[libcxx-commits] [libcxx] [libc++] refactor `cxx_atomic_wait` to make it reusable for atomic_ref (PR #81427)
via libcxx-commits
libcxx-commits at lists.llvm.org
Fri Mar 1 11:56:15 PST 2024
https://github.com/huixie90 updated https://github.com/llvm/llvm-project/pull/81427
>From c3e4d3a567583f4340c281f5c58aedc8e030c104 Mon Sep 17 00:00:00 2001
From: Hui <hui.xie0621 at gmail.com>
Date: Sun, 11 Feb 2024 19:11:28 +0000
Subject: [PATCH] [libc++] refactor `cxx_atomic_wait` to make it reusable for
atomic_ref
---
libcxx/include/__atomic/atomic_base.h | 42 ++++++--
libcxx/include/__atomic/atomic_flag.h | 35 +++++--
libcxx/include/__atomic/atomic_sync.h | 141 ++++++++++++++++----------
libcxx/include/latch | 6 +-
libcxx/include/semaphore | 4 +-
5 files changed, 156 insertions(+), 72 deletions(-)
diff --git a/libcxx/include/__atomic/atomic_base.h b/libcxx/include/__atomic/atomic_base.h
index 3ad3b562c59805..6ca01a7f1bf9b9 100644
--- a/libcxx/include/__atomic/atomic_base.h
+++ b/libcxx/include/__atomic/atomic_base.h
@@ -104,24 +104,20 @@ struct __atomic_base // false
_LIBCPP_AVAILABILITY_SYNC _LIBCPP_HIDE_FROM_ABI void wait(_Tp __v, memory_order __m = memory_order_seq_cst) const
volatile _NOEXCEPT {
- std::__cxx_atomic_wait(std::addressof(__a_), __v, __m);
+ std::__atomic_wait(*this, __v, __m);
}
_LIBCPP_AVAILABILITY_SYNC _LIBCPP_HIDE_FROM_ABI void
wait(_Tp __v, memory_order __m = memory_order_seq_cst) const _NOEXCEPT {
- std::__cxx_atomic_wait(std::addressof(__a_), __v, __m);
+ std::__atomic_wait(*this, __v, __m);
}
_LIBCPP_AVAILABILITY_SYNC _LIBCPP_HIDE_FROM_ABI void notify_one() volatile _NOEXCEPT {
- std::__cxx_atomic_notify_one(std::addressof(__a_));
- }
- _LIBCPP_AVAILABILITY_SYNC _LIBCPP_HIDE_FROM_ABI void notify_one() _NOEXCEPT {
- std::__cxx_atomic_notify_one(std::addressof(__a_));
+ std::__atomic_notify_one(*this);
}
+ _LIBCPP_AVAILABILITY_SYNC _LIBCPP_HIDE_FROM_ABI void notify_one() _NOEXCEPT { std::__atomic_notify_one(*this); }
_LIBCPP_AVAILABILITY_SYNC _LIBCPP_HIDE_FROM_ABI void notify_all() volatile _NOEXCEPT {
- std::__cxx_atomic_notify_all(std::addressof(__a_));
- }
- _LIBCPP_AVAILABILITY_SYNC _LIBCPP_HIDE_FROM_ABI void notify_all() _NOEXCEPT {
- std::__cxx_atomic_notify_all(std::addressof(__a_));
+ std::__atomic_notify_all(*this);
}
+ _LIBCPP_AVAILABILITY_SYNC _LIBCPP_HIDE_FROM_ABI void notify_all() _NOEXCEPT { std::__atomic_notify_all(*this); }
#if _LIBCPP_STD_VER >= 20
_LIBCPP_HIDE_FROM_ABI constexpr __atomic_base() noexcept(is_nothrow_default_constructible_v<_Tp>) : __a_(_Tp()) {}
@@ -200,6 +196,32 @@ struct __atomic_base<_Tp, true> : public __atomic_base<_Tp, false> {
_LIBCPP_HIDE_FROM_ABI _Tp operator^=(_Tp __op) _NOEXCEPT { return fetch_xor(__op) ^ __op; }
};
+// Here we need _IsIntegral because the default template argument is not enough
+// e.g __atomic_base<int> is __atomic_base<int, true>, which inherits from
+// __atomic_base<int, false> and the caller of the wait function is
+// __atomic_base<int, false>. So specializing __atomic_base<_Tp> does not work
+template <class _Tp, bool _IsIntegral>
+struct __atomic_waitable_traits<__atomic_base<_Tp, _IsIntegral> > {
+ static _LIBCPP_HIDE_FROM_ABI _Tp __atomic_load(const __atomic_base<_Tp, _IsIntegral>& __a, memory_order __order) {
+ return __a.load(__order);
+ }
+
+ static _LIBCPP_HIDE_FROM_ABI _Tp
+ __atomic_load(const volatile __atomic_base<_Tp, _IsIntegral>& __this, memory_order __order) {
+ return __this.load(__order);
+ }
+
+ static _LIBCPP_HIDE_FROM_ABI const __cxx_atomic_impl<_Tp>*
+ __atomic_contention_address(const __atomic_base<_Tp, _IsIntegral>& __a) {
+ return std::addressof(__a.__a_);
+ }
+
+ static _LIBCPP_HIDE_FROM_ABI const volatile __cxx_atomic_impl<_Tp>*
+ __atomic_contention_address(const volatile __atomic_base<_Tp, _IsIntegral>& __this) {
+ return std::addressof(__this.__a_);
+ }
+};
+
_LIBCPP_END_NAMESPACE_STD
#endif // _LIBCPP___ATOMIC_ATOMIC_BASE_H
diff --git a/libcxx/include/__atomic/atomic_flag.h b/libcxx/include/__atomic/atomic_flag.h
index 18a864523de06f..084366237c16eb 100644
--- a/libcxx/include/__atomic/atomic_flag.h
+++ b/libcxx/include/__atomic/atomic_flag.h
@@ -16,6 +16,7 @@
#include <__availability>
#include <__chrono/duration.h>
#include <__config>
+#include <__memory/addressof.h>
#include <__thread/support.h>
#include <cstdint>
@@ -50,20 +51,20 @@ struct atomic_flag {
_LIBCPP_AVAILABILITY_SYNC _LIBCPP_HIDE_FROM_ABI void wait(bool __v, memory_order __m = memory_order_seq_cst) const
volatile _NOEXCEPT {
- __cxx_atomic_wait(&__a_, _LIBCPP_ATOMIC_FLAG_TYPE(__v), __m);
+ std::__atomic_wait(*this, _LIBCPP_ATOMIC_FLAG_TYPE(__v), __m);
}
_LIBCPP_AVAILABILITY_SYNC _LIBCPP_HIDE_FROM_ABI void
wait(bool __v, memory_order __m = memory_order_seq_cst) const _NOEXCEPT {
- __cxx_atomic_wait(&__a_, _LIBCPP_ATOMIC_FLAG_TYPE(__v), __m);
+ std::__atomic_wait(*this, _LIBCPP_ATOMIC_FLAG_TYPE(__v), __m);
}
_LIBCPP_AVAILABILITY_SYNC _LIBCPP_HIDE_FROM_ABI void notify_one() volatile _NOEXCEPT {
- __cxx_atomic_notify_one(&__a_);
+ std::__atomic_notify_one(*this);
}
- _LIBCPP_AVAILABILITY_SYNC _LIBCPP_HIDE_FROM_ABI void notify_one() _NOEXCEPT { __cxx_atomic_notify_one(&__a_); }
+ _LIBCPP_AVAILABILITY_SYNC _LIBCPP_HIDE_FROM_ABI void notify_one() _NOEXCEPT { std::__atomic_notify_one(*this); }
_LIBCPP_AVAILABILITY_SYNC _LIBCPP_HIDE_FROM_ABI void notify_all() volatile _NOEXCEPT {
- __cxx_atomic_notify_all(&__a_);
+ std::__atomic_notify_all(*this);
}
- _LIBCPP_AVAILABILITY_SYNC _LIBCPP_HIDE_FROM_ABI void notify_all() _NOEXCEPT { __cxx_atomic_notify_all(&__a_); }
+ _LIBCPP_AVAILABILITY_SYNC _LIBCPP_HIDE_FROM_ABI void notify_all() _NOEXCEPT { std::__atomic_notify_all(*this); }
#if _LIBCPP_STD_VER >= 20
_LIBCPP_HIDE_FROM_ABI constexpr atomic_flag() _NOEXCEPT : __a_(false) {}
@@ -78,6 +79,28 @@ struct atomic_flag {
atomic_flag& operator=(const atomic_flag&) volatile = delete;
};
+template <>
+struct __atomic_waitable_traits<atomic_flag> {
+ static _LIBCPP_HIDE_FROM_ABI _LIBCPP_ATOMIC_FLAG_TYPE __atomic_load(const atomic_flag& __a, memory_order __order) {
+ return std::__cxx_atomic_load(&__a.__a_, __order);
+ }
+
+ static _LIBCPP_HIDE_FROM_ABI _LIBCPP_ATOMIC_FLAG_TYPE
+ __atomic_load(const volatile atomic_flag& __a, memory_order __order) {
+ return std::__cxx_atomic_load(&__a.__a_, __order);
+ }
+
+ static _LIBCPP_HIDE_FROM_ABI const __cxx_atomic_impl<_LIBCPP_ATOMIC_FLAG_TYPE>*
+ __atomic_contention_address(const atomic_flag& __a) {
+ return std::addressof(__a.__a_);
+ }
+
+ static _LIBCPP_HIDE_FROM_ABI const volatile __cxx_atomic_impl<_LIBCPP_ATOMIC_FLAG_TYPE>*
+ __atomic_contention_address(const volatile atomic_flag& __a) {
+ return std::addressof(__a.__a_);
+ }
+};
+
inline _LIBCPP_HIDE_FROM_ABI bool atomic_flag_test(const volatile atomic_flag* __o) _NOEXCEPT { return __o->test(); }
inline _LIBCPP_HIDE_FROM_ABI bool atomic_flag_test(const atomic_flag* __o) _NOEXCEPT { return __o->test(); }
diff --git a/libcxx/include/__atomic/atomic_sync.h b/libcxx/include/__atomic/atomic_sync.h
index 2997bad83344b2..efa99aa4b98417 100644
--- a/libcxx/include/__atomic/atomic_sync.h
+++ b/libcxx/include/__atomic/atomic_sync.h
@@ -18,7 +18,11 @@
#include <__memory/addressof.h>
#include <__thread/poll_with_backoff.h>
#include <__thread/support.h>
+#include <__type_traits/conjunction.h>
#include <__type_traits/decay.h>
+#include <__type_traits/invoke.h>
+#include <__type_traits/void_t.h>
+#include <__utility/declval.h>
#include <cstring>
#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
@@ -27,15 +31,45 @@
_LIBCPP_BEGIN_NAMESPACE_STD
-template <class _Atp, class _Poll>
-struct __libcpp_atomic_wait_poll_impl {
- _Atp* __a_;
+// The customisation points to enable the following functions:
+// - __atomic_wait
+// - __atomic_wait_unless
+// - __atomic_notify_one
+// - __atomic_notify_all
+// Note that std::atomic<T>::wait was back-ported to C++03
+// The below implementations look ugly to support C++03
+template <class _Tp, class = void>
+struct __atomic_waitable_traits {
+ template <class _AtomicWaitable>
+ static void __atomic_load(_AtomicWaitable&&, memory_order) = delete;
+
+ template <class _AtomicWaitable>
+ static void __atomic_contention_address(_AtomicWaitable&&) = delete;
+};
+
+template <class _Tp>
+struct __atomic_waitable_traits<_Tp, __enable_if_t<!__is_same(_Tp, __decay_t<_Tp>)> >
+ : __atomic_waitable_traits<__decay_t<_Tp> > {};
+
+template <class _Tp, class = void>
+struct __atomic_waitable : false_type {};
+
+template <class _Tp>
+struct __atomic_waitable<
+ _Tp,
+ __void_t<decltype(__atomic_waitable_traits<_Tp>::__atomic_load(
+ std::declval<const _Tp&>(), std::declval<memory_order>())),
+ decltype(__atomic_waitable_traits<_Tp>::__atomic_contention_address(std::declval<const _Tp&>()))> >
+ : true_type {};
+
+template <class _AtomicWaitable, class _Poll>
+struct __atomic_wait_poll_impl {
+ const _AtomicWaitable& __a_;
_Poll __poll_;
memory_order __order_;
- _LIBCPP_AVAILABILITY_SYNC
_LIBCPP_HIDE_FROM_ABI bool operator()() const {
- auto __current_val = std::__cxx_atomic_load(__a_, __order_);
+ auto __current_val = __atomic_waitable_traits<_AtomicWaitable>::__atomic_load(__a_, __order_);
return __poll_(__current_val);
}
};
@@ -56,42 +90,39 @@ __libcpp_atomic_monitor(__cxx_atomic_contention_t const volatile*);
_LIBCPP_AVAILABILITY_SYNC _LIBCPP_EXPORTED_FROM_ABI void
__libcpp_atomic_wait(__cxx_atomic_contention_t const volatile*, __cxx_contention_t);
-template <class _Atp, class _Poll>
-struct __libcpp_atomic_wait_backoff_impl {
- _Atp* __a_;
+template <class _AtomicWaitable, class _Poll>
+struct __atomic_wait_backoff_impl {
+ const _AtomicWaitable& __a_;
_Poll __poll_;
memory_order __order_;
_LIBCPP_AVAILABILITY_SYNC
_LIBCPP_HIDE_FROM_ABI bool
- __poll_or_get_monitor(__cxx_atomic_contention_t const volatile*, __cxx_contention_t& __monitor) const {
- // In case the atomic can be waited on directly, the monitor value is just
- // the value of the atomic.
- // `__poll_` takes the current value of the atomic as an in-out argument
- // to potentially modify it. After it returns, `__monitor` has a value
- // which can be safely waited on by `std::__libcpp_atomic_wait` without any
- // ABA style issues.
- __monitor = std::__cxx_atomic_load(__a_, __order_);
- return __poll_(__monitor);
+ __update_monitor_val_and_poll(__cxx_atomic_contention_t const volatile*, __cxx_contention_t& __monitor_val) const {
+ // In case the contention type happens to be __cxx_atomic_contention_t, i.e. __cxx_atomic_impl<int64_t>,
+ // the platform wait is directly monitoring the atomic value itself.
+ __monitor_val = __atomic_waitable_traits<_AtomicWaitable>::__atomic_load(__a_, __order_);
+ return __poll_(__monitor_val);
}
_LIBCPP_AVAILABILITY_SYNC
- _LIBCPP_HIDE_FROM_ABI bool __poll_or_get_monitor(void const volatile*, __cxx_contention_t& __monitor) const {
- // In case we must wait on an atomic from the pool, the monitor comes from
- // `std::__libcpp_atomic_monitor`.
- // Only then we may read from `__a_`. This is the "event count" pattern.
- __monitor = std::__libcpp_atomic_monitor(__a_);
- auto __current_val = std::__cxx_atomic_load(__a_, __order_);
+ _LIBCPP_HIDE_FROM_ABI bool
+ __update_monitor_val_and_poll(void const volatile* __contention_address, __cxx_contention_t& __monitor_val) const {
+ // In case the contention type is anything else, platform wait is monitoring a __cxx_atomic_contention_t
+ // from the global pool, the monitor comes from __libcpp_atomic_monitor
+ __monitor_val = std::__libcpp_atomic_monitor(__contention_address);
+ auto __current_val = __atomic_waitable_traits<_AtomicWaitable>::__atomic_load(__a_, __order_);
return __poll_(__current_val);
}
_LIBCPP_AVAILABILITY_SYNC
_LIBCPP_HIDE_FROM_ABI bool operator()(chrono::nanoseconds __elapsed) const {
if (__elapsed > chrono::microseconds(64)) {
- __cxx_contention_t __monitor;
- if (__poll_or_get_monitor(__a_, __monitor))
+ auto __contention_address = __atomic_waitable_traits<_AtomicWaitable>::__atomic_contention_address(__a_);
+ __cxx_contention_t __monitor_val;
+ if (__update_monitor_val_and_poll(__contention_address, __monitor_val))
return true;
- std::__libcpp_atomic_wait(__a_, __monitor);
+ std::__libcpp_atomic_wait(__contention_address, __monitor_val);
} else if (__elapsed > chrono::microseconds(4))
__libcpp_thread_yield();
else {
@@ -100,34 +131,41 @@ struct __libcpp_atomic_wait_backoff_impl {
}
};
-// The semantics of this function are similar to `atomic`'s
-// `.wait(T old, std::memory_order order)`, but instead of having a hardcoded
-// predicate (is the loaded value unequal to `old`?), the predicate function is
-// specified as an argument. The loaded value is given as an in-out argument to
-// the predicate. If the predicate function returns `true`,
-// `_cxx_atomic_wait_unless` will return. If the predicate function returns
-// `false`, it must set the argument to its current understanding of the atomic
-// value. The predicate function must not return `false` spuriously.
-template <class _Atp, class _Poll>
+template <class _AtomicWaitable, class _Poll>
_LIBCPP_AVAILABILITY_SYNC _LIBCPP_HIDE_FROM_ABI void
-__cxx_atomic_wait_unless(_Atp* __a, _Poll&& __poll, memory_order __order) {
- __libcpp_atomic_wait_poll_impl<_Atp, __decay_t<_Poll> > __poll_fn = {__a, __poll, __order};
- __libcpp_atomic_wait_backoff_impl<_Atp, __decay_t<_Poll> > __backoff_fn = {__a, __poll, __order};
- (void)std::__libcpp_thread_poll_with_backoff(__poll_fn, __backoff_fn);
+__atomic_wait_unless(const _AtomicWaitable& __a, _Poll&& __poll, memory_order __order) {
+ static_assert(__atomic_waitable<_AtomicWaitable>::value, "");
+ __atomic_wait_poll_impl<_AtomicWaitable, __decay_t<_Poll> > __poll_impl = {__a, __poll, __order};
+ __atomic_wait_backoff_impl<_AtomicWaitable, __decay_t<_Poll> > __backoff_fn = {__a, __poll, __order};
+ std::__libcpp_thread_poll_with_backoff(__poll_impl, __backoff_fn);
+}
+
+template <class _AtomicWaitable>
+_LIBCPP_AVAILABILITY_SYNC _LIBCPP_HIDE_FROM_ABI void __atomic_notify_one(const _AtomicWaitable& __a) {
+ static_assert(__atomic_waitable<_AtomicWaitable>::value, "");
+ std::__cxx_atomic_notify_one(__atomic_waitable_traits<_AtomicWaitable>::__atomic_contention_address(__a));
+}
+
+template <class _AtomicWaitable>
+_LIBCPP_AVAILABILITY_SYNC _LIBCPP_HIDE_FROM_ABI void __atomic_notify_all(const _AtomicWaitable& __a) {
+ static_assert(__atomic_waitable<_AtomicWaitable>::value, "");
+ std::__cxx_atomic_notify_all(__atomic_waitable_traits<_AtomicWaitable>::__atomic_contention_address(__a));
}
#else // _LIBCPP_HAS_NO_THREADS
-template <class _Tp>
-_LIBCPP_HIDE_FROM_ABI void __cxx_atomic_notify_all(__cxx_atomic_impl<_Tp> const volatile*) {}
-template <class _Tp>
-_LIBCPP_HIDE_FROM_ABI void __cxx_atomic_notify_one(__cxx_atomic_impl<_Tp> const volatile*) {}
-template <class _Atp, class _Poll>
-_LIBCPP_HIDE_FROM_ABI void __cxx_atomic_wait_unless(_Atp* __a, _Poll&& __poll, memory_order __order) {
- __libcpp_atomic_wait_poll_impl<_Atp, __decay_t<_Poll> > __poll_fn = {__a, __poll, __order};
- (void)std::__libcpp_thread_poll_with_backoff(__poll_fn, __spinning_backoff_policy());
+template <class _AtomicWaitable, class _Poll>
+_LIBCPP_HIDE_FROM_ABI void __atomic_wait_unless(const _AtomicWaitable& __a, _Poll&& __poll, memory_order __order) {
+ __atomic_wait_poll_impl<_AtomicWaitable, __decay_t<_Poll> > __poll_fn = {__a, __poll, __order};
+ std::__libcpp_thread_poll_with_backoff(__poll_fn, __spinning_backoff_policy());
}
+template <class _AtomicWaitable>
+_LIBCPP_HIDE_FROM_ABI void __atomic_notify_one(const _AtomicWaitable&) {}
+
+template <class _AtomicWaitable>
+_LIBCPP_HIDE_FROM_ABI void __atomic_notify_all(const _AtomicWaitable&) {}
+
#endif // _LIBCPP_HAS_NO_THREADS
template <typename _Tp>
@@ -143,11 +181,12 @@ struct __atomic_compare_unequal_to {
}
};
-template <class _Atp, class _Tp>
+template <class _AtomicWaitable, class _Up>
_LIBCPP_AVAILABILITY_SYNC _LIBCPP_HIDE_FROM_ABI void
-__cxx_atomic_wait(_Atp* __a, _Tp const __val, memory_order __order) {
- __atomic_compare_unequal_to<_Tp> __poll_fn = {__val};
- std::__cxx_atomic_wait_unless(__a, __poll_fn, __order);
+__atomic_wait(_AtomicWaitable& __a, _Up __val, memory_order __order) {
+ static_assert(__atomic_waitable<_AtomicWaitable>::value, "");
+ __atomic_compare_unequal_to<_Up> __nonatomic_equal = {__val};
+ std::__atomic_wait_unless(__a, __nonatomic_equal, __order);
}
_LIBCPP_END_NAMESPACE_STD
diff --git a/libcxx/include/latch b/libcxx/include/latch
index 3fe201b63d1385..3cc72583811434 100644
--- a/libcxx/include/latch
+++ b/libcxx/include/latch
@@ -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
diff --git a/libcxx/include/semaphore b/libcxx/include/semaphore
index 2dfdae9aa148c1..1375ec3f7c04b1 100644
--- a/libcxx/include/semaphore
+++ b/libcxx/include/semaphore
@@ -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
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