libcxx/include/__memory/shared_count.h

   1 //===----------------------------------------------------------------------===//
   2 //
   3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
   4 // See https://llvm.org/LICENSE.txt for license information.
   5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   6 //
   7 //===----------------------------------------------------------------------===//
   8
   9 #ifndef _LIBCPP___MEMORY_SHARED_COUNT_H
  10 #define _LIBCPP___MEMORY_SHARED_COUNT_H
  11
  12 #include <__config>
  13 #include <typeinfo>
  14
  15 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
  16 #  pragma GCC system_header
  17 #endif
  18
  19 _LIBCPP_BEGIN_NAMESPACE_STD
  20
  21 // NOTE: Relaxed and acq/rel atomics (for increment and decrement respectively)
  22 // should be sufficient for thread safety.
  23 // See https://llvm.org/PR22803
  24 #if (defined(__clang__) && __has_builtin(__atomic_add_fetch) && defined(__ATOMIC_RELAXED) &&                           \
  25      defined(__ATOMIC_ACQ_REL)) ||                                                                                     \
  26     defined(_LIBCPP_COMPILER_GCC)
  27 #  define _LIBCPP_HAS_BUILTIN_ATOMIC_SUPPORT 1
  28 #else
  29 #  define _LIBCPP_HAS_BUILTIN_ATOMIC_SUPPORT 0
  30 #endif
  31
  32 template <class _ValueType>
  33 inline _LIBCPP_HIDE_FROM_ABI _ValueType __libcpp_relaxed_load(_ValueType const* __value) {
  34 #if _LIBCPP_HAS_THREADS && defined(__ATOMIC_RELAXED) &&                                                                \
  35     (__has_builtin(__atomic_load_n) || defined(_LIBCPP_COMPILER_GCC))
  36   return __atomic_load_n(__value, __ATOMIC_RELAXED);
  37 #else
  38   return *__value;
  39 #endif
  40 }
  41
  42 template <class _ValueType>
  43 inline _LIBCPP_HIDE_FROM_ABI _ValueType __libcpp_acquire_load(_ValueType const* __value) {
  44 #if _LIBCPP_HAS_THREADS && defined(__ATOMIC_ACQUIRE) &&                                                                \
  45     (__has_builtin(__atomic_load_n) || defined(_LIBCPP_COMPILER_GCC))
  46   return __atomic_load_n(__value, __ATOMIC_ACQUIRE);
  47 #else
  48   return *__value;
  49 #endif
  50 }
  51
  52 template <class _Tp>
  53 inline _LIBCPP_HIDE_FROM_ABI _Tp __libcpp_atomic_refcount_increment(_Tp& __t) _NOEXCEPT {
  54 #if _LIBCPP_HAS_BUILTIN_ATOMIC_SUPPORT && _LIBCPP_HAS_THREADS
  55   return __atomic_add_fetch(&__t, 1, __ATOMIC_RELAXED);
  56 #else
  57   return __t += 1;
  58 #endif
  59 }
  60
  61 template <class _Tp>
  62 inline _LIBCPP_HIDE_FROM_ABI _Tp __libcpp_atomic_refcount_decrement(_Tp& __t) _NOEXCEPT {
  63 #if _LIBCPP_HAS_BUILTIN_ATOMIC_SUPPORT && _LIBCPP_HAS_THREADS
  64   return __atomic_add_fetch(&__t, -1, __ATOMIC_ACQ_REL);
  65 #else
  66   return __t -= 1;
  67 #endif
  68 }
  69
  70 class _LIBCPP_EXPORTED_FROM_ABI __shared_count {
  71   __shared_count(const __shared_count&);
  72   __shared_count& operator=(const __shared_count&);
  73
  74 protected:
  75   long __shared_owners_;
  76   virtual ~__shared_count();
  77
  78 private:
  79   virtual void __on_zero_shared() _NOEXCEPT = 0;
  80
  81 public:
  82   _LIBCPP_HIDE_FROM_ABI explicit __shared_count(long __refs = 0) _NOEXCEPT : __shared_owners_(__refs) {}
  83
  84 #if defined(_LIBCPP_SHARED_PTR_DEFINE_LEGACY_INLINE_FUNCTIONS)
  85   void __add_shared() noexcept;
  86   bool __release_shared() noexcept;
  87 #else
  88   _LIBCPP_HIDE_FROM_ABI void __add_shared() _NOEXCEPT { __libcpp_atomic_refcount_increment(__shared_owners_); }
  89   _LIBCPP_HIDE_FROM_ABI bool __release_shared() _NOEXCEPT {
  90     if (__libcpp_atomic_refcount_decrement(__shared_owners_) == -1) {
  91       __on_zero_shared();
  92       return true;
  93     }
  94     return false;
  95   }
  96 #endif
  97   _LIBCPP_HIDE_FROM_ABI long use_count() const _NOEXCEPT { return __libcpp_relaxed_load(&__shared_owners_) + 1; }
  98 };
  99
 100 class _LIBCPP_EXPORTED_FROM_ABI __shared_weak_count : private __shared_count {
 101   long __shared_weak_owners_;
 102
 103 public:
 104   _LIBCPP_HIDE_FROM_ABI explicit __shared_weak_count(long __refs = 0) _NOEXCEPT
 105       : __shared_count(__refs),
 106         __shared_weak_owners_(__refs) {}
 107
 108 protected:
 109   ~__shared_weak_count() override;
 110
 111 public:
 112 #if defined(_LIBCPP_SHARED_PTR_DEFINE_LEGACY_INLINE_FUNCTIONS)
 113   void __add_shared() noexcept;
 114   void __add_weak() noexcept;
 115   void __release_shared() noexcept;
 116 #else
 117   _LIBCPP_HIDE_FROM_ABI void __add_shared() _NOEXCEPT { __shared_count::__add_shared(); }
 118   _LIBCPP_HIDE_FROM_ABI void __add_weak() _NOEXCEPT { __libcpp_atomic_refcount_increment(__shared_weak_owners_); }
 119   _LIBCPP_HIDE_FROM_ABI void __release_shared() _NOEXCEPT {
 120     if (__shared_count::__release_shared())
 121       __release_weak();
 122   }
 123 #endif
 124   void __release_weak() _NOEXCEPT;
 125   _LIBCPP_HIDE_FROM_ABI long use_count() const _NOEXCEPT { return __shared_count::use_count(); }
 126   __shared_weak_count* lock() _NOEXCEPT;
 127
 128   virtual const void* __get_deleter(const type_info&) const _NOEXCEPT;
 129
 130 private:
 131   virtual void __on_zero_shared_weak() _NOEXCEPT = 0;
 132 };
 133
 134 _LIBCPP_END_NAMESPACE_STD
 135
 136 #endif // _LIBCPP___MEMORY_SHARED_COUNT_H