS)
> 
> 
> after moving to a faster server it turned out that gmake sometimes forget
> to ar the *.o into the lib; I investigated it and it turned out that the
> *.o files have the same modification time (in seconds) as the target
> lib.a (which was produced/updated in the last directory worked on) and
> gmake thinks that the lib.a is uptodate.
> 
> Any idea how to address this in the Makefiles?
> 
> Well I could place (and it works) a 'sleep 1' into the loop, but I think
> that there is some better way.

Could this be a solutionn for you:

$ sysctl -d vfs.timestamp_precision
vfs.timestamp_precision: File timestamp precision (0: seconds, 1: sec +
ns accurate to 1/HZ, 2: sec + ns truncated to ms, 3+: sec + ns (max.
precision))

Beware: This is a global variable, higher resolution timestamps are
not supported on all filesystems, and not all programs check for the
sub-second part of the timestamp value ...

Regards, STefan