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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% --

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.

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

Can anyone explain this?

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

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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