Fix test failures caused by slow SIGCHLD handling (#922)

When I run the ksh test case, I occasionally encounter the error

  sigchld.sh[77]: FAIL: SIGCHLD trap queueing failed -- expected
  'running=0 maxrunning=4', got 'running=1 maxrunning=4'

as described in:
#344 (comment)

I tried to simplify the reproduction process

  #!/bin/ksh
  integer count=1
  while true
  do
      jobmax=4
      got=$(ksh -c '
          JOBMAX='$jobmax' JOBCOUNT=$(('$jobmax'*2))
          integer running=0 maxrunning=0
          trap "((running--))" CHLD
          for ((i=0; i<JOBCOUNT; i++))
          do  sleep 1 &
              if   ((++running > maxrunning))
              then ((maxrunning=running))
              fi
          done
          wait
          sleep 1
          print running=$running maxrunning=$maxrunning
      ')
      exp='running=0 maxrunning='$jobmax
      echo "when $count, expected '$exp', got '$got'"
      ((count++))
      [[ $got == $exp ]] || exit 1
  done

Without adding 'sleep', the script encounters the same error after
looping a few hundred times. With 'sleep' added, I have run it tens
of thousands of times in my local environment without seeing the
error.

The completion of 'wait' does not necessarily mean that the trap
has finished handling the SIGCHLD signal. Therefore, this error is
not a design flaw in ksh itself, but rather an issue with the test
case design. Adding an appropriate delay can prevent the test case
from failing due to this error.

src/cmd/ksh93/tests/sigchld.sh:
- The delay logic was modified to wait 0.1 seconds each time and
  check whether running is 0, with a maximum total delay of 1
  second.
  At least in my local environment, a 1‑second delay is sufficient
  to ensure that this test case passes.

Author: YoruStar

COPYRIGHT

@@ -27,6 +27,7 @@ ksh 93u+m general copyright notice
 #                 Harald van Dijk <harald@gigawatt.nl>                 #
 #             dnewhall <dnewhall@users.noreply.github.com>             #
 #                   Chase <nicetrynsa@protonmail.ch>                   #
+#                     YoruStar <524413304@qq.com>                      #
 #                      Trey Valenta <t@trey.net>                       #
 #  Sterling Jensen <5555776+sterlingjensen@users.noreply.github.com>   #
 #            SHIMIZU Akifumi <shimizu.akifumi@fujitsu.com>             #

src/cmd/ksh93/tests/sigchld.sh

@@ -2,7 +2,7 @@
 #                                                                      #
 #               This software is part of the ast package               #
 #          Copyright (c) 1982-2012 AT&T Intellectual Property          #
-#          Copyright (c) 2020-2024 Contributors to ksh 93u+m           #
+#          Copyright (c) 2020-2026 Contributors to ksh 93u+m           #
 #                      and is licensed under the                       #
 #                 Eclipse Public License, Version 2.0                  #
 #                                                                      #
@@ -13,6 +13,7 @@
 #                  David Korn <dgk@research.att.com>                   #
 #                  Martijn Dekker <martijn@inlv.org>                   #
 #            Johnothan King <johnothanking@protonmail.com>             #
+#                     YoruStar <524413304@qq.com>                      #
 #                                                                      #
 ########################################################################
 
@@ -71,6 +72,12 @@ then
 			fi
 		done
 		wait
+		integer tries=0, maxtries=10
+		while ((running > 0 && tries < maxtries))
+		do
+			sleep 0.1
+			((tries++))
+		done
 		print running=$running maxrunning=$maxrunning
 	')
 	exp='running=0 maxrunning='$jobmax