Re: testsuite failure - 193 parallel execution

[Paul Eggert]

On 07/20/10 14:55, Eric Blake wrote:
> the '|| break' that you are deleting is there in case
> something kills off the child and it never gets around to writing a
> token, at which point we've now put the parent into an inf-loop

OK, though if the child is killed off arbitrarily then we're helpless
(the first child could get killed before it opens the fifo, which
means the parent will wait forever trying to open the fifo); but I
see what you mean: that patch made infinite loops too likely in
the presence of arbitrary child failure.

How about this idea instead: have the parent open the fifo for
output, except do this _after_ the first job has started (so
we know we can open the fifo without hanging, under the same
assumptions as before).  That way, the race condition is closed.
Something like this:

--- general.m4  2010-07-20 15:23:26.823143793 -0700
+++ /tmp/general.m4     2010-07-20 15:37:36.719138878 -0700
@@ -960,6 +960,7 @@ export PATH
 # Setting up the FDs.
 m4_define([AS_MESSAGE_LOG_FD], [5])
 m4_define([AT_JOB_FIFO_FD], [6])
+m4_define([AT_JOB_OUTFIFO_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 +1377,9 @@ dnl avoid all the status output by the s
     (
       # Start one test group.
       $at_job_control_off
-      exec AT_JOB_FIFO_FD>"$at_job_fifo"
+      if $at_first; then
+       exec AT_JOB_OUTFIFO_FD>"$at_job_fifo"
+      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 +1389,7 @@ dnl optimize away the _AT_CHECK subshell
 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_OUTFIFO_FD
 dnl Do not reraise the default PIPE handler.
 dnl It wreaks havoc with ksh, see above.
 dnl        trap - 13
@@ -1395,18 +1398,19 @@ dnl         kill -13 $$
       at_fn_group_prepare
       if cd "$at_group_dir" &&
         at_fn_test $at_group &&
-        . "$at_test_source" # AT_JOB_FIFO_FD>&-
+        . "$at_test_source" # AT_JOB_OUTFIFO_FD>&-
       then :; else
        AS_WARN([unable to parse test group: $at_group])
        at_failed=:
       fi
       at_fn_group_postprocess
-      echo token >&AT_JOB_FIFO_FD
+      echo >&AT_JOB_OUTFIFO_FD
     ) &
     $at_job_control_off
     if $at_first; then
       at_first=false
       exec AT_JOB_FIFO_FD<"$at_job_fifo"
+      exec AT_JOB_OUTFIFO_FD>"$at_job_fifo"
     fi
     shift # Consume one token.
     if test address@hidden:@] -gt 0; then :; else
@@ -1415,6 +1419,7 @@ dnl           kill -13 $$
     fi
     test -f "$at_stop_file" && break
   done
+  exec AT_JOB_OUTFIFO_FD<&-
   # Read back the remaining ($at_jobs - 1) tokens.
   set X $at_joblist
   shift