trap not work in program with a subshell environment

From: Michael Wang (mwang@unixlabplus.com)
Date: 04/24/03 

From: mwang@unixlabplus.com (Michael Wang)
Date: Wed, 23 Apr 2003 22:26:27 GMT

Here is my sample program: 

--
#!/usr/dt/bin/dtksh
{
{
{
(
    PID= unset PID; (( PID = 0 ))
    function handle_signal {
      (( PID == 0 )) || {
        kill $PID
        print "killed $PID."
      }
      print "inside trap."
      exit 1
    }
    trap handle_signal INT TERM
    /bin/sleep 1200 &
    PID=$!
    wait $PID
)
print "exit_code=$?"
} 9>&- | tee -a /dev/null >&9
} 2>&1 | tee -a /dev/null >&2
} 9>&1
print "I am here."
--
And here is the process tree. Please note the program
"1.ksh" appears twice in the process tree.
      7204  /usr/dt/bin/dtksh ./1.ksh
        7206  tee -a /dev/null
        7205  tee -a /dev/null
          7207  /usr/dt/bin/dtksh ./1.ksh
            7208  /bin/sleep 1200
If I kill the second "1.ksh" (PID: 7207), then I get the intended
behavior. However if I kill the first "1.ksh" (PID: 7204), then
the program terminates without trapping.
And this is the problem, because the first process is the process that
will be killed by the parent process, which does not know the second
process.
If I move the function handle_signal, and the trap outside the subshell
environment (...):
--
#!/usr/dt/bin/dtksh
    PID= unset PID; (( PID = 0 ))
    function handle_signal {
      (( PID == 0 )) || {
        kill $PID
        print "killed $PID."
      }
      print "inside trap."
      exit 1
    }
    trap handle_signal INT TERM
{
{
{
(
    /bin/sleep 1200 &
    PID=$!
    wait $PID
)
print "exit_code=$?"
} 9>&- | tee -a /dev/null >&9
} 2>&1 | tee -a /dev/null >&2
} 9>&1
print "I am here."
--
and I got a process tree:
      8947  /usr/dt/bin/dtksh ./2.ksh
        8950  tee -a /dev/null
        8948  tee -a /dev/null
          8949  /usr/dt/bin/dtksh ./2.ksh
            8951  /bin/sleep 1200
The problem is no matter which process (8947 or 8949) I kill,
the program does not terminate.
However if I get rid of the complicated subshell environment:
--
#!/usr/dt/bin/dtksh
    PID= unset PID; (( PID = 0 ))
    function handle_signal {
      (( PID == 0 )) || {
        kill $PID
        print "killed $PID."
      }
      print "inside trap."
      exit 1
    }
    trap handle_signal INT TERM
    /bin/sleep 1200 &
    PID=$!
    wait $PID
print "I am here."
--
I get a process tree shown below. Please note 
the process named "3.ksh" appear only once.
      9417  /usr/dt/bin/dtksh ./3.ksh
        9418  /bin/sleep 1200
And if I kill the process, it gives the expected behaviour.
But the problem is I need the complicated subshell environment
so that stdout and stderr are duplicated to a file. And my goal
is with this subshell environment, trap is used when I kill the
first process, and ideally trap is also used when I kill the
second process, or any process in the tree, as I can not predict
how user uses "ps", "grep", and "kill".
Thanks.
-- 
Michael Wang * http://www.unixlabplus.com/ * mwang@unixlabplus.com

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