reaper subroutines

jalebie has asked for the wisdom of the Perl Monks concerning the following question:

Hi, I am having trouble with the following piece of code in my reaper subroutine, I am trying to keep a track of the number of child processes that have finished.

use POSIX "sys_wait_h";
use POSIX "signal_h";
      ...
      ...
      ...
sub reaper {
    my $process_id = waitpid(-1,&WNOHANG);
    if (WIFEXITED($?)) {
        $process_count--;
    }
}

$SIG{CHLD} = \&reaper;
[download]

and i get the follwong error

Argument "CHLD" isn't numeric in entersub at /usr/bin/perl/perl5.005/lib/POSIX.pm line 207.

please help
Waris

Comment on reaper subroutines Download Code

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(tye)Re: reaper subroutines by tye (Sage) on Aug 23, 2001 at 21:44 UTC
Change `&WNOHANG` to `WNOHANG()` or `WNOHANG` and then yell at whoever taught you to use `&NAME` for constants in hopes that this problematic but still common practice can be stomped out. FYI, the reason you get this warning is that your `sub reaper` gets called with the name of the signal passed in to it and calling a subroutine (and constants from Perl modules are usually subroutines) with `&` and without parens means that the current value of `@_` is reused as the arguments to that subroutine. So you end up doing the equivalent of `WNOHANG(@_)` which, in your case, is similar to `WNOHANG("CHLD")`. Finally, for obscure reasons, the example code for implementing constants in XS modules, allows these so-called "constants" to take an optional numeric argument. But "CHLD" isn't numeric, hence the warning. - tye (but my friends call me "Tye")	[reply] [d/l] [select]
Re: (tye)Re: reaper subroutines by chromatic (Archbishop) on Aug 24, 2001 at 02:27 UTC
Unfortunately, this culprit looks like the fine manual. The example in perlfunc (5.6.0) reads: `use POSIX ":sys_wait_h"; #... do { $kid = waitpid(-1,&WNOHANG); } until $kid == -1;` [download] Worse yet, the docs for POSIX in 5.7.2 give this example: `$pid = POSIX::waitpid( -1, &POSIX::WNOHANG ); print "status = ", ($? / 256), "\n";` [download] You want to submit a doc patch to p5p or should I? :)	[reply] [d/l] [select]