[Quilt-dev] Race in test suite (faildiff.test)

[Jean Delvare]

Hi Andreas,

Once in a while, the quilt test suite fails with:

[faildiff.test]
[1] $ mkdir patches -- ok
[3] $ quilt new test.diff -- ok
[6] $ cat > test.txt -- ok
[8] $ quilt add test.txt -- ok
[13] $ chmod -r test.txt -- ok
[15] $ quilt refresh -- ok
[18] $ echo 1 -- ok
[21] $ chmod +r test.txt -- ok
[25] $ printf "\\002\\000\\001" > test.bin -- ok
[26] $ quilt add test.bin -- ok
[29] $ printf "\\003\\000\\001" > test.bin -- ok
[30] $ quilt diff -pab --no-index -- failed
Diff failed on file 'test.bin', aborting !~ (Files|Binary files) a/test\.bin 
and b/test\.bin differ
Binary files a/test.bin and b/test.bin differ != Diff failed on file 
'test.bin', aborting
[33] $ echo 1 -- ok
[36] $ quilt refresh -- ok
[38] $ echo 1 -- ok
15 commands (14 passed, 1 failed)
Makefile:410: recipe for target 'test/.faildiff.ok' failed
make: *** [test/.faildiff.ok] Error 1

The reason is that the 2 messages are not printed in the same order as
expected. Looking at the code, I can't explain how this can possibly
happen. "Binary files ..." is printed first in the code, and the
subprocess which prints it is already gone by the time we reach the
line which prints "Diff failed ...". It has to be, because we check its
status code before printing "Diff failed ...".

The inversion is very rare, the test can succeed hundred or even
thousand times before if fails again. I'm using the following command
to reproduce the error:

$ n=0 ; while make check-faildiff ; do let n=n+1 ; echo $n ; rm 
test/.faildiff.ok ; done

Do you have any idea how this can happen? Am I missing something, or
could this be a bug in bash? I tried a few tricks (stdbuf, wait...) but
nothing seems to solve the problem. If you (or anyone reading this)
have any suggestion, that would be very welcome.

Thanks,
-- 
Jean Delvare
SUSE L3 Support