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From "Martin Sebor (JIRA)" <j...@apache.org>
Subject [jira] Issue Comment Edited: (STDCXX-914) sstream ctors inefficient in reentrant modes
Date Sat, 08 Nov 2008 19:04:44 GMT

    [ https://issues.apache.org/jira/browse/STDCXX-914?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12646021#action_12646021
] 

sebor edited comment on STDCXX-914 at 11/8/08 11:02 AM:
---------------------------------------------------------------

Here's a superficially tested patch to optimize {{__rw_locale::_C_is_managed()}} in {{[src/locale_body.cpp|http://svn.eu.apache.org/viewvc/stdcxx/trunk/src/locale_body.cpp?revision=651334&view=markup]}}.
It improves the performance of the test case by about 25% by avoiding expensive tests for
named faces in the "C" locale.
\\
\\
{noformat}
Index: src/locale_body.cpp
===================================================================
--- src/locale_body.cpp (revision 712407)
+++ src/locale_body.cpp (working copy)
@@ -1066,6 +1066,15 @@
             return false;
         }
 
+        _RWSTD_ASSERT (0 == _C_usr_facets);
+
+        if (_C_all == _C_std_facet_bits && 0 == _C_byname_facet_bits) {
+            // optimized for the C locale
+            _RWSTD_ASSERT (__rw_is_C (_C_name));
+
+            return true;
+        }
+
         // unless all facets in the same category come either from
         // the C locale or from some named locale the locale object
         // containing the facets is not managed (this test doesn't
{noformat}

With the patch applied, the top 10 list looks like so:
\\
\\
{noformat}
Each sample counts as 0.01 seconds.
  %   cumulative   self              self     total           
 time   seconds   seconds    calls  ms/call  ms/call  name    
 24.54      1.45     1.45 50000001     0.00     0.00  __rw::__rw_locale::_C_manage(__rw::__rw_locale*,
char const*)
  9.48      2.01     0.56 10000000     0.00     0.00  std::basic_istream<char, std::char_traits<char>
>& std::operator>><char, std::char_traits<char>, std::allocator<char>
>(std::basic_istream<char, std::char_traits<char> >&, std::basic_string<char,
std::char_traits<char>, std::allocator<char> >&)
  7.11      2.43     0.42 10000001     0.00     0.00  std::money_put<char, std::ostreambuf_iterator<char,
std::char_traits<char> > >::_C_put(std::ostreambuf_iterator<char, std::char_traits<char>
>, int, std::ios_base&, char, char const*, unsigned long, int, char const*, unsigned
long) const
  6.94      2.84     0.41 40000003     0.00     0.00  std::locale::_C_get_std_facet(__rw::__rw_facet::_C_facet_type,
__rw::__rw_facet* (*)(unsigned long, char const*)) const
  6.77      3.24     0.40 10000000     0.00     0.00  std::num_put<char, std::ostreambuf_iterator<char,
std::char_traits<char> > >::_C_put(std::ostreambuf_iterator<char, std::char_traits<char>
>, std::ios_base&, char, int, void const*) const
  5.58      3.57     0.33 10000001     0.00     0.00  __rw::__rw_itoa(char*, unsigned long
long, unsigned int)
  4.91      3.86     0.29 10000000     0.00     0.00  std::basic_ostream<char, std::char_traits<char>
>& __rw::__rw_insert<char, std::char_traits<char>, long>(std::basic_ostream<char,
std::char_traits<char> >&, long)
  4.57      4.13     0.27                             std::basic_iostream<char, std::char_traits<char>
>::~basic_iostream()
  3.13      4.32     0.19 10000000     0.00     0.00  std::string::replace(unsigned long,
unsigned long, char const*, unsigned long)
  2.88      4.49     0.17 10000000     0.00     0.00  std::string lex_cast<std::string,
long>(long const&)
{noformat}


      was (Author: sebor):
    Here's a superficially tested patch to optimize {{__rw_locale::_C_is_managed()}} in {{[src/locale_body.cpp|http://svn.eu.apache.org/viewvc/stdcxx/trunk/src/locale_body.cpp?revision=651334&view=markup]}}.
It improves the performance of the test case by about 25% by avoiding expensive tests for
named faces in the "C" locale.
\\
\\
{noformat}
Index: src/locale_body.cpp
===================================================================
--- src/locale_body.cpp (revision 712407)
+++ src/locale_body.cpp (working copy)
@@ -1066,6 +1066,15 @@
             return false;
         }
 
+        _RWSTD_ASSERT (0 == _C_usr_facets);
+
+        if (_C_all == _C_std_facet_bits && 0 == _C_byname_facet_bits) {
+            // optimized for the C locale
+            _RWSTD_ASSERT (__rw_is_C (_C_name));
+
+            return true;
+        }
+
         // unless all facets in the same category come either from
         // the C locale or from some named locale the locale object
         // containing the facets is not managed (this test doesn't
{noformat}
  
> sstream ctors inefficient in reentrant modes
> --------------------------------------------
>
>                 Key: STDCXX-914
>                 URL: https://issues.apache.org/jira/browse/STDCXX-914
>             Project: C++ Standard Library
>          Issue Type: Improvement
>          Components: 27. Input/Output
>    Affects Versions: 4.1.2, 4.1.3, 4.1.4, 4.2.0, 4.2.1
>            Reporter: Martin Sebor
>            Priority: Critical
>             Fix For: 4.2.2
>
>         Attachments: stdcxx-914-gprof-gcc-4.1.2-12D.txt, stdcxx-914-gprof-gcc-4.3.0-12S.txt
>
>   Original Estimate: 12h
>          Time Spent: 1h
>  Remaining Estimate: 11h
>
> As discussed in this [thread|http://markmail.org/message/hqlsw5dq23gx7d4o] stream ctors
in thread-safe builds are inefficient due to the initialization of the mutex data member in
every stream, even in those that never use it. As soon as binary compatibility rules permit
it we should remove the mutex and/or defer its initialization until it's needed. It might
be possible to implement the deferred initialization as early as 4.2.2, or maybe 4.3. Complete
removal will need to wait until 5.0.

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