[libc++] refactor cxx_atomic_wait to make it reusable for atomic_ref (#81427)
The goal of this patch is to make `atomic`'s wait functions to be reusable by `atomic_ref`. https://github.com/llvm/llvm-project/pull/76647 First, this patch is built on top of https://github.com/llvm/llvm-project/pull/80596 , to reduce the future merge conflicts. This patch made the following functions as "API"s to be used by `atomic`, `atomic_flag`, `semaphore`, `latch`, `atomic_ref` ``` __atomic_wait __atomic_wait_unless __atomic_notify_one __atomic_notify_all ``` These functions are made generic to support `atomic` type and `atomic_ref`. There are two customisation points. ``` // How to load the value from the given type (with a memory order) __atomic_load ``` ``` // what is the contention address that the platform `wait` function is going to monitor __atomic_contention_address ``` For `atomic_ref` (not implemented in this patch), the `load` and `address` function will be different, because - it does not use the "atomic abstraction layer" so the `load` operation will be some gcc builtin - the contention address will be the user's actual type that the `atomic_ref` is pointing to
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@ -104,24 +104,20 @@ struct __atomic_base // false
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_LIBCPP_AVAILABILITY_SYNC _LIBCPP_HIDE_FROM_ABI void wait(_Tp __v, memory_order __m = memory_order_seq_cst) const
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volatile _NOEXCEPT {
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std::__cxx_atomic_wait(std::addressof(__a_), __v, __m);
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std::__atomic_wait(*this, __v, __m);
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}
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_LIBCPP_AVAILABILITY_SYNC _LIBCPP_HIDE_FROM_ABI void
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wait(_Tp __v, memory_order __m = memory_order_seq_cst) const _NOEXCEPT {
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std::__cxx_atomic_wait(std::addressof(__a_), __v, __m);
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std::__atomic_wait(*this, __v, __m);
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}
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_LIBCPP_AVAILABILITY_SYNC _LIBCPP_HIDE_FROM_ABI void notify_one() volatile _NOEXCEPT {
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std::__cxx_atomic_notify_one(std::addressof(__a_));
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}
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_LIBCPP_AVAILABILITY_SYNC _LIBCPP_HIDE_FROM_ABI void notify_one() _NOEXCEPT {
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std::__cxx_atomic_notify_one(std::addressof(__a_));
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std::__atomic_notify_one(*this);
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}
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_LIBCPP_AVAILABILITY_SYNC _LIBCPP_HIDE_FROM_ABI void notify_one() _NOEXCEPT { std::__atomic_notify_one(*this); }
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_LIBCPP_AVAILABILITY_SYNC _LIBCPP_HIDE_FROM_ABI void notify_all() volatile _NOEXCEPT {
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std::__cxx_atomic_notify_all(std::addressof(__a_));
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}
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_LIBCPP_AVAILABILITY_SYNC _LIBCPP_HIDE_FROM_ABI void notify_all() _NOEXCEPT {
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std::__cxx_atomic_notify_all(std::addressof(__a_));
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std::__atomic_notify_all(*this);
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}
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_LIBCPP_AVAILABILITY_SYNC _LIBCPP_HIDE_FROM_ABI void notify_all() _NOEXCEPT { std::__atomic_notify_all(*this); }
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#if _LIBCPP_STD_VER >= 20
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_LIBCPP_HIDE_FROM_ABI constexpr __atomic_base() noexcept(is_nothrow_default_constructible_v<_Tp>) : __a_(_Tp()) {}
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@ -200,6 +196,32 @@ struct __atomic_base<_Tp, true> : public __atomic_base<_Tp, false> {
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_LIBCPP_HIDE_FROM_ABI _Tp operator^=(_Tp __op) _NOEXCEPT { return fetch_xor(__op) ^ __op; }
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};
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// Here we need _IsIntegral because the default template argument is not enough
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// e.g __atomic_base<int> is __atomic_base<int, true>, which inherits from
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// __atomic_base<int, false> and the caller of the wait function is
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// __atomic_base<int, false>. So specializing __atomic_base<_Tp> does not work
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template <class _Tp, bool _IsIntegral>
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struct __atomic_waitable_traits<__atomic_base<_Tp, _IsIntegral> > {
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static _LIBCPP_HIDE_FROM_ABI _Tp __atomic_load(const __atomic_base<_Tp, _IsIntegral>& __a, memory_order __order) {
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return __a.load(__order);
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}
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static _LIBCPP_HIDE_FROM_ABI _Tp
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__atomic_load(const volatile __atomic_base<_Tp, _IsIntegral>& __this, memory_order __order) {
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return __this.load(__order);
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}
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static _LIBCPP_HIDE_FROM_ABI const __cxx_atomic_impl<_Tp>*
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__atomic_contention_address(const __atomic_base<_Tp, _IsIntegral>& __a) {
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return std::addressof(__a.__a_);
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}
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static _LIBCPP_HIDE_FROM_ABI const volatile __cxx_atomic_impl<_Tp>*
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__atomic_contention_address(const volatile __atomic_base<_Tp, _IsIntegral>& __this) {
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return std::addressof(__this.__a_);
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}
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};
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_LIBCPP_END_NAMESPACE_STD
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#endif // _LIBCPP___ATOMIC_ATOMIC_BASE_H
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@ -16,6 +16,7 @@
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#include <__availability>
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#include <__chrono/duration.h>
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#include <__config>
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#include <__memory/addressof.h>
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#include <__thread/support.h>
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#include <cstdint>
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@ -50,20 +51,20 @@ struct atomic_flag {
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_LIBCPP_AVAILABILITY_SYNC _LIBCPP_HIDE_FROM_ABI void wait(bool __v, memory_order __m = memory_order_seq_cst) const
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volatile _NOEXCEPT {
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__cxx_atomic_wait(&__a_, _LIBCPP_ATOMIC_FLAG_TYPE(__v), __m);
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std::__atomic_wait(*this, _LIBCPP_ATOMIC_FLAG_TYPE(__v), __m);
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}
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_LIBCPP_AVAILABILITY_SYNC _LIBCPP_HIDE_FROM_ABI void
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wait(bool __v, memory_order __m = memory_order_seq_cst) const _NOEXCEPT {
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__cxx_atomic_wait(&__a_, _LIBCPP_ATOMIC_FLAG_TYPE(__v), __m);
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std::__atomic_wait(*this, _LIBCPP_ATOMIC_FLAG_TYPE(__v), __m);
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}
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_LIBCPP_AVAILABILITY_SYNC _LIBCPP_HIDE_FROM_ABI void notify_one() volatile _NOEXCEPT {
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__cxx_atomic_notify_one(&__a_);
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std::__atomic_notify_one(*this);
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}
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_LIBCPP_AVAILABILITY_SYNC _LIBCPP_HIDE_FROM_ABI void notify_one() _NOEXCEPT { __cxx_atomic_notify_one(&__a_); }
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_LIBCPP_AVAILABILITY_SYNC _LIBCPP_HIDE_FROM_ABI void notify_one() _NOEXCEPT { std::__atomic_notify_one(*this); }
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_LIBCPP_AVAILABILITY_SYNC _LIBCPP_HIDE_FROM_ABI void notify_all() volatile _NOEXCEPT {
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__cxx_atomic_notify_all(&__a_);
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std::__atomic_notify_all(*this);
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}
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_LIBCPP_AVAILABILITY_SYNC _LIBCPP_HIDE_FROM_ABI void notify_all() _NOEXCEPT { __cxx_atomic_notify_all(&__a_); }
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_LIBCPP_AVAILABILITY_SYNC _LIBCPP_HIDE_FROM_ABI void notify_all() _NOEXCEPT { std::__atomic_notify_all(*this); }
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#if _LIBCPP_STD_VER >= 20
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_LIBCPP_HIDE_FROM_ABI constexpr atomic_flag() _NOEXCEPT : __a_(false) {}
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@ -78,6 +79,28 @@ struct atomic_flag {
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atomic_flag& operator=(const atomic_flag&) volatile = delete;
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};
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template <>
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struct __atomic_waitable_traits<atomic_flag> {
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static _LIBCPP_HIDE_FROM_ABI _LIBCPP_ATOMIC_FLAG_TYPE __atomic_load(const atomic_flag& __a, memory_order __order) {
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return std::__cxx_atomic_load(&__a.__a_, __order);
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}
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static _LIBCPP_HIDE_FROM_ABI _LIBCPP_ATOMIC_FLAG_TYPE
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__atomic_load(const volatile atomic_flag& __a, memory_order __order) {
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return std::__cxx_atomic_load(&__a.__a_, __order);
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}
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static _LIBCPP_HIDE_FROM_ABI const __cxx_atomic_impl<_LIBCPP_ATOMIC_FLAG_TYPE>*
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__atomic_contention_address(const atomic_flag& __a) {
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return std::addressof(__a.__a_);
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}
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static _LIBCPP_HIDE_FROM_ABI const volatile __cxx_atomic_impl<_LIBCPP_ATOMIC_FLAG_TYPE>*
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__atomic_contention_address(const volatile atomic_flag& __a) {
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return std::addressof(__a.__a_);
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}
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};
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inline _LIBCPP_HIDE_FROM_ABI bool atomic_flag_test(const volatile atomic_flag* __o) _NOEXCEPT { return __o->test(); }
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inline _LIBCPP_HIDE_FROM_ABI bool atomic_flag_test(const atomic_flag* __o) _NOEXCEPT { return __o->test(); }
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@ -18,7 +18,11 @@
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#include <__memory/addressof.h>
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#include <__thread/poll_with_backoff.h>
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#include <__thread/support.h>
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#include <__type_traits/conjunction.h>
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#include <__type_traits/decay.h>
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#include <__type_traits/invoke.h>
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#include <__type_traits/void_t.h>
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#include <__utility/declval.h>
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#include <cstring>
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#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
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@ -27,15 +31,40 @@
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_LIBCPP_BEGIN_NAMESPACE_STD
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template <class _Atp, class _Poll>
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struct __libcpp_atomic_wait_poll_impl {
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_Atp* __a_;
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// The customisation points to enable the following functions:
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// - __atomic_wait
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// - __atomic_wait_unless
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// - __atomic_notify_one
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// - __atomic_notify_all
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// Note that std::atomic<T>::wait was back-ported to C++03
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// The below implementations look ugly to support C++03
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template <class _Tp, class = void>
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struct __atomic_waitable_traits {
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template <class _AtomicWaitable>
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static void __atomic_load(_AtomicWaitable&&, memory_order) = delete;
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template <class _AtomicWaitable>
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static void __atomic_contention_address(_AtomicWaitable&&) = delete;
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};
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template <class _Tp, class = void>
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struct __atomic_waitable : false_type {};
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template <class _Tp>
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struct __atomic_waitable< _Tp,
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__void_t<decltype(__atomic_waitable_traits<__decay_t<_Tp> >::__atomic_load(
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std::declval<const _Tp&>(), std::declval<memory_order>())),
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decltype(__atomic_waitable_traits<__decay_t<_Tp> >::__atomic_contention_address(
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std::declval<const _Tp&>()))> > : true_type {};
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template <class _AtomicWaitable, class _Poll>
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struct __atomic_wait_poll_impl {
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const _AtomicWaitable& __a_;
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_Poll __poll_;
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memory_order __order_;
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_LIBCPP_AVAILABILITY_SYNC
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_LIBCPP_HIDE_FROM_ABI bool operator()() const {
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auto __current_val = std::__cxx_atomic_load(__a_, __order_);
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auto __current_val = __atomic_waitable_traits<__decay_t<_AtomicWaitable> >::__atomic_load(__a_, __order_);
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return __poll_(__current_val);
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}
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};
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@ -56,42 +85,45 @@ __libcpp_atomic_monitor(__cxx_atomic_contention_t const volatile*);
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_LIBCPP_AVAILABILITY_SYNC _LIBCPP_EXPORTED_FROM_ABI void
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__libcpp_atomic_wait(__cxx_atomic_contention_t const volatile*, __cxx_contention_t);
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template <class _Atp, class _Poll>
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struct __libcpp_atomic_wait_backoff_impl {
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_Atp* __a_;
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template <class _AtomicWaitable, class _Poll>
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struct __atomic_wait_backoff_impl {
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const _AtomicWaitable& __a_;
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_Poll __poll_;
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memory_order __order_;
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using __waitable_traits = __atomic_waitable_traits<__decay_t<_AtomicWaitable> >;
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_LIBCPP_AVAILABILITY_SYNC
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_LIBCPP_HIDE_FROM_ABI bool
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__poll_or_get_monitor(__cxx_atomic_contention_t const volatile*, __cxx_contention_t& __monitor) const {
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// In case the atomic can be waited on directly, the monitor value is just
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// the value of the atomic.
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__update_monitor_val_and_poll(__cxx_atomic_contention_t const volatile*, __cxx_contention_t& __monitor_val) const {
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// In case the contention type happens to be __cxx_atomic_contention_t, i.e. __cxx_atomic_impl<int64_t>,
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// the platform wait is directly monitoring the atomic value itself.
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// `__poll_` takes the current value of the atomic as an in-out argument
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// to potentially modify it. After it returns, `__monitor` has a value
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// which can be safely waited on by `std::__libcpp_atomic_wait` without any
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// ABA style issues.
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__monitor = std::__cxx_atomic_load(__a_, __order_);
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return __poll_(__monitor);
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__monitor_val = __waitable_traits::__atomic_load(__a_, __order_);
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return __poll_(__monitor_val);
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}
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_LIBCPP_AVAILABILITY_SYNC
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_LIBCPP_HIDE_FROM_ABI bool __poll_or_get_monitor(void const volatile*, __cxx_contention_t& __monitor) const {
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// In case we must wait on an atomic from the pool, the monitor comes from
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// `std::__libcpp_atomic_monitor`.
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// Only then we may read from `__a_`. This is the "event count" pattern.
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__monitor = std::__libcpp_atomic_monitor(__a_);
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auto __current_val = std::__cxx_atomic_load(__a_, __order_);
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_LIBCPP_HIDE_FROM_ABI bool
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__update_monitor_val_and_poll(void const volatile* __contention_address, __cxx_contention_t& __monitor_val) const {
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// In case the contention type is anything else, platform wait is monitoring a __cxx_atomic_contention_t
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// from the global pool, the monitor comes from __libcpp_atomic_monitor
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__monitor_val = std::__libcpp_atomic_monitor(__contention_address);
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auto __current_val = __waitable_traits::__atomic_load(__a_, __order_);
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return __poll_(__current_val);
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}
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_LIBCPP_AVAILABILITY_SYNC
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_LIBCPP_HIDE_FROM_ABI bool operator()(chrono::nanoseconds __elapsed) const {
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if (__elapsed > chrono::microseconds(64)) {
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__cxx_contention_t __monitor;
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if (__poll_or_get_monitor(__a_, __monitor))
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auto __contention_address = __waitable_traits::__atomic_contention_address(__a_);
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__cxx_contention_t __monitor_val;
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if (__update_monitor_val_and_poll(__contention_address, __monitor_val))
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return true;
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std::__libcpp_atomic_wait(__a_, __monitor);
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std::__libcpp_atomic_wait(__contention_address, __monitor_val);
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} else if (__elapsed > chrono::microseconds(4))
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__libcpp_thread_yield();
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else {
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@ -105,29 +137,44 @@ struct __libcpp_atomic_wait_backoff_impl {
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// predicate (is the loaded value unequal to `old`?), the predicate function is
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// specified as an argument. The loaded value is given as an in-out argument to
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// the predicate. If the predicate function returns `true`,
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// `_cxx_atomic_wait_unless` will return. If the predicate function returns
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// `__atomic_wait_unless` will return. If the predicate function returns
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// `false`, it must set the argument to its current understanding of the atomic
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// value. The predicate function must not return `false` spuriously.
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template <class _Atp, class _Poll>
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template <class _AtomicWaitable, class _Poll>
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_LIBCPP_AVAILABILITY_SYNC _LIBCPP_HIDE_FROM_ABI void
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__cxx_atomic_wait_unless(_Atp* __a, _Poll&& __poll, memory_order __order) {
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__libcpp_atomic_wait_poll_impl<_Atp, __decay_t<_Poll> > __poll_fn = {__a, __poll, __order};
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__libcpp_atomic_wait_backoff_impl<_Atp, __decay_t<_Poll> > __backoff_fn = {__a, __poll, __order};
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(void)std::__libcpp_thread_poll_with_backoff(__poll_fn, __backoff_fn);
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__atomic_wait_unless(const _AtomicWaitable& __a, _Poll&& __poll, memory_order __order) {
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static_assert(__atomic_waitable<_AtomicWaitable>::value, "");
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__atomic_wait_poll_impl<_AtomicWaitable, __decay_t<_Poll> > __poll_impl = {__a, __poll, __order};
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__atomic_wait_backoff_impl<_AtomicWaitable, __decay_t<_Poll> > __backoff_fn = {__a, __poll, __order};
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std::__libcpp_thread_poll_with_backoff(__poll_impl, __backoff_fn);
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}
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template <class _AtomicWaitable>
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_LIBCPP_AVAILABILITY_SYNC _LIBCPP_HIDE_FROM_ABI void __atomic_notify_one(const _AtomicWaitable& __a) {
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static_assert(__atomic_waitable<_AtomicWaitable>::value, "");
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std::__cxx_atomic_notify_one(__atomic_waitable_traits<__decay_t<_AtomicWaitable> >::__atomic_contention_address(__a));
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}
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template <class _AtomicWaitable>
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_LIBCPP_AVAILABILITY_SYNC _LIBCPP_HIDE_FROM_ABI void __atomic_notify_all(const _AtomicWaitable& __a) {
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static_assert(__atomic_waitable<_AtomicWaitable>::value, "");
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std::__cxx_atomic_notify_all(__atomic_waitable_traits<__decay_t<_AtomicWaitable> >::__atomic_contention_address(__a));
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}
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#else // _LIBCPP_HAS_NO_THREADS
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template <class _Tp>
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_LIBCPP_HIDE_FROM_ABI void __cxx_atomic_notify_all(__cxx_atomic_impl<_Tp> const volatile*) {}
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template <class _Tp>
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_LIBCPP_HIDE_FROM_ABI void __cxx_atomic_notify_one(__cxx_atomic_impl<_Tp> const volatile*) {}
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template <class _Atp, class _Poll>
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_LIBCPP_HIDE_FROM_ABI void __cxx_atomic_wait_unless(_Atp* __a, _Poll&& __poll, memory_order __order) {
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__libcpp_atomic_wait_poll_impl<_Atp, __decay_t<_Poll> > __poll_fn = {__a, __poll, __order};
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(void)std::__libcpp_thread_poll_with_backoff(__poll_fn, __spinning_backoff_policy());
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template <class _AtomicWaitable, class _Poll>
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_LIBCPP_HIDE_FROM_ABI void __atomic_wait_unless(const _AtomicWaitable& __a, _Poll&& __poll, memory_order __order) {
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__atomic_wait_poll_impl<_AtomicWaitable, __decay_t<_Poll> > __poll_fn = {__a, __poll, __order};
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std::__libcpp_thread_poll_with_backoff(__poll_fn, __spinning_backoff_policy());
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}
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template <class _AtomicWaitable>
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_LIBCPP_HIDE_FROM_ABI void __atomic_notify_one(const _AtomicWaitable&) {}
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template <class _AtomicWaitable>
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_LIBCPP_HIDE_FROM_ABI void __atomic_notify_all(const _AtomicWaitable&) {}
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#endif // _LIBCPP_HAS_NO_THREADS
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template <typename _Tp>
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@ -143,11 +190,12 @@ struct __atomic_compare_unequal_to {
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}
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};
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template <class _Atp, class _Tp>
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template <class _AtomicWaitable, class _Up>
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_LIBCPP_AVAILABILITY_SYNC _LIBCPP_HIDE_FROM_ABI void
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__cxx_atomic_wait(_Atp* __a, _Tp const __val, memory_order __order) {
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__atomic_compare_unequal_to<_Tp> __poll_fn = {__val};
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std::__cxx_atomic_wait_unless(__a, __poll_fn, __order);
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__atomic_wait(_AtomicWaitable& __a, _Up __val, memory_order __order) {
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static_assert(__atomic_waitable<_AtomicWaitable>::value, "");
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__atomic_compare_unequal_to<_Up> __nonatomic_equal = {__val};
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std::__atomic_wait_unless(__a, __nonatomic_equal, __order);
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}
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||||
|
||||
_LIBCPP_END_NAMESPACE_STD
|
||||
|
||||
@ -102,8 +102,8 @@ public:
|
||||
return try_wait_impl(__value);
|
||||
}
|
||||
inline _LIBCPP_AVAILABILITY_SYNC _LIBCPP_HIDE_FROM_ABI void wait() const {
|
||||
__cxx_atomic_wait_unless(
|
||||
&__a_.__a_, [this](ptrdiff_t& __value) -> bool { return try_wait_impl(__value); }, memory_order_acquire);
|
||||
std::__atomic_wait_unless(
|
||||
__a_, [this](ptrdiff_t& __value) -> bool { return try_wait_impl(__value); }, memory_order_acquire);
|
||||
}
|
||||
inline _LIBCPP_AVAILABILITY_SYNC _LIBCPP_HIDE_FROM_ABI void arrive_and_wait(ptrdiff_t __update = 1) {
|
||||
_LIBCPP_ASSERT_ARGUMENT_WITHIN_DOMAIN(__update >= 0, "latch::arrive_and_wait called with a negative value");
|
||||
@ -114,7 +114,7 @@ public:
|
||||
}
|
||||
|
||||
private:
|
||||
inline _LIBCPP_HIDE_FROM_ABI bool try_wait_impl(ptrdiff_t& __value) const noexcept { return __value == 0; }
|
||||
_LIBCPP_HIDE_FROM_ABI bool try_wait_impl(ptrdiff_t& __value) const noexcept { return __value == 0; }
|
||||
};
|
||||
|
||||
_LIBCPP_END_NAMESPACE_STD
|
||||
|
||||
@ -99,8 +99,8 @@ public:
|
||||
}
|
||||
}
|
||||
_LIBCPP_AVAILABILITY_SYNC _LIBCPP_HIDE_FROM_ABI void acquire() {
|
||||
__cxx_atomic_wait_unless(
|
||||
&__a_.__a_, [this](ptrdiff_t& __old) { return __try_acquire_impl(__old); }, memory_order_relaxed);
|
||||
std::__atomic_wait_unless(
|
||||
__a_, [this](ptrdiff_t& __old) { return __try_acquire_impl(__old); }, memory_order_relaxed);
|
||||
}
|
||||
template <class _Rep, class _Period>
|
||||
_LIBCPP_AVAILABILITY_SYNC _LIBCPP_HIDE_FROM_ABI bool
|
||||
|
||||
Loading…
x
Reference in New Issue
Block a user