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* [gcc r11-5314] libstdc++: Use __libc_single_threaded for locale initialization
@ 2020-11-24 14:59 Jonathan Wakely
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From: Jonathan Wakely @ 2020-11-24 14:59 UTC (permalink / raw)
To: gcc-cvs, libstdc++-cvs
https://gcc.gnu.org/g:e253d36214015ed10ffd335e3628ccaac22dd5c7
commit r11-5314-ge253d36214015ed10ffd335e3628ccaac22dd5c7
Author: Jonathan Wakely <jwakely@redhat.com>
Date: Tue Nov 24 12:29:30 2020 +0000
libstdc++: Use __libc_single_threaded for locale initialization
Most initialization of locales and facets happens before main() during
startup, when the program is likely to only have one thread. By using
the new __gnu_cxx::__is_single_threaded() function instead of checking
__gthread_active_p() we can avoid using pthread_once or atomics for the
common case.
That said, I'm not sure why we don't just use a local static variable
instead, as __cxa_guard_acquire() already optimizes for the
single-threaded case:
static const bool init = (_S_initialize_once(), true);
I'll revisit that for GCC 12.
libstdc++-v3/ChangeLog:
* src/c++98/locale.cc (locale::facet::_S_get_c_locale())
(locale::id::_M_id() const): Use __is_single_threaded.
* src/c++98/locale_init.cc (locale::_S_initialize()):
Likewise.
Diff:
---
libstdc++-v3/src/c++98/locale.cc | 4 ++--
libstdc++-v3/src/c++98/locale_init.cc | 2 +-
2 files changed, 3 insertions(+), 3 deletions(-)
diff --git a/libstdc++-v3/src/c++98/locale.cc b/libstdc++-v3/src/c++98/locale.cc
index 06422412039..9b3fc351515 100644
--- a/libstdc++-v3/src/c++98/locale.cc
+++ b/libstdc++-v3/src/c++98/locale.cc
@@ -214,7 +214,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
locale::facet::_S_get_c_locale()
{
#ifdef __GTHREADS
- if (__gthread_active_p())
+ if (!__gnu_cxx::__is_single_threaded())
__gthread_once(&_S_once, _S_initialize_once);
else
#endif
@@ -515,7 +515,7 @@ namespace {
#endif
#ifdef __GTHREADS
- if (__gthread_active_p())
+ if (!__gnu_cxx::__is_single_threaded())
{
if (__atomic_always_lock_free(sizeof(_M_index), &_M_index))
{
diff --git a/libstdc++-v3/src/c++98/locale_init.cc b/libstdc++-v3/src/c++98/locale_init.cc
index c3841ccbd3c..fc8416ba01a 100644
--- a/libstdc++-v3/src/c++98/locale_init.cc
+++ b/libstdc++-v3/src/c++98/locale_init.cc
@@ -320,7 +320,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
locale::_S_initialize()
{
#ifdef __GTHREADS
- if (__gthread_active_p())
+ if (!__gnu_cxx::__is_single_threaded())
__gthread_once(&_S_once, _S_initialize_once);
#endif
if (!_S_classic)
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