While vs loop

ruby-talk
1

Hi,I saw this thread from last week: while vs loop,

I don't think anybody mentioned the slight performance difference between
the two,
(or maybe I got the wrong info!!)
In fact, I had always assumed the 'loop do' construct to be better than
'while 1 do', if only to be more elegant or concise for implementing
infinite loops... but it turns out it seems to be the other way:

···

##############
require 'benchmark'
Benchmark.bm do |x|
x.report('while1') do
n = 0
while 1 do
break if n >= 10000000
n += 1
end
end
x.report('loop ') do
n = 0
loop do
break if n >= 10000000
n += 1
end
end
end

##############
RESULTS:

                   user system total real
while 1 19.770000 0.230000 20.000000 ( 34.458926)
loop 25.870000 0.300000 26.170000 ( 42.804569)

###########

I'm running this benchmark on 1.8.6 patchlevel 114 (universal-darwin9.0)

So why is it behaving this way?
Are every implementations doing the same?

Thanks!

L-P

On Sat, Feb 14, 2009 at 7:16 AM, Nobuyoshi Nakada <n...<http://groups.google.com/groups/unlock?_done=/group/ruby-talk-google/browse_thread/thread/3ee74ef131ec90ba&msg=2f988b0deb69e61d&gt; @ruby-lang.org> wrote:

Hi,

At Sat, 14 Feb 2009 15:03:03 +0900,
Vetrivel Vetrivel wrote in [ruby-talk:328175]:

what is the Difference between loop and while in ruby ?

loop do
end

loop is a kernel method which takes a block. A block
introduces new local variable scope.

loop do
   a = 1
   break
end
p a #=> causes NameError

while 1
end

while doesn't.

while 1
   a = 1
   break
end
p a #=> 1

--
Nobu Nakada

furthermore loop do has an implicit rescue clause for a StopIteration
exception
(I believe 1.8.7 and 1.9.1 only IIRC)

therefore

loop do
   some_enumerator.next
end
becomes a convenient idiom.

HTH
Robert

2

Hi,I saw this thread from last week: while vs loop,

I don't think anybody mentioned the slight performance difference between
the two,

If you're going to talk performance differences between while and loop, don't forget for and each:

% ./x.rb 1000000
# of iterations = 1000000
                          user system total real
each 0.150000 0.000000 0.150000 ( 0.148313)
for 0.170000 0.000000 0.170000 ( 0.173150)
each-var 0.230000 0.000000 0.230000 ( 0.237410)
while 0.640000 0.010000 0.650000 ( 0.644029)
loop 0.780000 0.000000 0.780000 ( 0.785485)
% ./x.rb 10000000
# of iterations = 10000000
                          user system total real
each 1.370000 0.010000 1.380000 ( 1.380012)
for 1.630000 0.000000 1.630000 ( 1.652562)
each-var 2.450000 0.010000 2.460000 ( 2.479478)
while 5.510000 0.010000 5.520000 ( 5.532909)
loop 7.730000 0.020000 7.750000 ( 7.786959)

require 'benchmark'

max = (ARGV.shift || 1_000_000).to_i

puts "# of iterations = #{max}"
Benchmark::bm(20) do |x|
   x.report("each") do
     (0..max).each do
     end
   end

   x.report("for") do
     for i in 0..max do
       # do nothing
     end
   end

   x.report("each-var") do
     (0..max).each do |i|
     end
   end

   x.report("while") do
     n = 0
     while true do
       break if n >= max
       n += 1
     end
   end

   x.report("loop") do
     n = 0
     loop do
       break if n >= max
       n += 1
     end
   end
end

···

On Feb 20, 2009, at 13:57 , Louis-Philippe wrote:

3

mmm, Interesting to see loop being this high in the list,
but even if they all loop from 0 to X doesn't mean they can all compared...
I'm not sure what was the initial question (!!!), but mine is about infinite
loop implementations,
where list iterators of the .each flavour don't do.

So *THE* fastest ruby infinite loop is 'while 1'?

···

2009/2/20 Ryan Davis <ryand-ruby@zenspider.com>

On Feb 20, 2009, at 13:57 , Louis-Philippe wrote:

Hi,I saw this thread from last week: while vs loop,

I don't think anybody mentioned the slight performance difference between
the two,

If you're going to talk performance differences between while and loop,
don't forget for and each:

% ./x.rb 1000000

# of iterations = 1000000
                         user system total real
each 0.150000 0.000000 0.150000 ( 0.148313)
for 0.170000 0.000000 0.170000 ( 0.173150)
each-var 0.230000 0.000000 0.230000 ( 0.237410)
while 0.640000 0.010000 0.650000 ( 0.644029)
loop 0.780000 0.000000 0.780000 ( 0.785485)
% ./x.rb 10000000
# of iterations = 10000000
                         user system total real
each 1.370000 0.010000 1.380000 ( 1.380012)
for 1.630000 0.000000 1.630000 ( 1.652562)
each-var 2.450000 0.010000 2.460000 ( 2.479478)
while 5.510000 0.010000 5.520000 ( 5.532909)
loop 7.730000 0.020000 7.750000 ( 7.786959)

require 'benchmark'

max = (ARGV.shift || 1_000_000).to_i

puts "# of iterations = #{max}"
Benchmark::bm(20) do |x|
x.report("each") do
   (0..max).each do
   end
end

x.report("for") do
   for i in 0..max do
     # do nothing
   end
end

x.report("each-var") do
   (0..max).each do |i|
   end
end

x.report("while") do
   n = 0
   while true do
     break if n >= max
     n += 1
   end
end

x.report("loop") do
   n = 0
   loop do
     break if n >= max

     n += 1
   end
end
end

4

mmm, Interesting to see loop being this high in the list,
but even if they all loop from 0 to X doesn't mean they can all compared...
I'm not sure what was the initial question (!!!), but mine is about infinite
loop implementations,
where list iterators of the .each flavour don't do.

So *THE* fastest ruby infinite loop is 'while 1'?

wrong

···

On Feb 20, 2009, at 15:02 , Louis-Philippe wrote:

>> Infinity = 1 / 0.0
=> Infinity
>> (0..Infinity).each {}

5

Anything purporting to be an infinite loop which runs faster than something
which is an infinite loop is, by definition NOT an infinite loop!
<G>

···

On Fri, Feb 20, 2009 at 6:02 PM, Louis-Philippe <default@spiralix.org>wrote:

mmm, Interesting to see loop being this high in the list,
but even if they all loop from 0 to X doesn't mean they can all
compared...
I'm not sure what was the initial question (!!!), but mine is about
infinite
loop implementations,
where list iterators of the .each flavour don't do.

So *THE* fastest ruby infinite loop is 'while 1'?

--
Rick DeNatale

Blog: http://talklikeaduck.denhaven2.com/
Twitter: http://twitter.com/RickDeNatale
WWR: http://www.workingwithrails.com/person/9021-rick-denatale
LinkedIn: http://www.linkedin.com/in/rickdenatale

6

Rick DeNatale wrote:

Anything purporting to be an infinite loop which runs faster than something
which is an infinite loop is, by definition NOT an infinite loop!
<G>

Not sure Georg Cantor would agree with you. One infinite loop might only go through a countable (but infinite) number of iterations, i.e. aleph null, whereas another might go through an uncountable number of iterations.

Suppose one loop iterates over just the rationals, while another iterates over the reals. The former iterates fewer times than the latter, even though both are infinite.

Still, your point is well taken. :slight_smile:

7

This was one of the most famous stories in our department . We were
developing a Debugger and my colleague was debugging an infinite loop,
which happened to be inside another infinite loop. Of course he did
not discover the problem of the outer infinite loop before having
fixed the inner one.
When our project leader asked him about the progress he had made, he
genuinely replied: "It still loops, but much faster". We happened to
pull his leg for quite some time of course :)?
Robert

···

On Sat, Feb 21, 2009 at 3:42 PM, Rick DeNatale <rick.denatale@gmail.com> wrote:

On Fri, Feb 20, 2009 at 6:02 PM, Louis-Philippe <default@spiralix.org>wrote:

Anything purporting to be an infinite loop which runs faster than something
which is an infinite loop is, by definition NOT an infinite loop!
<G>

--
There are some people who begin the Zoo at the beginning, called
WAYIN, and walk as quickly as they can past every cage until they get
to the one called WAYOUT, but the nicest people go straight to the
animal they love the most, and stay there. ~ A.A. Milne (from
Winnie-the-Pooh)

8

Might it? I do not think so! I believe that a Turing complete language
can only loop countable times, which of course should be fixed ;).
R.

···

On Sat, Feb 21, 2009 at 4:49 PM, Jeff Schwab <jeff@schwabcenter.com> wrote:

Rick DeNatale wrote:

Anything purporting to be an infinite loop which runs faster than
something
which is an infinite loop is, by definition NOT an infinite loop!
<G>

Not sure Georg Cantor would agree with you. One infinite loop might only go
through a countable (but infinite) number of iterations, i.e. aleph null,
whereas another might go through an uncountable number of iterations.

--
There are some people who begin the Zoo at the beginning, called
WAYIN, and walk as quickly as they can past every cage until they get
to the one called WAYOUT, but the nicest people go straight to the
animal they love the most, and stay there. ~ A.A. Milne (from
Winnie-the-Pooh)

9

This is indeed very fun and mind boggling!Still, pragmatically, not all
infinite loops are equal, in the performance of their implementations that
is.
So taking Ryan's idea to twist iterators to perform infinite loops, here is
the benchmark again.

For the comparison to be as close as possible between the control
structures, I use the same inner routine for all, ignoring the fact that I
could derive incrementation from the infinite range iteration, because this
is not the subject of the benchmark.

Ruby Infinite loops Inplementations:
                           user system total real
while1 31.960000 0.150000 32.110000 ( 36.749597)
loop 42.240000 0.190000 42.430000 ( 45.533708)
Infinite.each 108.400000 0.970000 109.370000 (117.421059)
for Infinite 112.070000 1.010000 113.080000 (126.712828)

···

#############

Benchmark.bm do |x|
x.report('while1') do
n = 0
while 1 do
break if n >= 1000000
n += 1
end
end
x.report('loop') do
n = 0
loop do
break if n >= 1000000
n += 1
end
end
x.report('Infinite.each') do
n = 0
(0..(1/0.0)).each do
break if n >= 1000000
n += 1
end
end
x.report('for Infinite') do
n = 0
for i in (0..(1/0.0)) do
break if n >= 1000000
n += 1
end
end
end

#############

2009/2/21 Robert Dober <robert.dober@gmail.com>

On Sat, Feb 21, 2009 at 4:49 PM, Jeff Schwab <jeff@schwabcenter.com> > wrote:
> Rick DeNatale wrote:
>
>> Anything purporting to be an infinite loop which runs faster than
>> something
>> which is an infinite loop is, by definition NOT an infinite loop!
>> <G>
>
> Not sure Georg Cantor would agree with you. One infinite loop might only
go
> through a countable (but infinite) number of iterations, i.e. aleph null,
> whereas another might go through an uncountable number of iterations.
Might it? I do not think so! I believe that a Turing complete language
can only loop countable times, which of course should be fixed ;).
R.

--
There are some people who begin the Zoo at the beginning, called
WAYIN, and walk as quickly as they can past every cage until they get
to the one called WAYOUT, but the nicest people go straight to the
animal they love the most, and stay there. ~ A.A. Milne (from
Winnie-the-Pooh)