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Merged
StephanTLavavej merged 1 commit into from
Jun 14, 2025
Merged

<semaphore>: use steady_clock #5575

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14 changes: 4 additions & 10 deletions stl/inc/semaphore
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Original file line number Diff line number Diff line change
Expand Up @@ -29,12 +29,6 @@ _STL_DISABLE_CLANG_WARNINGS

_STD_BEGIN

template <class _Rep, class _Period>
_NODISCARD unsigned long long _Semaphore_deadline(const chrono::duration<_Rep, _Period>& _Rel_time) {
return __std_atomic_wait_get_deadline(
chrono::duration_cast<chrono::duration<unsigned long long, milli>>(_Rel_time).count());
}

template <class _Clock, class _Duration>
_NODISCARD unsigned long _Semaphore_remaining_timeout(const chrono::time_point<_Clock, _Duration>& _Abs_time) {
const auto _Now = _Clock::now();
Expand Down Expand Up @@ -145,11 +139,11 @@ public:

template <class _Rep, class _Period>
_NODISCARD_TRY_CHANGE_STATE bool try_acquire_for(const chrono::duration<_Rep, _Period>& _Rel_time) {
auto _Deadline = _Semaphore_deadline(_Rel_time);
auto _Deadline = _STD chrono::steady_clock::now() + _Rel_time;
ptrdiff_t _Current = _Counter.load(memory_order_relaxed);
for (;;) {
while (_Current == 0) {
const auto _Remaining_timeout = __std_atomic_wait_get_remaining_timeout(_Deadline);
const auto _Remaining_timeout = _Semaphore_remaining_timeout(_Deadline);
if (_Remaining_timeout == 0) {
return false;
}
Expand Down Expand Up @@ -257,7 +251,7 @@ public:

template <class _Rep, class _Period>
_NODISCARD_TRY_CHANGE_STATE bool try_acquire_for(const chrono::duration<_Rep, _Period>& _Rel_time) {
auto _Deadline = _Semaphore_deadline(_Rel_time);
auto _Deadline = _STD chrono::steady_clock::now() + _Rel_time;
for (;;) {
// "happens after release" ordering is provided by this exchange, so loads and waits can be relaxed
// TRANSITION, GH-1133: should be memory_order_acquire
Expand All @@ -267,7 +261,7 @@ public:
}
_STL_VERIFY(_Prev == 0, "Invariant: semaphore counter is non-negative and doesn't exceed max(), "
"possibly caused by memory corruption");
const auto _Remaining_timeout = __std_atomic_wait_get_remaining_timeout(_Deadline);
const auto _Remaining_timeout = _Semaphore_remaining_timeout(_Deadline);
if (_Remaining_timeout == 0) {
return false;
}
Expand Down
6 changes: 0 additions & 6 deletions stl/inc/xatomic_wait.h
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Expand Up @@ -40,12 +40,6 @@ int __stdcall __std_atomic_wait_indirect(const void* _Storage, void* _Comparand,
void __stdcall __std_atomic_notify_one_indirect(const void* _Storage) noexcept;
void __stdcall __std_atomic_notify_all_indirect(const void* _Storage) noexcept;

// These functions convert a duration into a time point in order to tolerate spurious wakes in atomic wait, and then
// convert back from the time point to individual wait attempts (which are limited by DWORD milliseconds to a length of
// ~49 days)
unsigned long long __stdcall __std_atomic_wait_get_deadline(unsigned long long _Timeout) noexcept;
unsigned long __stdcall __std_atomic_wait_get_remaining_timeout(unsigned long long _Deadline) noexcept;

} // extern "C"

#pragma pop_macro("new")
Expand Down
2 changes: 2 additions & 0 deletions stl/src/atomic_wait.cpp
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Expand Up @@ -177,6 +177,7 @@ int __stdcall __std_atomic_wait_indirect(const void* _Storage, void* _Comparand,
}
}

// TRANSITION, ABI: preserved for binary compatibility
unsigned long long __stdcall __std_atomic_wait_get_deadline(const unsigned long long _Timeout) noexcept {
if (_Timeout == _Atomic_wait_no_deadline) {
return _Atomic_wait_no_deadline;
Expand All @@ -185,6 +186,7 @@ unsigned long long __stdcall __std_atomic_wait_get_deadline(const unsigned long
}
}

// TRANSITION, ABI: preserved for binary compatibility
unsigned long __stdcall __std_atomic_wait_get_remaining_timeout(unsigned long long _Deadline) noexcept {
static_assert(__std_atomic_wait_no_timeout == INFINITE,
"__std_atomic_wait_no_timeout is passed directly to underlying API, so should match it");
Expand Down