5 messages in org.apache.incubator.stdcxx-devRe: stdcxx stringstreams 2x slower th...| From | Sent On | Attachments |
|---|---|---|
| Mark Brown | May 6, 2008 3:57 pm | |
| Martin Sebor | May 6, 2008 8:42 pm | |
| Eric Lemings | May 7, 2008 7:30 am | |
| Martin Sebor | May 7, 2008 7:38 am | |
| Eric Lemings | May 7, 2008 8:01 am |
| Subject: | Re: stdcxx stringstreams 2x slower than gcc | |
|---|---|---|
| From: | Martin Sebor (seb...@roguewave.com) | |
| Date: | May 6, 2008 8:42:32 pm | |
| List: | org.apache.incubator.stdcxx-dev | |
Mark Brown wrote:
Hi again!
Hey Mark!
While testing my own implementation of lexical cast I discovered that the stdcxx stringstreams are nearly twice as slow as gcc's. I created a small test program to convince myself of the difference. On my x86_64 Linux PC it takes 16 seconds to run through 10 million loops when using stdcxx but just 9 seconds with gcc. Is there some option or trick that I don't know about to speed things up? Or maybe a quick fix that I could work on?
Funny! I get the opposite result with gcc 4.3 in an 8D (shared, optimized, NOT reentrant) build. Your program runs in 9 seconds with stdcxx and over 15 seconds with g++. In 12D though, and with gcc 4.1.2, the results are reversed. In 12D with gcc 4.2, both programs take 15 seconds.
I think the difference between 8D and 12D is due to the mutex in stingstream. Even though there's no locking the mutex still is initialized and that's what I suspect accounts for the slow runtimes. We need an issue to remind us to fix it as soon as binary compatibility permits it. As for gcc, I can only guess that libstdc++ has regressed between 4.1.2 and 4.3.
Martin
Cheers -- Mark
#include <stdio.h> #include <stdlib.h> #include <string> #include <sstream> #include <typeinfo>
template <class To, class From> To lex_cast(const From &source) { std::stringstream converter;
To dest;
if ((converter << source) && (converter >> dest)) return dest;
throw std::bad_cast(); }
int main(int argc, char *argv[]) { long loops = atol(argv [1]);
long long sum = 0;
std::string str;
for (long i = 0; i < loops; ++i) { str = lex_cast<std::string>(i); sum += str.length(); }
printf("%llu\n", sum); }