cc: [email protected]
Subject: Re: [ast-users] Trouble with .sh.sig and SIGCHLD traps
--------
> I found this very cool but undocumented (why?) feature that you can
> find the sender of a signal and pass a value (for realtime signals):
> ~/bin/ksh -c 'compound pc ; trap "pc.value=\${.sh.sig.value}
> pc.pid=\${.sh.sig.pid}" RTMIN ; integer thispid=$$ ; kill -q 16#23456
> -RTMIN $thispid & ; wait ; printf "%s\n" "${pc}"'
> (
> pid=984
> value=16#23456
> )
>
> Now I thought this could be used create scripts which handle SIGCHLD
> in an event-driven manner, but the concept doesn't work for SIGCHLD
> traps:
> ~/bin/ksh -c 'compound pc=( integer value=-1 pid=-1 ) ; trap
> "pc.value=\${.sh.sig.value} pc.pid=\${.sh.sig.pid} ; print trapCHLD"
> CHLD ; integer thispid=$$ ; sleep 2 & ; wait ; printf "%s\n" "${pc}"'
> trapCHLD
> (
> typeset -l -i pid=0
> typeset -l -i value=0
> )
>
> Why does that happen?
>
This feature is undocumented because it is incomplete.
However, for the SIGCHLD trap, if it were implemented, it would show
who sent the signal, not the process that terminated. A user could
send SIGINT to another process.
However, currently, $! is set to the pid of the terminated process
that triggered the SIGCHLD trap.
David Korn
[email protected]
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