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- // shared_ptr atomic access -*- C++ -*-
- // Copyright (C) 2014-2022 Free Software Foundation, Inc.
- //
- // This file is part of the GNU ISO C++ Library. This library is free
- // software; you can redistribute it and/or modify it under the
- // terms of the GNU General Public License as published by the
- // Free Software Foundation; either version 3, or (at your option)
- // any later version.
- // This library is distributed in the hope that it will be useful,
- // but WITHOUT ANY WARRANTY; without even the implied warranty of
- // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
- // GNU General Public License for more details.
- // Under Section 7 of GPL version 3, you are granted additional
- // permissions described in the GCC Runtime Library Exception, version
- // 3.1, as published by the Free Software Foundation.
- // You should have received a copy of the GNU General Public License and
- // a copy of the GCC Runtime Library Exception along with this program;
- // see the files COPYING3 and COPYING.RUNTIME respectively. If not, see
- // <http://www.gnu.org/licenses/>.
- /** @file bits/shared_ptr_atomic.h
- * This is an internal header file, included by other library headers.
- * Do not attempt to use it directly. @headername{memory}
- */
- #ifndef _SHARED_PTR_ATOMIC_H
- #define _SHARED_PTR_ATOMIC_H 1
- #include <bits/atomic_base.h>
- namespace std _GLIBCXX_VISIBILITY(default)
- {
- _GLIBCXX_BEGIN_NAMESPACE_VERSION
- /**
- * @addtogroup pointer_abstractions
- * @{
- */
- /// @relates shared_ptr @{
- /// @cond undocumented
- struct _Sp_locker
- {
- _Sp_locker(const _Sp_locker&) = delete;
- _Sp_locker& operator=(const _Sp_locker&) = delete;
- #ifdef __GTHREADS
- explicit
- _Sp_locker(const void*) noexcept;
- _Sp_locker(const void*, const void*) noexcept;
- ~_Sp_locker();
- private:
- unsigned char _M_key1;
- unsigned char _M_key2;
- #else
- explicit _Sp_locker(const void*, const void* = nullptr) { }
- #endif
- };
- /// @endcond
- /**
- * @brief Report whether shared_ptr atomic operations are lock-free.
- * @param __p A non-null pointer to a shared_ptr object.
- * @return True if atomic access to @c *__p is lock-free, false otherwise.
- * @{
- */
- template<typename _Tp, _Lock_policy _Lp>
- inline bool
- atomic_is_lock_free(const __shared_ptr<_Tp, _Lp>* __p)
- {
- #ifdef __GTHREADS
- return __gthread_active_p() == 0;
- #else
- return true;
- #endif
- }
- template<typename _Tp>
- inline bool
- atomic_is_lock_free(const shared_ptr<_Tp>* __p)
- { return std::atomic_is_lock_free<_Tp, __default_lock_policy>(__p); }
- /// @}
- /**
- * @brief Atomic load for shared_ptr objects.
- * @param __p A non-null pointer to a shared_ptr object.
- * @return @c *__p
- *
- * The memory order shall not be @c memory_order_release or
- * @c memory_order_acq_rel.
- * @{
- */
- template<typename _Tp>
- inline shared_ptr<_Tp>
- atomic_load_explicit(const shared_ptr<_Tp>* __p, memory_order)
- {
- _Sp_locker __lock{__p};
- return *__p;
- }
- template<typename _Tp>
- inline shared_ptr<_Tp>
- atomic_load(const shared_ptr<_Tp>* __p)
- { return std::atomic_load_explicit(__p, memory_order_seq_cst); }
- template<typename _Tp, _Lock_policy _Lp>
- inline __shared_ptr<_Tp, _Lp>
- atomic_load_explicit(const __shared_ptr<_Tp, _Lp>* __p, memory_order)
- {
- _Sp_locker __lock{__p};
- return *__p;
- }
- template<typename _Tp, _Lock_policy _Lp>
- inline __shared_ptr<_Tp, _Lp>
- atomic_load(const __shared_ptr<_Tp, _Lp>* __p)
- { return std::atomic_load_explicit(__p, memory_order_seq_cst); }
- /// @}
- /**
- * @brief Atomic store for shared_ptr objects.
- * @param __p A non-null pointer to a shared_ptr object.
- * @param __r The value to store.
- *
- * The memory order shall not be @c memory_order_acquire or
- * @c memory_order_acq_rel.
- * @{
- */
- template<typename _Tp>
- inline void
- atomic_store_explicit(shared_ptr<_Tp>* __p, shared_ptr<_Tp> __r,
- memory_order)
- {
- _Sp_locker __lock{__p};
- __p->swap(__r); // use swap so that **__p not destroyed while lock held
- }
- template<typename _Tp>
- inline void
- atomic_store(shared_ptr<_Tp>* __p, shared_ptr<_Tp> __r)
- { std::atomic_store_explicit(__p, std::move(__r), memory_order_seq_cst); }
- template<typename _Tp, _Lock_policy _Lp>
- inline void
- atomic_store_explicit(__shared_ptr<_Tp, _Lp>* __p,
- __shared_ptr<_Tp, _Lp> __r,
- memory_order)
- {
- _Sp_locker __lock{__p};
- __p->swap(__r); // use swap so that **__p not destroyed while lock held
- }
- template<typename _Tp, _Lock_policy _Lp>
- inline void
- atomic_store(__shared_ptr<_Tp, _Lp>* __p, __shared_ptr<_Tp, _Lp> __r)
- { std::atomic_store_explicit(__p, std::move(__r), memory_order_seq_cst); }
- /// @}
- /**
- * @brief Atomic exchange for shared_ptr objects.
- * @param __p A non-null pointer to a shared_ptr object.
- * @param __r New value to store in @c *__p.
- * @return The original value of @c *__p
- * @{
- */
- template<typename _Tp>
- inline shared_ptr<_Tp>
- atomic_exchange_explicit(shared_ptr<_Tp>* __p, shared_ptr<_Tp> __r,
- memory_order)
- {
- _Sp_locker __lock{__p};
- __p->swap(__r);
- return __r;
- }
- template<typename _Tp>
- inline shared_ptr<_Tp>
- atomic_exchange(shared_ptr<_Tp>* __p, shared_ptr<_Tp> __r)
- {
- return std::atomic_exchange_explicit(__p, std::move(__r),
- memory_order_seq_cst);
- }
- template<typename _Tp, _Lock_policy _Lp>
- inline __shared_ptr<_Tp, _Lp>
- atomic_exchange_explicit(__shared_ptr<_Tp, _Lp>* __p,
- __shared_ptr<_Tp, _Lp> __r,
- memory_order)
- {
- _Sp_locker __lock{__p};
- __p->swap(__r);
- return __r;
- }
- template<typename _Tp, _Lock_policy _Lp>
- inline __shared_ptr<_Tp, _Lp>
- atomic_exchange(__shared_ptr<_Tp, _Lp>* __p, __shared_ptr<_Tp, _Lp> __r)
- {
- return std::atomic_exchange_explicit(__p, std::move(__r),
- memory_order_seq_cst);
- }
- /// @}
- /**
- * @brief Atomic compare-and-swap for shared_ptr objects.
- * @param __p A non-null pointer to a shared_ptr object.
- * @param __v A non-null pointer to a shared_ptr object.
- * @param __w A non-null pointer to a shared_ptr object.
- * @return True if @c *__p was equivalent to @c *__v, false otherwise.
- *
- * The memory order for failure shall not be @c memory_order_release or
- * @c memory_order_acq_rel, or stronger than the memory order for success.
- * @{
- */
- template<typename _Tp>
- bool
- atomic_compare_exchange_strong_explicit(shared_ptr<_Tp>* __p,
- shared_ptr<_Tp>* __v,
- shared_ptr<_Tp> __w,
- memory_order,
- memory_order)
- {
- shared_ptr<_Tp> __x; // goes out of scope after __lock
- _Sp_locker __lock{__p, __v};
- owner_less<shared_ptr<_Tp>> __less;
- if (*__p == *__v && !__less(*__p, *__v) && !__less(*__v, *__p))
- {
- __x = std::move(*__p);
- *__p = std::move(__w);
- return true;
- }
- __x = std::move(*__v);
- *__v = *__p;
- return false;
- }
- template<typename _Tp>
- inline bool
- atomic_compare_exchange_strong(shared_ptr<_Tp>* __p, shared_ptr<_Tp>* __v,
- shared_ptr<_Tp> __w)
- {
- return std::atomic_compare_exchange_strong_explicit(__p, __v,
- std::move(__w), memory_order_seq_cst, memory_order_seq_cst);
- }
- template<typename _Tp>
- inline bool
- atomic_compare_exchange_weak_explicit(shared_ptr<_Tp>* __p,
- shared_ptr<_Tp>* __v,
- shared_ptr<_Tp> __w,
- memory_order __success,
- memory_order __failure)
- {
- return std::atomic_compare_exchange_strong_explicit(__p, __v,
- std::move(__w), __success, __failure);
- }
- template<typename _Tp>
- inline bool
- atomic_compare_exchange_weak(shared_ptr<_Tp>* __p, shared_ptr<_Tp>* __v,
- shared_ptr<_Tp> __w)
- {
- return std::atomic_compare_exchange_weak_explicit(__p, __v,
- std::move(__w), memory_order_seq_cst, memory_order_seq_cst);
- }
- template<typename _Tp, _Lock_policy _Lp>
- bool
- atomic_compare_exchange_strong_explicit(__shared_ptr<_Tp, _Lp>* __p,
- __shared_ptr<_Tp, _Lp>* __v,
- __shared_ptr<_Tp, _Lp> __w,
- memory_order,
- memory_order)
- {
- __shared_ptr<_Tp, _Lp> __x; // goes out of scope after __lock
- _Sp_locker __lock{__p, __v};
- owner_less<__shared_ptr<_Tp, _Lp>> __less;
- if (*__p == *__v && !__less(*__p, *__v) && !__less(*__v, *__p))
- {
- __x = std::move(*__p);
- *__p = std::move(__w);
- return true;
- }
- __x = std::move(*__v);
- *__v = *__p;
- return false;
- }
- template<typename _Tp, _Lock_policy _Lp>
- inline bool
- atomic_compare_exchange_strong(__shared_ptr<_Tp, _Lp>* __p,
- __shared_ptr<_Tp, _Lp>* __v,
- __shared_ptr<_Tp, _Lp> __w)
- {
- return std::atomic_compare_exchange_strong_explicit(__p, __v,
- std::move(__w), memory_order_seq_cst, memory_order_seq_cst);
- }
- template<typename _Tp, _Lock_policy _Lp>
- inline bool
- atomic_compare_exchange_weak_explicit(__shared_ptr<_Tp, _Lp>* __p,
- __shared_ptr<_Tp, _Lp>* __v,
- __shared_ptr<_Tp, _Lp> __w,
- memory_order __success,
- memory_order __failure)
- {
- return std::atomic_compare_exchange_strong_explicit(__p, __v,
- std::move(__w), __success, __failure);
- }
- template<typename _Tp, _Lock_policy _Lp>
- inline bool
- atomic_compare_exchange_weak(__shared_ptr<_Tp, _Lp>* __p,
- __shared_ptr<_Tp, _Lp>* __v,
- __shared_ptr<_Tp, _Lp> __w)
- {
- return std::atomic_compare_exchange_weak_explicit(__p, __v,
- std::move(__w), memory_order_seq_cst, memory_order_seq_cst);
- }
- /// @}
- #if __cplusplus >= 202002L
- # define __cpp_lib_atomic_shared_ptr 201711L
- template<typename _Tp>
- class atomic;
- template<typename _Up>
- static constexpr bool __is_shared_ptr = false;
- template<typename _Up>
- static constexpr bool __is_shared_ptr<shared_ptr<_Up>> = true;
- template<typename _Tp>
- class _Sp_atomic
- {
- using value_type = _Tp;
- friend class atomic<_Tp>;
- // An atomic version of __shared_count<> and __weak_count<>.
- // Stores a _Sp_counted_base<>* but uses the LSB as a lock.
- struct _Atomic_count
- {
- // Either __shared_count<> or __weak_count<>
- using __count_type = decltype(_Tp::_M_refcount);
- // _Sp_counted_base<>*
- using pointer = decltype(__count_type::_M_pi);
- // Ensure we can use the LSB as the lock bit.
- static_assert(alignof(remove_pointer_t<pointer>) > 1);
- constexpr _Atomic_count() noexcept = default;
- explicit
- _Atomic_count(__count_type&& __c) noexcept
- : _M_val(reinterpret_cast<uintptr_t>(__c._M_pi))
- {
- __c._M_pi = nullptr;
- }
- ~_Atomic_count()
- {
- auto __val = _M_val.load(memory_order_relaxed);
- __glibcxx_assert(!(__val & _S_lock_bit));
- if (auto __pi = reinterpret_cast<pointer>(__val))
- {
- if constexpr (__is_shared_ptr<_Tp>)
- __pi->_M_release();
- else
- __pi->_M_weak_release();
- }
- }
- _Atomic_count(const _Atomic_count&) = delete;
- _Atomic_count& operator=(const _Atomic_count&) = delete;
- // Precondition: Caller does not hold lock!
- // Returns the raw pointer value without the lock bit set.
- pointer
- lock(memory_order __o) const noexcept
- {
- // To acquire the lock we flip the LSB from 0 to 1.
- auto __current = _M_val.load(memory_order_relaxed);
- while (__current & _S_lock_bit)
- {
- #if __cpp_lib_atomic_wait
- __detail::__thread_relax();
- #endif
- __current = _M_val.load(memory_order_relaxed);
- }
- while (!_M_val.compare_exchange_strong(__current,
- __current | _S_lock_bit,
- __o,
- memory_order_relaxed))
- {
- #if __cpp_lib_atomic_wait
- __detail::__thread_relax();
- #endif
- __current = __current & ~_S_lock_bit;
- }
- return reinterpret_cast<pointer>(__current);
- }
- // Precondition: caller holds lock!
- void
- unlock(memory_order __o) const noexcept
- {
- _M_val.fetch_sub(1, __o);
- }
- // Swaps the values of *this and __c, and unlocks *this.
- // Precondition: caller holds lock!
- void
- _M_swap_unlock(__count_type& __c, memory_order __o) noexcept
- {
- if (__o != memory_order_seq_cst)
- __o = memory_order_release;
- auto __x = reinterpret_cast<uintptr_t>(__c._M_pi);
- __x = _M_val.exchange(__x, __o);
- __c._M_pi = reinterpret_cast<pointer>(__x & ~_S_lock_bit);
- }
- #if __cpp_lib_atomic_wait
- // Precondition: caller holds lock!
- void
- _M_wait_unlock(memory_order __o) const noexcept
- {
- auto __v = _M_val.fetch_sub(1, memory_order_relaxed);
- _M_val.wait(__v & ~_S_lock_bit, __o);
- }
- void
- notify_one() noexcept
- {
- _M_val.notify_one();
- }
- void
- notify_all() noexcept
- {
- _M_val.notify_all();
- }
- #endif
- private:
- mutable __atomic_base<uintptr_t> _M_val{0};
- static constexpr uintptr_t _S_lock_bit{1};
- };
- typename _Tp::element_type* _M_ptr = nullptr;
- _Atomic_count _M_refcount;
- static typename _Atomic_count::pointer
- _S_add_ref(typename _Atomic_count::pointer __p)
- {
- if (__p)
- {
- if constexpr (__is_shared_ptr<_Tp>)
- __p->_M_add_ref_copy();
- else
- __p->_M_weak_add_ref();
- }
- return __p;
- }
- constexpr _Sp_atomic() noexcept = default;
- explicit
- _Sp_atomic(value_type __r) noexcept
- : _M_ptr(__r._M_ptr), _M_refcount(std::move(__r._M_refcount))
- { }
- ~_Sp_atomic() = default;
- _Sp_atomic(const _Sp_atomic&) = delete;
- void operator=(const _Sp_atomic&) = delete;
- value_type
- load(memory_order __o) const noexcept
- {
- __glibcxx_assert(__o != memory_order_release
- && __o != memory_order_acq_rel);
- // Ensure that the correct value of _M_ptr is visible after locking.,
- // by upgrading relaxed or consume to acquire.
- if (__o != memory_order_seq_cst)
- __o = memory_order_acquire;
- value_type __ret;
- auto __pi = _M_refcount.lock(__o);
- __ret._M_ptr = _M_ptr;
- __ret._M_refcount._M_pi = _S_add_ref(__pi);
- _M_refcount.unlock(memory_order_relaxed);
- return __ret;
- }
- void
- swap(value_type& __r, memory_order __o) noexcept
- {
- _M_refcount.lock(memory_order_acquire);
- std::swap(_M_ptr, __r._M_ptr);
- _M_refcount._M_swap_unlock(__r._M_refcount, __o);
- }
- bool
- compare_exchange_strong(value_type& __expected, value_type __desired,
- memory_order __o, memory_order __o2) noexcept
- {
- bool __result = true;
- auto __pi = _M_refcount.lock(memory_order_acquire);
- if (_M_ptr == __expected._M_ptr
- && __pi == __expected._M_refcount._M_pi)
- {
- _M_ptr = __desired._M_ptr;
- _M_refcount._M_swap_unlock(__desired._M_refcount, __o);
- }
- else
- {
- _Tp __sink = std::move(__expected);
- __expected._M_ptr = _M_ptr;
- __expected._M_refcount._M_pi = _S_add_ref(__pi);
- _M_refcount.unlock(__o2);
- __result = false;
- }
- return __result;
- }
- #if __cpp_lib_atomic_wait
- void
- wait(value_type __old, memory_order __o) const noexcept
- {
- auto __pi = _M_refcount.lock(memory_order_acquire);
- if (_M_ptr == __old._M_ptr && __pi == __old._M_refcount._M_pi)
- _M_refcount._M_wait_unlock(__o);
- else
- _M_refcount.unlock(memory_order_relaxed);
- }
- void
- notify_one() noexcept
- {
- _M_refcount.notify_one();
- }
- void
- notify_all() noexcept
- {
- _M_refcount.notify_all();
- }
- #endif
- };
- template<typename _Tp>
- class atomic<shared_ptr<_Tp>>
- {
- public:
- using value_type = shared_ptr<_Tp>;
- static constexpr bool is_always_lock_free = false;
- bool
- is_lock_free() const noexcept
- { return false; }
- constexpr atomic() noexcept = default;
- atomic(shared_ptr<_Tp> __r) noexcept
- : _M_impl(std::move(__r))
- { }
- atomic(const atomic&) = delete;
- void operator=(const atomic&) = delete;
- shared_ptr<_Tp>
- load(memory_order __o = memory_order_seq_cst) const noexcept
- { return _M_impl.load(__o); }
- operator shared_ptr<_Tp>() const noexcept
- { return _M_impl.load(memory_order_seq_cst); }
- void
- store(shared_ptr<_Tp> __desired,
- memory_order __o = memory_order_seq_cst) noexcept
- { _M_impl.swap(__desired, __o); }
- void
- operator=(shared_ptr<_Tp> __desired) noexcept
- { _M_impl.swap(__desired, memory_order_seq_cst); }
- shared_ptr<_Tp>
- exchange(shared_ptr<_Tp> __desired,
- memory_order __o = memory_order_seq_cst) noexcept
- {
- _M_impl.swap(__desired, __o);
- return __desired;
- }
- bool
- compare_exchange_strong(shared_ptr<_Tp>& __expected,
- shared_ptr<_Tp> __desired,
- memory_order __o, memory_order __o2) noexcept
- {
- return _M_impl.compare_exchange_strong(__expected, __desired, __o, __o2);
- }
- bool
- compare_exchange_strong(value_type& __expected, value_type __desired,
- memory_order __o = memory_order_seq_cst) noexcept
- {
- memory_order __o2;
- switch (__o)
- {
- case memory_order_acq_rel:
- __o2 = memory_order_acquire;
- break;
- case memory_order_release:
- __o2 = memory_order_relaxed;
- break;
- default:
- __o2 = __o;
- }
- return compare_exchange_strong(__expected, std::move(__desired),
- __o, __o2);
- }
- bool
- compare_exchange_weak(value_type& __expected, value_type __desired,
- memory_order __o, memory_order __o2) noexcept
- {
- return compare_exchange_strong(__expected, std::move(__desired),
- __o, __o2);
- }
- bool
- compare_exchange_weak(value_type& __expected, value_type __desired,
- memory_order __o = memory_order_seq_cst) noexcept
- {
- return compare_exchange_strong(__expected, std::move(__desired), __o);
- }
- #if __cpp_lib_atomic_wait
- void
- wait(value_type __old,
- memory_order __o = memory_order_seq_cst) const noexcept
- {
- _M_impl.wait(std::move(__old), __o);
- }
- void
- notify_one() noexcept
- {
- _M_impl.notify_one();
- }
- void
- notify_all() noexcept
- {
- _M_impl.notify_all();
- }
- #endif
- private:
- _Sp_atomic<shared_ptr<_Tp>> _M_impl;
- };
- template<typename _Tp>
- class atomic<weak_ptr<_Tp>>
- {
- public:
- using value_type = weak_ptr<_Tp>;
- static constexpr bool is_always_lock_free = false;
- bool
- is_lock_free() const noexcept
- { return false; }
- constexpr atomic() noexcept = default;
- atomic(weak_ptr<_Tp> __r) noexcept
- : _M_impl(move(__r))
- { }
- atomic(const atomic&) = delete;
- void operator=(const atomic&) = delete;
- weak_ptr<_Tp>
- load(memory_order __o = memory_order_seq_cst) const noexcept
- { return _M_impl.load(__o); }
- operator weak_ptr<_Tp>() const noexcept
- { return _M_impl.load(memory_order_seq_cst); }
- void
- store(weak_ptr<_Tp> __desired,
- memory_order __o = memory_order_seq_cst) noexcept
- { _M_impl.swap(__desired, __o); }
- void
- operator=(weak_ptr<_Tp> __desired) noexcept
- { _M_impl.swap(__desired, memory_order_seq_cst); }
- weak_ptr<_Tp>
- exchange(weak_ptr<_Tp> __desired,
- memory_order __o = memory_order_seq_cst) noexcept
- {
- _M_impl.swap(__desired, __o);
- return __desired;
- }
- bool
- compare_exchange_strong(weak_ptr<_Tp>& __expected,
- weak_ptr<_Tp> __desired,
- memory_order __o, memory_order __o2) noexcept
- {
- return _M_impl.compare_exchange_strong(__expected, __desired, __o, __o2);
- }
- bool
- compare_exchange_strong(value_type& __expected, value_type __desired,
- memory_order __o = memory_order_seq_cst) noexcept
- {
- memory_order __o2;
- switch (__o)
- {
- case memory_order_acq_rel:
- __o2 = memory_order_acquire;
- break;
- case memory_order_release:
- __o2 = memory_order_relaxed;
- break;
- default:
- __o2 = __o;
- }
- return compare_exchange_strong(__expected, std::move(__desired),
- __o, __o2);
- }
- bool
- compare_exchange_weak(value_type& __expected, value_type __desired,
- memory_order __o, memory_order __o2) noexcept
- {
- return compare_exchange_strong(__expected, std::move(__desired),
- __o, __o2);
- }
- bool
- compare_exchange_weak(value_type& __expected, value_type __desired,
- memory_order __o = memory_order_seq_cst) noexcept
- {
- return compare_exchange_strong(__expected, std::move(__desired), __o);
- }
- #if __cpp_lib_atomic_wait
- void
- wait(value_type __old,
- memory_order __o = memory_order_seq_cst) const noexcept
- {
- _M_impl.wait(std::move(__old), __o);
- }
- void
- notify_one() noexcept
- {
- _M_impl.notify_one();
- }
- void
- notify_all() noexcept
- {
- _M_impl.notify_all();
- }
- #endif
- private:
- _Sp_atomic<weak_ptr<_Tp>> _M_impl;
- };
- #endif // C++20
- /// @} relates shared_ptr
- /// @} group pointer_abstractions
- _GLIBCXX_END_NAMESPACE_VERSION
- } // namespace
- #endif // _SHARED_PTR_ATOMIC_H
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