I did some benchmarking of forking vs threading. Below is a program that compares the running times of programs that fork and that use threads. Two programs are compared: first a program where the children don't do much (exit for the fork, empty sub for the threads). In the second program, the children print a single character to /dev/null. 
#!/usr/bin/perl
  
use strict;
use warnings;

my $perl    = "/opt/perl/bin/perl";
my $thrperl = "/opt/perl/bin/thrperl";

my $action  = << '--';
    open my $fh => "> /dev/null" or die "open: $!";
    print $fh ".";
    close $fh;
--
    
my $prog    = << '--';
use strict;
use warnings;

my $times = shift;

my @pids;

foreach (1 .. $times) {
    defined (my $pid = fork) or die "fork: $!";
    unless ($pid) {
        ACTION;
        exit;
    }
    push @pids => $pid;
}
    
map {waitpid $_ => 0} @pids;

--


my $thrprog = << '--';
use strict;
use warnings;
use threads;
    
my $times = shift;
 
my @threads;

foreach (1 .. $times) {
    my $thread = threads -> create (sub {ACTION}) or die "threads: $!"
+;
    push @threads => $thread;
}

map {$_ -> join} @threads;

--
    
    
my @amounts = (0, 5, 10, 25, 50, 100, 250, 500, 1000, 2500);
  
print STDERR "Empty childs\n";

(my $t_prog    = $prog)    =~ s/ACTION//;
(my $t_thrprog = $thrprog) =~ s/ACTION//;
for my $amount (@amounts) {
    my $format = sprintf "%5d: %%U user, %%S system, %%E elapsed" => $
+amount;
    system time => '-f', "(F) $format",    $perl, '-e',    $t_prog, $a
+mount;
    system time => '-f', "(T) $format", $thrperl, '-e', $t_thrprog, $a
+mount;
}

    
print STDERR "\nChilds writing\n";
        
($t_prog    = $prog)    =~ s/ACTION/$action/;
($t_thrprog = $thrprog) =~ s/ACTION/$action/;
for my $amount (@amounts) {
    my $format = sprintf "%5d: %%U user, %%S system, %%E elapsed" => $
+amount;
    system time => '-f', "(F) $format",    $perl, '-e',    $t_prog, $a
+mount;
    system time => '-f', "(T) $format", $thrperl, '-e', $t_thrprog, $a
+mount;
}

__END__
Empty childs
(F)     0: 0.01 user, 0.00 system, 0:00.01 elapsed
(T)     0: 0.04 user, 0.00 system, 0:00.03 elapsed
(F)     5: 0.01 user, 0.00 system, 0:00.01 elapsed
(T)     5: 0.09 user, 0.00 system, 0:00.09 elapsed
(F)    10: 0.01 user, 0.01 system, 0:00.02 elapsed
(T)    10: 0.16 user, 0.00 system, 0:00.15 elapsed
(F)    25: 0.01 user, 0.02 system, 0:00.03 elapsed
(T)    25: 0.32 user, 0.02 system, 0:00.34 elapsed
(F)    50: 0.03 user, 0.04 system, 0:00.06 elapsed
(T)    50: 0.60 user, 0.08 system, 0:00.70 elapsed
(F)   100: 0.04 user, 0.08 system, 0:00.11 elapsed
(T)   100: 1.25 user, 0.11 system, 0:01.42 elapsed
(F)   250: 0.04 user, 0.12 system, 0:00.50 elapsed
(T)   250: 3.41 user, 0.24 system, 0:03.87 elapsed
(F)   500: 0.02 user, 0.14 system, 0:01.16 elapsed
(T)   500: 7.37 user, 0.55 system, 0:08.42 elapsed
(F)  1000: 0.05 user, 0.19 system, 0:02.49 elapsed
A thread exited while 46 threads were running.
(T)  1000: 15.02 user, 1.36 system, 0:17.42 elapsed
(F)  2500: 0.04 user, 0.71 system, 0:06.73 elapsed
Command terminated by signal 9
(T)  2500: 37.39 user, 3.30 system, 2:10.56 elapsed
    
Childs writing
(F)     0: 0.06 user, 0.21 system, 0:01.60 elapsed
(T)     0: 0.20 user, 0.23 system, 0:01.66 elapsed
(F)     5: 0.01 user, 0.01 system, 0:00.03 elapsed
(T)     5: 0.12 user, 0.02 system, 0:00.28 elapsed
(F)    10: 0.03 user, 0.00 system, 0:00.07 elapsed
(T)    10: 0.17 user, 0.04 system, 0:00.37 elapsed
(F)    25: 0.02 user, 0.06 system, 0:00.08 elapsed
(T)    25: 0.49 user, 0.09 system, 0:01.07 elapsed
(F)    50: 0.04 user, 0.21 system, 0:00.46 elapsed
(T)    50: 0.73 user, 0.12 system, 0:01.72 elapsed
(F)   100: 0.04 user, 0.11 system, 0:00.14 elapsed
(T)   100: 1.22 user, 0.06 system, 0:01.29 elapsed
(F)   250: 0.08 user, 0.12 system, 0:00.52 elapsed
(T)   250: 2.93 user, 0.30 system, 0:04.29 elapsed
(F)   500: 0.06 user, 0.20 system, 0:01.30 elapsed
(T)   500: 6.29 user, 0.67 system, 0:07.79 elapsed
(F)  1000: 0.03 user, 0.24 system, 0:02.50 elapsed
A thread exited while 46 threads were running.
(T)  1000: 11.52 user, 1.46 system, 0:13.84 elapsed
(F)  2500: 0.06 user, 0.72 system, 0:06.78 elapsed
Command terminated by signal 9
(T)  2500: 26.72 user, 13.98 system, 3:57.20 elapsed

[download]

As we can see, forking is much faster than creating threads. Furthermore, creating more than a thousand processes is not a problem - creating a thousand threads *is*. And what you didn't see was the slow response of my system when the threads were being handled, and neither did you hear the grinding of the disk when dealing with threads (2500 processes however was hardly noticeable).

Abigail

In reply to Re: Why use threads over processes, or why use processes over threads? by Abigail-II
in thread Why use threads over processes, or why use processes over threads? by pg

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