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Postings from February 2007
On Feb 05 2007, Alan Ferrency wrote:
> - According to the Fedora man page for sigaction(), POSIX specification
> (B.3.3.1.3) disallows setting SIGCHLD to SIG_IGN at all. (I can't seem
> to find the actual section text, unfortunately.) From a Perl
> perspective, does this mean it's illegal for Perl to set SIGCHLD to
> SIG_IGN, or that it's illegal for me to set $SIG{CHLD} = 'IGNORE' in
> my Perl code?
From my Ubuntu manpage for sigaction(2):
POSIX.1-1990 disallowed setting the action for SIGCHLD to SIG_IGN.
POSIX.1-2001 allows this possibility, so that ignoring SIGCHLD can be
used to prevent the creation of zombies (see wait(2)). Nevertheless,
the historical BSD and System V behaviours for ignoring SIGCHLD differ,
so that the only completely portable method of ensuring that terminated
children do not become zombies is to catch the SIGCHLD signal and per‐
form a wait(2) or similar.
Regardless, I think Perl's wait() can only be expected to call the
OS's wait(2). If there are any POSIX.1-1990 conformant systems out there
then I'd expect them to balk at setting SIGCHLD to SIG_IGN with
sigaction(). And by extension, Perl should fail when setting
$SIG{CHLD} = 'IGNORE' on such a system. If not, please file a bug report.
:-)
As long as Perl is using the underlying system calls, it has some hope of
meeting the standards of the OS it's running on. I don't think it's
Perl's place to try to be the One True Standard, certainly not for
low-level system calls.
--
Rick Delaney
rick@bort.ca
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