From: Brian Takita <brian.takita@...>
Date: 2006-10-01T14:21:31+09:00
Subject: Re: What is the fastest way to iterate over a hash in C?

------=_Part_5222_20972024.1159680087560
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
Content-Transfer-Encoding: 7bit
Content-Disposition: inline

I found a better solution in c. This method causes the benchmark to run in
about 1.4 seconds.

static VALUE process_internal_json(VALUE self, VALUE json, VALUE state,
VALUE depth, VALUE delim) {
  VALUE key_value_pairs = rb_funcall(self, rb_intern("to_a"), 0);

  VALUE key_value = Qnil;
  int i;
  for( i = 0; i < RARRAY(key_value_pairs)->len; i++) {
    if(i > 0) {
      rb_str_concat(json, delim);
    }
    VALUE key_value = rb_ary_entry(key_value_pairs, i);
    VALUE key = rb_ary_entry(key_value, 0);
    VALUE value = rb_ary_entry(key_value, 1);
    generate_key_value_json(self, json, state, depth, key, value);
  }
}



On 9/30/06, Brian Takita <brian.takita@gmail.com> wrote:
>
> Hello,
>
> I'm working on the Fast JSON project, and have come against some puzzling
> performance quirk.
>
> Most of the Hash#to_json functionality is implemented in C and performs
> much
> better. However there is one section that performs 6 time better when
> implemented in ruby vs c.
>
> I wrote a benchmark that calls to_json on 50000 hashes.
>
> Here is the method in Ruby. The benchmark takes around 1.7 seconds:
>
>   def process_internal_json(json, state, depth, delim)
>     first = true
>     each { |key,value|
>       if first
>         first = false
>       else
>         json << delim
>       end
>       generate_key_value_json(json, state, depth, key, value)
>     }
>     json
>   end
>
> Here is the method in C. The benchmark takes around 9.5 seconds:
>
> static VALUE process_internal_json(VALUE self, VALUE json, VALUE state,
> VALUE depth, VALUE delim) {
>   int first = 1;
>   VALUE key_value_pairs = rb_funcall(self, rb_intern("to_a"), 0);
>
>   VALUE key_value = Qnil;
>   while((key_value = rb_ary_pop(key_value_pairs)) != Qnil) {
>     if(first == 1) {
>       first = 0;
>     }
>     else {
>       rb_str_concat(json, delim);
>     }
>     VALUE value = rb_ary_pop(key_value);
>     VALUE key = rb_ary_pop(key_value);
>     generate_key_value_json(self, json, state, depth, key, value);
>   }
> }
>
> It seems like there is some optimization in the Hash#each method. I'm
> trying
> to figure out how to get that same performance benefit using C. Perhaps
> its
> is not worth it though.
>
> Does anybody know what going on?
>
> Thank you,
> Brian Takita
>
>

------=_Part_5222_20972024.1159680087560--