Fork in Perl not working inside a while loop reading from file
- by Sag
Hi,
I'm running a while loop reading each line in a file, and then fork processes with the data of the line to a child. After N lines I want to wait for the child processes to end and continue with the next N lines, etc.
It looks something like this:
while ($w=<INP>) {
# ignore file header
if ($w=~m/^\D/) { next;}
# get data from line
chomp $w;
@ws = split(/\s/,$w);
$m = int($ws[0]);
$d = int($ws[1]);
$h = int($ws[2]);
# only for some days in the year
if (($m==3)and($d==15) or ($m==4)and($d==21) or ($m==7)and($d==18)) {
die "could not fork" unless defined (my $pid = fork);
unless ($pid) {
some instructions here using $m, $d, $h ...
}
push @qpid,$pid;
# when all processors are busy, wait for child processes
if ($#qpid==($procs-1)) {
for my $pid (@qpid) {
waitpid $pid, 0;
}
reset 'q';
}
}
}
close INP;
This is not working. After the first round of processes I get some PID equal to 0, the @qpid array gets mixed up, and the file starts to get read at (apparently) random places, jumping back and forth. The end result is that most lines in the file get read two or three times. Any ideas?
Thanks a lot in advance,
S.
