From 749c0e1d8b2c8dbc54af3365af506b3e1986e754 Mon Sep 17 00:00:00 2001 From: Jonathan Wakely Date: Wed, 3 Oct 2018 12:27:40 +0100 Subject: [PATCH] PR libstdc++/59439 optimize uses of classic ("C") std::locale The global locale::_Impl that represents the "C" locale is never destroyed, so there is no need to keep track of reference count updates for that object. This greatly reduce contention between threads that refer to the classic locale. Since the global std::locale initially uses the classic locale, this benefits the common case for any code using the global locale, such as construction/destruction of iostream objects. All these updates are done inside libstdc++.so so there's no need to worry about users' objects having inlined old versions of the code which still update the reference count for the classic locale. PR libstdc++/59439 * src/c++98/locale.cc (locale::locale(const locale&)): Bypass reference count updates for the classic locale. (locale::~locale()): Likewise. (locale::operator=(const locale&)): Likewise. * src/c++98/locale_init.cc (locale::locale()): Likewise. (locale::global(const locale&)): Likewise. From-SVN: r264811 --- libstdc++-v3/ChangeLog | 10 ++++++++++ libstdc++-v3/src/c++98/locale.cc | 16 ++++++++++++---- libstdc++-v3/src/c++98/locale_init.cc | 9 ++++----- 3 files changed, 26 insertions(+), 9 deletions(-) diff --git a/libstdc++-v3/ChangeLog b/libstdc++-v3/ChangeLog index fe0fbf7bbdc..84e61ca955c 100644 --- a/libstdc++-v3/ChangeLog +++ b/libstdc++-v3/ChangeLog @@ -1,3 +1,13 @@ +2018-10-03 Jonathan Wakely + + PR libstdc++/59439 + * src/c++98/locale.cc (locale::locale(const locale&)): Bypass + reference count updates for the classic locale. + (locale::~locale()): Likewise. + (locale::operator=(const locale&)): Likewise. + * src/c++98/locale_init.cc (locale::locale()): Likewise. + (locale::global(const locale&)): Likewise. + 2018-10-03 François Dumont * include/debug/map.h diff --git a/libstdc++-v3/src/c++98/locale.cc b/libstdc++-v3/src/c++98/locale.cc index 148bf59658e..fe06d297039 100644 --- a/libstdc++-v3/src/c++98/locale.cc +++ b/libstdc++-v3/src/c++98/locale.cc @@ -77,7 +77,10 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION locale::locale(const locale& __other) throw() : _M_impl(__other._M_impl) - { _M_impl->_M_add_reference(); } + { + if (_M_impl != _S_classic) + _M_impl->_M_add_reference(); + } // This is used to initialize global and classic locales, and // assumes that the _Impl objects are constructed correctly. @@ -86,7 +89,10 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION { } locale::~locale() throw() - { _M_impl->_M_remove_reference(); } + { + if (_M_impl != _S_classic) + _M_impl->_M_remove_reference(); + } bool locale::operator==(const locale& __rhs) const throw() @@ -112,8 +118,10 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION const locale& locale::operator=(const locale& __other) throw() { - __other._M_impl->_M_add_reference(); - _M_impl->_M_remove_reference(); + if (__other._M_impl != _S_classic) + __other._M_impl->_M_add_reference(); + if (_M_impl != _S_classic) + _M_impl->_M_remove_reference(); _M_impl = __other._M_impl; return *this; } diff --git a/libstdc++-v3/src/c++98/locale_init.cc b/libstdc++-v3/src/c++98/locale_init.cc index c9078c015c3..b580a9f9d58 100644 --- a/libstdc++-v3/src/c++98/locale_init.cc +++ b/libstdc++-v3/src/c++98/locale_init.cc @@ -257,9 +257,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION // fall back to lock protected access to both _S_global and // its reference count. _M_impl = _S_global; - if (_M_impl == _S_classic) - _M_impl->_M_add_reference(); - else + if (_M_impl != _S_classic) { __gnu_cxx::__scoped_lock sentry(get_locale_mutex()); _S_global->_M_add_reference(); @@ -275,7 +273,8 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION { __gnu_cxx::__scoped_lock sentry(get_locale_mutex()); __old = _S_global; - __other._M_impl->_M_add_reference(); + if (__other._M_impl != _S_classic) + __other._M_impl->_M_add_reference(); _S_global = __other._M_impl; const string __other_name = __other.name(); if (__other_name != "*") @@ -284,7 +283,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION // Reference count sanity check: one reference removed for the // subsition of __other locale, one added by return-by-value. Net - // difference: zero. When the returned locale object's destrutor + // difference: zero. When the returned locale object's destructor // is called, then the reference count is decremented and possibly // destroyed. return locale(__old);