On Nov 9, 3:31 am, shawnhco...@gmail.com (Shawn H Corey) wrote:
> Taylor, Andrew (ASPIRE) wrote:
> > Hello
>
> > I have a script that, much like the Little Old Lady who lived in a shoe,
> > has so many children it's not sure what to do.
>
> > Basically, the script does some stuff, then kicks off multiple copies of
> > an external process that all run in parallel. It then has to wait until
> > all of them have completed (successfully) then carry on with the next
> > bit.
>
> > What I've cobbled together so far (i.e. swiped of the web then
> > modified...)
>
> > use strict;
> > use warnings;
>
> > # Do some stuff here
>
> > for (my $i=1; $i <=$num_processes; $i++)
>
> for my $i ( 1 .. $num_processes )
>
> > {
> > defined(my $pid = fork) or die( "Cannot fork : $!\n");
>
> > # Put all the pids into an aray
> > if ($pid)
> > {
> > push @pids, $pid;
> > } else {
> > exec "external giggery pokery"
> > }
> > }
>
> > foreach my $child_pid (@pids)
> > {
> > waitpid($child_pid, 0);
>
> my $kid = waitpid($child_pid, 0);
>
> > unless( 0==$? )
> > {
> > die ("Oh No! An external process has failed!!\n");
> > }
>
> redo if $kid != $child_pid;
Hm, I'm not sure why you'd want to 'redo' in the case of a
blocking wait. As I read the docs, a blocking wait on a
specific pid returns only that pid if reaped normally or -1 if
there's no such pid (or that pid's been already reaped). In
either case, I'd think you'd just want to continue processing
the pid loop.
In contrast (at least on POSIX compliant OS's), a non-blocking
blocking wait with -1 rather than a specific pid could potentially
reap other pid's:
use POSIX ":sys_wait_h";
#...
do {
$kid = waitpid(-1, WNOHANG);
} while $kid > 0;
This might reap an extraneous process such as one launched via
backticks maybe in an forked pid for instance.
> On some systems, waitpid may return for any interrupt, not just when the
> child terminates.
Also the POSIX non-blocking wait has the advantage in that case by
providing macro's that can reveal some additional exit/termination
status:
use POSIX ":sys_wait_h";
...
$kid = waitpid( -1, WNOHANG);
print "$kid: signal termination" if WIFSIGNALED($?);
--
Charles DeRykus
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