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libstdc++: Use __is_single_threaded in locale initialization 

This replaces a __gthread_active_p() check with __is_single_threaded()
so that std::locale initialization doesn't use __gthread_once if it
happens before the first thread is created.

This means that _S_initialize_once() might now be called twice instead
of only once, because if __is_single_threaded() changes to false then we
will do the __gthread_once call even if _S_initialize_once() was already
called. Add a check to _S_initialize_once() and return immediately if
it is the second call.

Also use __builtin_expect to _S_initialize, as the branch will be taken
at most once in the lifetime of the program.

libstdc++-v3/ChangeLog:

	* src/c++98/locale_init.cc (_S_initialize_once): Check if
	initialization has already been done.
	(_S_initialize): Replace __gthread_active_p with
	__is_single_threaded. Use __builtin_expect.
This commit is contained in:
Jonathan Wakely 2021-11-19 12:26:49 +00:00
parent 1f8d01eb14
commit 5faf1c8c7a
1 changed files with 9 additions and 2 deletions
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11
libstdc++-v3/src/c++98/locale_init.cc
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@ -31,6 +31,7 @@
#include <cctype>
#include <cwctype> // For towupper, etc.
#include <locale>
#include <ext/atomicity.h>
#include <ext/concurrence.h>
#if _GLIBCXX_USE_DUAL_ABI
@ -321,6 +322,12 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
void
locale::_S_initialize_once() throw()
{
// Need to check this because we could get called once from _S_initialize()
// when the program is single-threaded, and then again (via __gthread_once)
// when it's multi-threaded.
if (_S_classic)
return;
// 2 references.
// One reference for _S_classic, one for _S_global
_S_classic = new (&c_locale_impl) _Impl(2);
@ -332,10 +339,10 @@ _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)
if (__builtin_expect(!_S_classic, 0))
_S_initialize_once();
}