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I have a piece of code and I really don't understand what's
happening...

The code:

#! /bin/perl
# Forking out a series of processes which may take
# a while to run. System waits for any SIGCHILD signal to be
# received back so that it can get the faster ones
# finalised quickly! Once a SIGCHILD signal is received back
# it accounts for it in an array

use strict;
use warnings;
use POSIX ":sys_wait_h";


my @waitlist = (20,10,35);
$SIG{CHLD} = \&REAPER;
my $start = localtime();
print "Started $start\n";
my $parent = $$;
my $child=0;
my @kids=();
my $waitedpid;
my $gotone;
my $finished_child;
my $pid;
my $child_pid;

foreach $child (@waitlist) {
unless ($pid = fork()) {
# Child process
sleep $child;
print "I am the kid # $child and I am completed\n";
exit();
}
# Parent process - loop to start others
push @kids, $pid;
}
print "The kids array\n";
foreach (@kids){
print $_,"\n";
}

print "Parent continues now...\n";
# Parent - wait for returned data
while (&sum_pids > 0) {
print "sum_pids=",&sum_pids,"\n";
while (! $gotone){
sleep 1;
print "Slept 1\n";
}
$gotone=0;
print "finished_child=$finished_child","\n";
foreach (@kids){
if ($finished_child=$_){
print "\$finished_child=",$finished_child,"\n";
print "\$_=",$_,"\n";
print "I am the parent and process $_ finished!!!\n";
$_=0;
}
}
}

print "And in the end sum_pids=",&sum_pids,"\n";
print "Completed!!!\n";


sub REAPER {
if (($finished_child = waitpid(-1, &WNOHANG)) > 0){
$gotone = 1;
}
# $SIG{CHLD} =\&REAPER;
}


sub sum_pids{
my $temp;

foreach $child_pid (@kids){
$temp+=$child_pid;
}
$temp;
}




The output:
Started Fri Jan 12 11:03:53 2007
I am the kid # 10 and I am completed
The kids array
5332
5333
5335
Parent continues now...
sum_pids=16000
Slept 1
Slept 1
Slept 1
Slept 1
Slept 1
Slept 1
Slept 1
Slept 1
Slept 1
Slept 1
finished_child=5333
$finished_child=5332
$_=5332
I am the parent and process 5332 finished!!!
$finished_child=5333
$_=5333
I am the parent and process 5333 finished!!!
$finished_child=5335
$_=5335
I am the parent and process 5335 finished!!!
And in the end sum_pids=0
Completed!!!
I am the kid # 20 and I am completed
I am the kid # 35 and I am completed



The questions: How is it possible to display only once
"finished_child=5333" and then to display $finished_child three times?
That would mean that it's catching only one SIGCHLD but somehow it's
executing that "if ($finished_child) three times. How come?


Thanks
trxrse

trxrse <> wrote in comp.lang.perl.misc:
> I have a piece of code and I really don't understand what's
> happening...

Nor do I, finding your code a bit hard to follow. I noticed

if ($finished_child=$_){

in your code. That should almost certainly be "$finished_child == $_".

> The code:

[snipped]

Anno

--
$anagram = 'Knuth heals rare project'; # by Abigail
push @{ $pos{ $_}}, $pos ++ for split //, lc $anagram;
print "print +(split //, '$anagram')[ $_]\n" for
join ', ', map shift @$_, @pos{ split //, lc "Just another Perl hacker"};

In our last episode, the evil Dr. Lacto had captured our hero,
"trxrse" <>, who said:
>I have a piece of code and I really don't understand what's
>happening...

Found it.

>print "Parent continues now...\n";
># Parent - wait for returned data
>while (&sum_pids > 0) {
> print "sum_pids=",&sum_pids,"\n";
> while (! $gotone){
> sleep 1;
> print "Slept 1\n";
> }
> $gotone=0;
> print "finished_child=$finished_child","\n";
> foreach (@kids){
vvvvv
> if ($finished_child=$_){
^^^^^
> print "\$finished_child=",$finished_child,"\n";
> print "\$_=",$_,"\n";
> print "I am the parent and process $_ finished!!!\n";
> $_=0;
> }
> }
>}

As soon as you finish your first child, you declare them all finished.
Thus the while loop only runs once.

hymie! http://www.smart.net/~hymowitz
================================================== =============================
When speaking to a Bear of Very Little Brain, remember that long words may
Bother him. -- Winnie the Pooh
================================================== =============================

Thanks very much both, that was the problem!!!


trxrse


hymie! wrote:
> In our last episode, the evil Dr. Lacto had captured our hero,
> "trxrse" <>, who said:
> >I have a piece of code and I really don't understand what's
> >happening...
>
> Found it.
>
> >print "Parent continues now...\n";
> ># Parent - wait for returned data
> >while (&sum_pids > 0) {
> > print "sum_pids=",&sum_pids,"\n";
> > while (! $gotone){
> > sleep 1;
> > print "Slept 1\n";
> > }
> > $gotone=0;
> > print "finished_child=$finished_child","\n";
> > foreach (@kids){
> vvvvv
> > if ($finished_child=$_){
> ^^^^^
> > print "\$finished_child=",$finished_child,"\n";
> > print "\$_=",$_,"\n";
> > print "I am the parent and process $_ finished!!!\n";
> > $_=0;
> > }
> > }
> >}
>
> As soon as you finish your first child, you declare them all finished.
> Thus the while loop only runs once.
>
> hymie! http://www.smart.net/~hymowitz
> ================================================== =============================
> When speaking to a Bear of Very Little Brain, remember that long words may
> Bother him. -- Winnie the Pooh
> ================================================== =============================