Some say for(;;) is inefficient, because it's a C-style loop.
Some say {; redo;} is inefficient, because it won't let perl optimize.
Some say while(1) is inefficient, because the 1 has to be evaluated over and oer.

I wanted to know, so I benchmarked. I found it somewhat hard to benchmark infinite loops, so I made them finite with a nice closure construct.

#!/usr/bin/perl -w
use strict;
use Benchmark;

sub ender () {
    my $i = 0;
    return sub { ++$i == 10000 }
}

Benchmark::cmpthese(-5, {
    'for (;;)'  => sub {
        my $end = ender();
        for (;;) { last if $end->() }
    },
    'while (1)' => sub {
        my $end = ender();
        while (1) { last if $end->() }
    },
    '{; redo;}' => sub {
        my $end = ender();
        { last if $end->(); redo; }
    }
});
__END__
Benchmark: running for (;;), while (1), {; redo;},
each for at least 5 CPU seconds...
 for (;;): 9 wsecs (5.48 usr + 0.01 sys = 5.49 CPU) @ 57.56/s (n=316)
while (1): 8 wsecs (5.26 usr + 0.01 sys = 5.27 CPU) @ 60.34/s (n=318)
{; redo;}: 8 wsecs (5.08 usr + 0.00 sys = 5.08 CPU) @ 57.68/s (n=293)
            Rate  for (;;) {; redo;} while (1)
for (;;)  57.6/s        --       -0%       -5%
{; redo;} 57.7/s        0%        --       -4%
while (1) 60.3/s        5%        5%        --

[download]


I've tried this many times. while seems to be the winner.

Update (200201041112+0100)
This is really odd. I've run the benchmark above about a hundred times now, and while won almost every one of them.

BUT 
2;1 juerd@ouranos:~$ perl -MO=Deparse -e'while (1) { print "1\n" }'
for (;;) {
    print "1\n";
}
-e syntax OK
2;0 juerd@ouranos:~$ perl -MO=Deparse -e'for (;;) { print "1\n" }'
for (;;) {
    print "1\n";
}
-e syntax OK

[download]

Can anyone explain this? 

2;0 juerd@ouranos:~$ perl -e'undef christmas'
Segmentation fault
2;139 juerd@ouranos:~$

[download]

In reply to Re: do/redo or for(;;): what's Kosher? by Juerd
in thread do/redo or for(;;): what's Kosher? by rje

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