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 $end->(); redo; }
}
});
__END__
Benchmark: running for (;;), while (1), {; redo;},
each for at least 5 CPU seconds...
for (;;): 9 wsecs (5.48 usr + 0.01 sys = 5.49 CPU) @ 57.56/s (n=316)
while (1): 8 wsecs (5.26 usr + 0.01 sys = 5.27 CPU) @ 60.34/s (n=318)
{; redo;}: 8 wsecs (5.08 usr + 0.00 sys = 5.08 CPU) @ 57.68/s (n=293)
Rate for (;;) {; redo;} while (1)
for (;;) 57.6/s -- -0% -5%
{; redo;} 57.7/s 0% -- -4%
while (1) 60.3/s 5% 5% --
I've tried this many times.
while seems to be the winner.
Update (200201041112+0100)
This is really odd. I've run the benchmark above about a hundred times now, and
while won almost every one of them.
BUT
2;1 juerd@ouranos:~$ 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
Can anyone explain this?
2;0 juerd@ouranos:~$ perl -e'undef christmas'
Segmentation fault
2;139 juerd@ouranos:~$
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