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Re: Child process inter communication

by zentara (Archbishop)
on Jun 13, 2017 at 13:11 UTC ( #1192681=note: print w/replies, xml ) Need Help??


in reply to Child process inter communication

Hi, these following codes have been posted before in some lost node numbers. But here is the way to do it: Also see Fork and wait question. You can setup 2 way pipes too, so you can have bi-directional communication between parent and child.
#!/usr/bin/perl use warnings; use strict; #piping all child output to parent # by Zaxo of perlmonks # we'll define some subroutiness to act as children # and open a single pipe. my @kids = ( sub { print "First!", $/; }, sub { print "Second!", $/; }, sub { print "Third!", $/; }, ); pipe my ( $in, $out ); # Now we start breeding children. Each will close the $in handle, # select the $out handle as the default, set up autoflush on it, # and then call their sub. We definitely need to prevent zombies, # since the kids will all finish before the parent does, so we # start by declaring a hash where we will keep their pid's. my %kid; for (@kids) { my $cpid = fork; defined $cpid or warn("Couldn't fork"), next; $cpid or do { # child close $in or die $!; select $out; $| = 1; $_->(); exit 0; }; $kid{$cpid} = undef; } # The select statement is the one-arg kind, which windows should # handle ok. Back in the parent, now, we have an unwanted $out handle, # a single $in handle that the kids are all fighting to talk on, and # a hash to remind us of the kids' names. Wrapping up, we close $out, # listen to the kids in turn, decorate their messages to show # who's repeating them, and finally call wait enough times to # bury them all safely. We must be careful not to die before that. close $out or warn $!; s/.$/??? says the child/, print while <$in>; delete $kid{ +wait } while %kid; # Many-to-one pipes like this will keep their messages' integrity # in flush-sized chunks. So long as they are shorter than than # an I/O buffer and end with $/, they will be read as distinct. # You may want to have the kids tag their messages to # identify the source. # I've tested this on Windows XP and Linux. It works on both.
or simpler, pipe all output to parent
#!/usr/bin/perl use strict; use warnings; my $pid = open(CHILD, "-|"); if ($pid) { # parent print "parent got:\n"; print while(<CHILD>); close CHILD; # this waits on child } elsif ($pid == 0) { # child print "kid here!\n"; exec '/bin/date' or die "Can't exec date $!\n"; } else { die "fork error: $!\n"; }

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