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https://issues.apache.org/jira/browse/STDCXX-518?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12557049#action_12557049
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Travis Vitek commented on STDCXX-518:
-------------------------------------
This is a known issue. At one time in the past we didn't have atomic operation
support for amd64 and emt64 platforms running Linux. As a result we used a
per-string mutex to protect per-string data. Since that time we added the
necessary atomic operation support. Unfortunately, due to binary compatibility
requirements, we cannot switch the implementation until the next major version.
Please see http://svn.apache.org/viewvc?view=rev&revision=585998.
> 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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