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Plug race in parallel autotest.

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* lib/autotest/general.m4 (AT_INIT) <Fifo job dispatcher>: Track
two fds to fifo in parent, to avoid race where parent can see EOF
before child opens fifo.  Avoid any atomicity problems with tokens
larger than one byte.
* NEWS: Document the bug fix.

Signed-off-by: Eric Blake <eblake@redhat.com>
This commit is contained in:
Eric Blake 2010-07-20 21:14:14 -06:00
parent 82f7cdadbb
commit 97ecc667f7
3 changed files with 35 additions and 9 deletions
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10
ChangeLog
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@ -1,3 +1,13 @@
2010-07-20 Paul Eggert <eggert@cs.ucla.edu>
and Eric Blake <eblake@redhat.com>
Plug race in parallel autotest.
* lib/autotest/general.m4 (AT_INIT) <Fifo job dispatcher>: Track
two fds to fifo in parent, to avoid race where parent can see EOF
before child opens fifo. Avoid any atomicity problems with tokens
larger than one byte.
* NEWS: Document the bug fix.
2010-07-20 Eric Blake <eblake@redhat.com>
Another empty argument through expr workaround.

5
NEWS
View File

@ -20,6 +20,11 @@ GNU Autoconf NEWS - User visible changes.
** autoreconf passes warning flags to new enough versions of aclocal.
** Running an Autotest testsuite in parallel mode no longer triggers a
race condition that could cause the testsuite run to end early,
fixing a sporadic failure in autoconf's own testsuite. Bug present
since introduction of parallel tests in 2.63b.
* Major changes in Autoconf 2.66 (2010-07-02) [stable]
Released by Eric Blake, based on git versions 2.65.*.

29
lib/autotest/general.m4
View File

@ -959,7 +959,10 @@ export PATH
# Setting up the FDs.
m4_define([AS_MESSAGE_LOG_FD], [5])
m4_define([AT_JOB_FIFO_FD], [6])
dnl The parent needs two fds to the same fifo, otherwise, there is a race
dnl where the parent can read the fifo before a child opens it for writing
m4_define([AT_JOB_FIFO_IN_FD], [6])
m4_define([AT_JOB_FIFO_OUT_FD], [7])
[#] AS_MESSAGE_LOG_FD is the log file. Not to be overwritten if `-d'.
if $at_debug_p; then
at_suite_log=/dev/null
@ -1376,7 +1379,14 @@ dnl avoid all the status output by the shell.
(
# Start one test group.
$at_job_control_off
exec AT_JOB_FIFO_FD>"$at_job_fifo"
dnl First child must open the fifo to avoid blocking parent; all other
dnl children inherit it already opened from the parent.
if $at_first; then
exec AT_JOB_FIFO_OUT_FD>"$at_job_fifo"
else
dnl Children do not need parent's copy of fifo.
exec AT_JOB_FIFO_IN_FD<&-
fi
dnl When a child receives PIPE, be sure to write back the token,
dnl so the master does not hang waiting for it.
dnl errexit and xtrace should not be set in this shell instance,
@ -1386,7 +1396,7 @@ dnl optimize away the _AT_CHECK subshell, so normalize here.
dnl Ignore PIPE signals that stem from writing back the token.
trap "" PIPE
echo stop > "$at_stop_file"
echo token >&AT_JOB_FIFO_FD
echo >&AT_JOB_FIFO_OUT_FD
dnl Do not reraise the default PIPE handler.
dnl It wreaks havoc with ksh, see above.
dnl trap - 13
@ -1395,26 +1405,27 @@ dnl kill -13 $$
at_fn_group_prepare
if cd "$at_group_dir" &&
at_fn_test $at_group &&
. "$at_test_source" # AT_JOB_FIFO_FD>&-
. "$at_test_source" [#] AT_JOB_FIFO_OUT_FD>&-
then :; else
AS_WARN([unable to parse test group: $at_group])
at_failed=:
fi
at_fn_group_postprocess
echo token >&AT_JOB_FIFO_FD
echo >&AT_JOB_FIFO_OUT_FD
) &
$at_job_control_off
if $at_first; then
at_first=false
exec AT_JOB_FIFO_FD<"$at_job_fifo"
exec AT_JOB_FIFO_IN_FD<"$at_job_fifo" AT_JOB_FIFO_OUT_FD>"$at_job_fifo"
fi
shift # Consume one token.
if test $[@%:@] -gt 0; then :; else
read at_token <&AT_JOB_FIFO_FD || break
read at_token <&AT_JOB_FIFO_IN_FD || break
set x $[*]
fi
test -f "$at_stop_file" && break
done
exec AT_JOB_FIFO_OUT_FD>&-
# Read back the remaining ($at_jobs - 1) tokens.
set X $at_joblist
shift
@ -1423,9 +1434,9 @@ dnl kill -13 $$
for at_job
do
read at_token
done <&AT_JOB_FIFO_FD
done <&AT_JOB_FIFO_IN_FD
fi
exec AT_JOB_FIFO_FD<&-
exec AT_JOB_FIFO_IN_FD<&-
wait
else
# Run serially, avoid forks and other potential surprises.