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<locale>: Double-checked locking for locale::classic #3048

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merged 8 commits into from
Oct 27, 2022
Merged

<locale>: Double-checked locking for locale::classic #3048

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1446049
Double-checked locking for locale::classic
MattStephanson Aug 20, 2022
e9222c6
Replace `Interlocked` calls with intrinsic load/store and barriers.
MattStephanson Aug 31, 2022
a4dd979
always use locking for `/clr:pure`
MattStephanson Sep 3, 2022
8890971
Merge branch 'main' into classic-locale-locking
MattStephanson Oct 26, 2022
2907701
review feedback
MattStephanson Oct 26, 2022
5b944d5
D'oh
MattStephanson Oct 26, 2022
6519e24
Merge branch 'main' into classic-locale-locking
StephanTLavavej Oct 26, 2022
6160021
Add a benchmark. Also sort the list of benchmarks.
StephanTLavavej Oct 26, 2022
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44 changes: 40 additions & 4 deletions stl/src/locale0.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -135,8 +135,36 @@ __PURE_APPDOMAIN_GLOBAL locale::id ctype<unsigned short>::id(0);

__PURE_APPDOMAIN_GLOBAL locale::id codecvt<unsigned short, char, mbstate_t>::id(0);

#define _Compiler_barrier() _STL_DISABLE_DEPRECATED_WARNING _ReadWriteBarrier() _STL_RESTORE_DEPRECATED_WARNING

#if defined(_M_ARM) || defined(_M_ARM64) || defined(_M_ARM64EC)
#define _Memory_barrier() __dmb(0xB) // inner shared data memory barrier
#define _Compiler_or_memory_barrier() _Memory_barrier()
#elif defined(_M_IX86) || defined(_M_X64)
// x86/x64 hardware only emits memory barriers inside _Interlocked intrinsics
#define _Compiler_or_memory_barrier() _Compiler_barrier()
#else // ^^^ x86/x64 / unsupported hardware vvv
#error Unsupported hardware
#endif // hardware
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_MRTIMP2_PURE const locale& __CLRCALL_PURE_OR_CDECL locale::classic() { // get reference to "C" locale
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_Init();
const auto mem = reinterpret_cast<const intptr_t*>(&locale::_Locimp::_Clocptr);
intptr_t as_bytes;
#ifdef _WIN64
#ifdef _M_ARM
as_bytes = __ldrexd(_Mem);
#else
as_bytes = __iso_volatile_load64(mem);
#endif
#else // ^^^ _WIN64 / !_WIN64 vvv
as_bytes = __iso_volatile_load32(mem);
#endif // ^^^ !_WIN64 ^^^
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_Compiler_or_memory_barrier();
const auto ptr = reinterpret_cast<locale::_Locimp*>(as_bytes);
if (ptr == nullptr) {
_Init();
}

return classic_locale;
}

Expand All @@ -157,9 +185,17 @@ _MRTIMP2_PURE locale::_Locimp* __CLRCALL_PURE_OR_CDECL locale::_Init(bool _Do_in
ptr->_Catmask = all; // set current locale to "C"
ptr->_Name = "C";

_Locimp::_Clocptr = ptr; // set classic to match
_Locimp::_Clocptr->_Incref();
::new (&classic_locale) locale(_Locimp::_Clocptr);
// set classic to match
ptr->_Incref();
::new (&classic_locale) locale(ptr);
const auto mem = reinterpret_cast<volatile intptr_t*>(&locale::_Locimp::_Clocptr);
const auto as_bytes = reinterpret_cast<intptr_t>(ptr);
_Compiler_or_memory_barrier();
#ifdef _WIN64
__iso_volatile_store64(mem, as_bytes);
#else
__iso_volatile_store32(mem, as_bytes);
#endif
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}

if (_Do_incref) {
Expand Down