STL/stl/inc/latch

102 строки
3.2 KiB
C++

// latch standard header
// Copyright (c) Microsoft Corporation.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
#pragma once
#ifndef _LATCH_
#define _LATCH_
#include <yvals.h>
#if _STL_COMPILER_PREPROCESSOR
#ifdef _M_CEE_PURE
#error <latch> is not supported when compiling with /clr:pure.
#endif // _M_CEE_PURE
#if !_HAS_CXX20
#pragma message("The contents of <latch> are available only with C++20 or later.")
#else // ^^^ !_HAS_CXX20 / _HAS_CXX20 vvv
#include <atomic>
#include <climits>
#pragma pack(push, _CRT_PACKING)
#pragma warning(push, _STL_WARNING_LEVEL)
#pragma warning(disable : _STL_DISABLED_WARNINGS)
_STL_DISABLE_CLANG_WARNINGS
#pragma push_macro("new")
#undef new
_STD_BEGIN
class latch {
public:
_NODISCARD static constexpr ptrdiff_t(max)() noexcept {
return (1ULL << (sizeof(ptrdiff_t) * CHAR_BIT - 1)) - 1;
}
constexpr explicit latch(const ptrdiff_t _Expected) noexcept /* strengthened */ : _Counter{_Expected} {
_STL_VERIFY(_Expected >= 0, "Precondition: expected >= 0 (N4861 [thread.latch.class]/4)");
}
latch(const latch&) = delete;
latch& operator=(const latch&) = delete;
void count_down(const ptrdiff_t _Update = 1) noexcept /* strengthened */ {
_STL_VERIFY(_Update >= 0, "Precondition: update >= 0 (N4861 [thread.latch.class]/7)");
// TRANSITION, GH-1133: should be memory_order_release
const ptrdiff_t _Current = _Counter.fetch_sub(_Update) - _Update;
if (_Current == 0) {
_Counter.notify_all();
} else {
_STL_VERIFY(_Current >= 0, "Precondition: update <= counter (N4861 [thread.latch.class]/7)");
}
}
_NODISCARD bool try_wait() const noexcept {
// TRANSITION, GH-1133: should be memory_order_acquire
return _Counter.load() == 0;
}
void wait() const noexcept /* strengthened */ {
for (;;) {
// TRANSITION, GH-1133: should be memory_order_acquire
const ptrdiff_t _Current = _Counter.load();
if (_Current == 0) {
return;
} else {
_STL_VERIFY(_Current > 0, "Invariant counter >= 0, possibly caused by preconditions violation "
"(N4861 [thread.latch.class]/7)");
}
_Counter.wait(_Current, memory_order_relaxed);
}
}
void arrive_and_wait(const ptrdiff_t _Update = 1) noexcept /* strengthened */ {
_STL_VERIFY(_Update >= 0, "Precondition: update >= 0 (N4861 [thread.latch.class]/7)");
// TRANSITION, GH-1133: should be memory_order_acq_rel
const ptrdiff_t _Current = _Counter.fetch_sub(_Update) - _Update;
if (_Current == 0) {
_Counter.notify_all();
} else {
_STL_VERIFY(_Current > 0, "Precondition: update <= counter (N4861 [thread.latch.class]/7)");
_Counter.wait(_Current, memory_order_relaxed);
wait();
}
}
private:
atomic<ptrdiff_t> _Counter;
};
_STD_END
#pragma pop_macro("new")
_STL_RESTORE_CLANG_WARNINGS
#pragma warning(pop)
#pragma pack(pop)
#endif // ^^^ _HAS_CXX20 ^^^
#endif // _STL_COMPILER_PREPROCESSOR
#endif // _LATCH_