Avoid non-portable signal(SIGCHLD, SIG_IGN)

[Joerg Wunsch]

As Alexandre Julliard wrote:

> The fact that the macro exists doesn't mean it works. Most Linux
> kernels don't support SA_NOCLDWAIT, even though the symbol may be
> defined in the headers.

That sounds to be a very stupid mistake to me.  Why would one define
something one doesn't support?  But OK, that's nothing we can change.

> I don't have the Posix standard, but at least according to the
> single Unix spec using SIG_IGN is just as standard as SA_NOCLDWAIT,
> and a quick grep of the FreeBSD sources seems to indicate that it
> should work. Did I miss something?

signal() is not part of Posix at all, IIRC.  Sure, SIG_IGN has always
been defined, but its effect on SIGCHLD didn't used to be defined.
When i implemented the FreeBSD SA_NOCLDWAIT feature, i purposely
decided to not also implement the SIG_IGN irregularity (SIG_IGN means
that the /signal/ is being ignored, but never implied any other
side-effect in the past), to remain backwards compatible with the BSD
behaviour.

It's still that way, see the following short test program:

j at uriah 720% cat foo.c
#include <signal.h>
#include <unistd.h>
#include <stdlib.h>

void
createchild(void)
{
        if (fork() == 0) {
                exit(0);
        }
}

int
main(void)
{
        createchild();
        createchild();
        createchild();
        sleep(1);
        system("ps");
        sleep(2);
        return 0;
}
j at uriah 721% make foo
cc -O -pipe  foo.c  -o foo
j at uriah 722% ./foo
  PID  TT  STAT      TIME COMMAND
...
    0  p3  ZW+    0:00.00  (foo)
    0  p3  ZW+    0:00.00  (foo)
    0  p3  ZW+    0:00.00  (foo)
  992  p3  Ss     0:02.13 -tcsh (tcsh)
12287  p3  S+     0:00.00 ./foo
12291  p3  S+     0:00.00 sh -c ps
12292  p3  R+     0:00.00 ps
...

Of course, now that i see that SUSP indeed standardized this oddness,
i might change my opinion.  Anyway, as demonstrated above,
signal(SIGCHLD, SIG_IGN) doesn't work on FreeBSD the way you would
expect it to work.  So Gerald, please at least integrate the patch
into the FreeBSD port.

-- 
cheers, J"org               .-.-.   --... ...--   -.. .  DL8DTL

http://www.sax.de/~joerg/                        NIC: JW11-RIPE
Never trust an operating system you don't have sources for. ;-)