in reply to Re^4: while reading a file, transfer the same data to two different processes.
in thread while reading a file, transfer the same data to two different processes.

Thanks. If you've the inclination to indulge me a little further, what results do you get from the following? 

use strict;
use warnings;
use threads;

my $str = 'x' x 32_000_000;

sub fork_wait {
    my $pid = fork;
    if ($pid) {
        wait;
    }
    else {
        my $l = length( $str );
        exit 0;
    }
}

sub create_thread_join {
    threads->create( sub { my $l = length( $str ) } )->join;
}

use Benchmark qw( cmpthese );

cmpthese - 3,
  {
    Forks   => \&fork_wait,
    Threads => \&create_thread_join,
  };

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Re^6: while reading a file, transfer the same data to two different processes.
by almut (Canon) on May 20, 2010 at 23:57 UTC 
              Rate Threads   Forks
Threads 25.2/s      --    -54%
Forks   54.7/s    118%      --

perl v5.10.1 built for x86_64-linux-thread-multi  (Ubuntu 8.04)


          Rate Threads   Forks
Threads 21.5/s      --    -72%
Forks   77.6/s    261%      --

perl v5.12.0 built for x86_64-linux-thread-multi  (openSUSE 11.1)

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      Interesting, thank you Almut.

      If you have time & inclination, I've one final line of enquiry: 

      use strict;
use warnings;
use threads;

my $str = 'x' x 32_000_000;

sub fork_wait {
    my $pid = fork;
    if ($pid) {
        wait;
    }
    else {
        substr( $str, $_, 1 ) &= ~ ' ' for 0 .. length( $str ) -1;
        exit 0;
    }
}

sub create_thread_join {
    threads->create( sub {
        substr( $str, $_, 1 ) &= ~ ' ' for 0 .. length( $str ) -1;
    } )->join;
}

use Benchmark qw( cmpthese );

cmpthese - 3,
  {
    Forks   => \&fork_wait,
    Threads => \&create_thread_join,
  };

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        As given, the benchmark didn't complete within more than half an hour (not sure why this is so excruciatingly slow). So I stopped it, and reduced the string length 

        my $str = 'x' x 1_000_000;
...
cmpthese 100,
...

        [download]

        Results (similar on both above machines/versions of Perl): 

                  Rate Threads   Forks
Threads 2.02/s      --     -4%
Forks   2.11/s      5%      --

        [download]

        (which is not all that surprising, I guess, as modifying the string results in copy-on-write, which destroys fork's advantage)

        Also, the time taken to fiddle with the string here far outweighs the time needed to create a new thread or process...

        Update: with a significantly shorter string, threads actually become faster, with an optimum advantage at a length of around 100 to 10000 (for this particular code sample): 

                  Rate   Forks Threads
Forks   67.1/s      --    -64%
Threads  189/s    181%      --

(v5.10.1, Ubuntu 8.04 (kernel 2.6.24), string length 100)


          Rate   Forks Threads
Forks   84.7/s      --    -44%
Threads  152/s     79%      --

(v5.12.0, SUSE 11.1 (kernel 2.6.27), string length 10000)

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