[STDCXX-518] std::string copy constructor slow

• Type: Improvement
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 4.1.3
• Fix Version/s: 4.2.1
• Component/s: 21. Strings

Environment

gcc 4.1.2, x86_64

• Severity: Inefficiency
• Assignee: Travis Vitek
• Reporter: Mark Brown
• Created: 11/Aug/07 23:48
• Updated: 09/Jan/08 16:56
• Resolved: 08/Jan/08 21:56

Description

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); }

}

Issue Links

• duplicates: STDCXX-162 [x86_64] atomic operations disabled