stdio performance in tango, stdlib, and perl

[Andrei Alexandrescu (See Website For Email)]

James Dennett wrote:
> Andrei Alexandrescu (See Website For Email) wrote:
>> Walter Bright wrote:
>>> Andrei Alexandrescu (See Website For Email) wrote:
>>>> I've ran a couple of simple tests comparing Perl, D's stdlib (the
>>>> coming release), and Tango.
>>> Can you add a C++ <iostream> to the mix? I think that would be a very
>>> useful additional data point.
>> Obliged. Darn, I had to wait a *lot* longer.
>>
>> #include <string>
>> #include <iostream>
>>
>> int main() {
>>   std::string s;
>>   while (getline(std::cin, s)) {
>>     std::cout << s << '\n';
>>   }
>> }
>>
>> (C++ makes the same mistake wrt newline.)
>>
>> 35.7s        cppcat
>>
>> I seem to remember a trick that puts some more wind into iostream's
>> sails, so I tried that as well:
>>
>> #include <string>
>> #include <iostream>
>> using namespace std;
>>
>> int main() {
>>   cin.sync_with_stdio(false);
>>   cout.sync_with_stdio(false);
>>   string s;
>>   while (getline(std::cin, s)) {
>>     cout << s << '\n';
>>   }
>> }
>>
>> Result:
>>
>> 13.3s        cppcat
> 
> Try the way IOStreams would be used if you didn't want
> it to go slowly:
> 
> #include <string>
> #include <iostream>
> 
> int main() {
>     std::ios_base::sync_with_stdio(false);
>     std::cin.tie(NULL);
>     std::string s;
>     while (std::getline(std::cin, s)) {
>         std::cout << s << '\n';
>     }
> }
> 
> (Excuse the lack of a using directive there; I find the
> code more readable without them.  YMMV.)

With your code pasted and wind from behind:

13.5s		cppcat

> I don't have your sample file or your machine, but for
> the quick tests I just ran on this one machine, the code
> above runs move than 60% faster.  Without using tie(),
> each read from standard input causes a flush of standard
> output (so that, by default, they work appropriately for
> console I/O).
> 
> It's certainly true that making efficient use of IOStreams
> needs some specific knowledge, and that writing an
> efficient implementation of IOStreams is far from trivial.
> But if we're comparing to C++, we should probably compare
> to some reasonably efficient idiomatic C++.

The sync_with_stdio and tie tricks are already unknown to most 
programmers, so it would be an uphill battle to characterize them as 
idiomatic. They are idiomatic for a small group at best.

But, obviously not enough. Perl does way better.

(Again: gcc on Linux.)


Andrei