[jira] Closed: (STDCXX-518) std::string copy constructor slow

[Travis Vitek (JIRA)]

     [ 
https://issues.apache.org/jira/browse/STDCXX-518?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
 ]

Travis Vitek closed STDCXX-518.
-------------------------------

    Resolution: Fixed

I did a quick test to verify. I built the library and test with 'gmake 
CXXOPTS=_RWSTD_USE_STRING_ATOMIC_OPS', and then ran it. Here is the 
comparison...

$ time ./string-copy.stdcxx 100000000

real    0m4.279s
user    0m4.271s
sys     0m0.003s
$ time ./string-copy.gcc 100000000

real    0m4.392s
user    0m4.378s
sys     0m0.008s


> std::string copy constructor slow
> ---------------------------------
>
>                 Key: STDCXX-518
>                 URL: https://issues.apache.org/jira/browse/STDCXX-518
>             Project: C++ Standard Library
>          Issue Type: Improvement
>          Components: 21. Strings
>    Affects Versions: 4.1.3
>         Environment: gcc 4.1.2, x86_64
>            Reporter: Mark Brown
>            Assignee: Travis Vitek
>             Fix For: 4.2.1
>
>
> When thread safety is enabled in stdcxx the string copy constructor is more 
> than ten times slower than when it's not, and twice as slow as the same copy 
> constructor in gcc 4.1.2 on Linux (x86_64), but slightly faster than with 
> STLport 5.1.3. The timings were done on Intel x86_64 at 2.4GHz:
> BUILDMODE=shared,optimized:
> $ time LD_LIBRARY_PATH=../lib ./string-copy 100000000
> real    0m0.482s
> user    0m0.480s
> sys     0m0.000s
> BUILDMODE=shared,optimized,pthread:
> $ time LD_LIBRARY_PATH=../lib ./string-copy 100000000
> real    0m10.157s
> user    0m10.041s
> sys     0m0.032s
> gcc 4.1.2 with -O2 -m64:
> $ time ./string-copy.gcc 100000000
> real    0m4.280s
> user    0m4.260s
> sys     0m0.020s
> gcc 4.1.2 with STLport 5.1.3 (-D_REENTRANT -O2 -m64 -lpthread):
> $ time ./string-copy.stlport 100000000
> real    0m12.479s
> user    0m12.473s
> sys     0m0.004s
> #include <cassert>
> #include <cstdlib>
> #include <string>
> int main (int argc, char *argv[])
> {
>     const unsigned long n = argc < 2 ? 0 : std::strtoul (argv [1], 0, 10);
>     std::string strings [256];
>     const std::size_t num_strings = sizeof strings / sizeof *strings;
>     for (unsigned long i = 0; i != num_strings; ++i)
>         strings [i].assign (i, 'x');
>     for (unsigned long i = 0; i < n; ++i) {
>         const std::size_t length = i % num_strings;
>         const std::string str (strings [length]);
>         assert (str.size () == length);
>     }
> }

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