[ruby-core:28547] [Feature #905] Add String.new(fixnum) to preallocate large buffer

Issue #905 has been updated by Motohiro KOSAKI.


>$ cat test.rb
>require 'benchmark'
>opt = ARGV[0]
>list = Array.new(10) do
>  Benchmark.realtime do
>    1000.times do
>      s = ""
>      s.buffer(opt ? 100_001 : 100)
>      x = "x" * 1000
>      100.times { s << x }
>    end
>  end
>end
>list.sort!
>p list.first, list.last
>
>$ ./ruby -v -Ilib test.rb opt
>ruby 1.9.2dev (2010-03-07 trunk 26843) [i386-mingw32]
>0.1780099868774414
>0.18601107597351074
>
>$ ./ruby -v -Ilib test.rb
>ruby 1.9.2dev (2010-03-07 trunk 26843) [i386-mingw32]
>0.21401190757751465
>0.22301316261291504

Ah, yes. "x" * 1000 is not so big string. then, its realloc() doesn't use mremap.
It mean string concat(i.e. "<<" operator) cause string copy on each time. but is
this real issue? Does small string copy makes big peformance issue? when? So, I
think we need good realistic benchmark.

Thanks.
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