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PR libstdc++/91057 set locale:🆔:_M_index atomically

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If two threads see _M_index==0 concurrently they will both try to set
it, potentially storing the facet at two different indices in the array.

Either set the _M_index data member using an atomic compare-exchange
operation or while holding a mutex.

Also move the LONG_DOUBLE_COMPAT code into a separate function to remove
the visual noise it creates.

	PR libstdc++/91057
	* src/c++98/locale.cc (locale:🆔:_M_id()) [__GTHREADS]: Use atomic
	compare-exchange or double-checked lock to ensure only one thread sets
	the _M_index variable.
	[_GLIBCXX_LONG_DOUBLE_COMPAT]: Call find_ldbl_sync_facet to detect
	facets that share another facet's ID.
	[_GLIBCXX_LONG_DOUBLE_COMPAT] (find_ldbl_sync_facet): New function.

From-SVN: r276762
This commit is contained in:
Jonathan Wakely 2019-10-09 16:59:56 +01:00 committed by Jonathan Wakely
parent 4a8841c041
commit cc386cf233
2 changed files with 62 additions and 18 deletions
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8
libstdc++-v3/ChangeLog
View File

@ -1,5 +1,13 @@
2019-10-09 Jonathan Wakely <jwakely@redhat.com>
PR libstdc++/91057
* src/c++98/locale.cc (locale::id::_M_id()) [__GTHREADS]: Use atomic
compare-exchange or double-checked lock to ensure only one thread sets
the _M_index variable.
[_GLIBCXX_LONG_DOUBLE_COMPAT]: Call find_ldbl_sync_facet to detect
facets that share another facet's ID.
[_GLIBCXX_LONG_DOUBLE_COMPAT] (find_ldbl_sync_facet): New function.
PR libstdc++/78552
* src/c++98/locale_init.cc (locale::classic()): Do not construct a new
locale object for every call.

72
libstdc++-v3/src/c++98/locale.cc
View File

@ -474,6 +474,30 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
// Definitions for static const data members of locale::id
_Atomic_word locale::id::_S_refcount; // init'd to 0 by linker
// XXX GLIBCXX_ABI Deprecated
#ifdef _GLIBCXX_LONG_DOUBLE_COMPAT
namespace {
inline locale::id*
find_ldbl_sync_facet(locale::id* __idp)
{
# define _GLIBCXX_SYNC_ID(facet, mangled) \
if (__idp == &::mangled) \
return &facet::id
_GLIBCXX_SYNC_ID (num_get<char>, _ZNSt7num_getIcSt19istreambuf_iteratorIcSt11char_traitsIcEEE2idE);
_GLIBCXX_SYNC_ID (num_put<char>, _ZNSt7num_putIcSt19ostreambuf_iteratorIcSt11char_traitsIcEEE2idE);
_GLIBCXX_SYNC_ID (money_get<char>, _ZNSt9money_getIcSt19istreambuf_iteratorIcSt11char_traitsIcEEE2idE);
_GLIBCXX_SYNC_ID (money_put<char>, _ZNSt9money_putIcSt19ostreambuf_iteratorIcSt11char_traitsIcEEE2idE);
# ifdef _GLIBCXX_USE_WCHAR_T
_GLIBCXX_SYNC_ID (num_get<wchar_t>, _ZNSt7num_getIwSt19istreambuf_iteratorIwSt11char_traitsIwEEE2idE);
_GLIBCXX_SYNC_ID (num_put<wchar_t>, _ZNSt7num_putIwSt19ostreambuf_iteratorIwSt11char_traitsIwEEE2idE);
_GLIBCXX_SYNC_ID (money_get<wchar_t>, _ZNSt9money_getIwSt19istreambuf_iteratorIwSt11char_traitsIwEEE2idE);
_GLIBCXX_SYNC_ID (money_put<wchar_t>, _ZNSt9money_putIwSt19ostreambuf_iteratorIwSt11char_traitsIwEEE2idE);
# endif
}
} // namespace
#endif
size_t
locale::id::_M_id() const throw()
{
@ -481,26 +505,38 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
{
// XXX GLIBCXX_ABI Deprecated
#ifdef _GLIBCXX_LONG_DOUBLE_COMPAT
locale::id *f = 0;
# define _GLIBCXX_SYNC_ID(facet, mangled) \
if (this == &::mangled) \
f = &facet::id
_GLIBCXX_SYNC_ID (num_get<char>, _ZNSt7num_getIcSt19istreambuf_iteratorIcSt11char_traitsIcEEE2idE);
_GLIBCXX_SYNC_ID (num_put<char>, _ZNSt7num_putIcSt19ostreambuf_iteratorIcSt11char_traitsIcEEE2idE);
_GLIBCXX_SYNC_ID (money_get<char>, _ZNSt9money_getIcSt19istreambuf_iteratorIcSt11char_traitsIcEEE2idE);
_GLIBCXX_SYNC_ID (money_put<char>, _ZNSt9money_putIcSt19ostreambuf_iteratorIcSt11char_traitsIcEEE2idE);
# ifdef _GLIBCXX_USE_WCHAR_T
_GLIBCXX_SYNC_ID (num_get<wchar_t>, _ZNSt7num_getIwSt19istreambuf_iteratorIwSt11char_traitsIwEEE2idE);
_GLIBCXX_SYNC_ID (num_put<wchar_t>, _ZNSt7num_putIwSt19ostreambuf_iteratorIwSt11char_traitsIwEEE2idE);
_GLIBCXX_SYNC_ID (money_get<wchar_t>, _ZNSt9money_getIwSt19istreambuf_iteratorIwSt11char_traitsIwEEE2idE);
_GLIBCXX_SYNC_ID (money_put<wchar_t>, _ZNSt9money_putIwSt19ostreambuf_iteratorIwSt11char_traitsIwEEE2idE);
# endif
if (f)
_M_index = 1 + f->_M_id();
if (locale::id* f = find_ldbl_sync_facet(this))
{
const size_t sync_id = f->_M_id();
_M_index = 1 + sync_id;
return sync_id;
}
#endif
#ifdef __GTHREADS
if (__gthread_active_p())
{
if (__atomic_always_lock_free(sizeof(_M_index), &_M_index))
{
const _Atomic_word next
= 1 + __gnu_cxx::__exchange_and_add(&_S_refcount, 1);
size_t expected = 0;
__atomic_compare_exchange_n(&_M_index, &expected, next,
/* weak = */ false,
/* success = */ __ATOMIC_ACQ_REL,
/* failure = */ __ATOMIC_ACQUIRE);
}
else
{
static __gnu_cxx::__mutex m;
__gnu_cxx::__scoped_lock l(m);
if (!_M_index)
_M_index = ++_S_refcount;
}
}
else
#endif
_M_index = 1 + __gnu_cxx::__exchange_and_add_dispatch(&_S_refcount,
1);
_M_index = ++_S_refcount; // single-threaded case
}
return _M_index - 1;
}