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

Hi, Monks

I have very strange problem today. I run some code which works in the past but now it did't fork as i expect.

#!/usr/bin/perl use strict; use warnings; my %pids; my @chunk_indixes = find_chunk_indixes( 100, 10 ); foreach my $thread_id ( 0 .. 9 ) { if ( my $pid = fork() ) { $pids{$pid}++; } else { my $start = $chunk_indixes[$thread_id]->[0]; my $end = $chunk_indixes[$thread_id]->[1]; print "[$start, $end]\n"; sleep(10); exit; } while (%pids) { my $pid = waitpid( -1, 0 ); delete $pids{$pid}; } } sub find_chunk_indixes { my ( $total_size, $number_of_chunks ) = @_; my @result; my $small_chunk = int( $total_size / $number_of_chunks ); my $oversized_count = $total_size % $number_of_chunks; my @chunk_sizes = ( ( 1 + $small_chunk ) x ($oversized_count), ($ +small_chunk) x ( $number_of_chunks - $oversized_count ) ); my $current_position = 0; foreach my $chunk_size (@chunk_sizes) { push @result, [ $current_position, $current_position + $chunk_ +size - 1 ]; $current_position += $chunk_size; } return @result; }

I expect it forks 10 process at same time and prints

0, 9
10, 19
20, 29
30, 39
40, 49
50, 59
60, 69
70, 79
80, 89
90, 99
at same moment but it prints only one range, wait for ten second and prints another range and so one.

Process explorer shows me only two process of this script. Also i test this on Windows XP in Linux -- same result.

Can you show me what's wrong with this program?

Thanks.
Roman

Replies are listed 'Best First'.
Re: fork() not working as expected
by Crackers2 (Parson) on Mar 21, 2009 at 05:31 UTC

    The while (%pids) block should be outside of the foreach.

    Right now you're doing a fork and then waiting for the child to finish before starting the next one.

Re: fork() not working as expected
by zentara (Cardinal) on Mar 21, 2009 at 11:07 UTC
    From the variables chosen in your code, it seems you have fork and threads somewhat confused..... at least enough that I won't strain my brain trying to decipher your intent. Of course, if you are on MSWindows, ignore this. :-)

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