1 //===------------------------ memory.cpp ----------------------------------===// 2 // 3 // The LLVM Compiler Infrastructure 4 // 5 // This file is dual licensed under the MIT and the University of Illinois Open 6 // Source Licenses. See LICENSE.TXT for details. 7 // 8 //===----------------------------------------------------------------------===// 9 10 #include "memory" 11 #ifndef _LIBCPP_HAS_NO_THREADS 12 #include "mutex" 13 #include "thread" 14 #endif 15 #include "include/atomic_support.h" 16 17 _LIBCPP_BEGIN_NAMESPACE_STD 18 19 const allocator_arg_t allocator_arg = allocator_arg_t(); 20 21 bad_weak_ptr::~bad_weak_ptr() _NOEXCEPT {} 22 23 const char* 24 bad_weak_ptr::what() const _NOEXCEPT 25 { 26 return "bad_weak_ptr"; 27 } 28 29 __shared_count::~__shared_count() 30 { 31 } 32 33 __shared_weak_count::~__shared_weak_count() 34 { 35 } 36 37 #if defined(_LIBCPP_DEPRECATED_ABI_LEGACY_LIBRARY_DEFINITIONS_FOR_INLINE_FUNCTIONS) 38 void 39 __shared_count::__add_shared() _NOEXCEPT 40 { 41 __libcpp_atomic_refcount_increment(__shared_owners_); 42 } 43 44 bool 45 __shared_count::__release_shared() _NOEXCEPT 46 { 47 if (__libcpp_atomic_refcount_decrement(__shared_owners_) == -1) 48 { 49 __on_zero_shared(); 50 return true; 51 } 52 return false; 53 } 54 55 void 56 __shared_weak_count::__add_shared() _NOEXCEPT 57 { 58 __shared_count::__add_shared(); 59 } 60 61 void 62 __shared_weak_count::__add_weak() _NOEXCEPT 63 { 64 __libcpp_atomic_refcount_increment(__shared_weak_owners_); 65 } 66 67 void 68 __shared_weak_count::__release_shared() _NOEXCEPT 69 { 70 if (__shared_count::__release_shared()) 71 __release_weak(); 72 } 73 74 #endif // _LIBCPP_DEPRECATED_ABI_LEGACY_LIBRARY_DEFINITIONS_FOR_INLINE_FUNCTIONS 75 76 void 77 __shared_weak_count::__release_weak() _NOEXCEPT 78 { 79 // NOTE: The acquire load here is an optimization of the very 80 // common case where a shared pointer is being destructed while 81 // having no other contended references. 82 // 83 // BENEFIT: We avoid expensive atomic stores like XADD and STREX 84 // in a common case. Those instructions are slow and do nasty 85 // things to caches. 86 // 87 // IS THIS SAFE? Yes. During weak destruction, if we see that we 88 // are the last reference, we know that no-one else is accessing 89 // us. If someone were accessing us, then they would be doing so 90 // while the last shared / weak_ptr was being destructed, and 91 // that's undefined anyway. 92 // 93 // If we see anything other than a 0, then we have possible 94 // contention, and need to use an atomicrmw primitive. 95 // The same arguments don't apply for increment, where it is legal 96 // (though inadvisable) to share shared_ptr references between 97 // threads, and have them all get copied at once. The argument 98 // also doesn't apply for __release_shared, because an outstanding 99 // weak_ptr::lock() could read / modify the shared count. 100 if (__libcpp_atomic_load(&__shared_weak_owners_, _AO_Acquire) == 0) 101 { 102 // no need to do this store, because we are about 103 // to destroy everything. 104 //__libcpp_atomic_store(&__shared_weak_owners_, -1, _AO_Release); 105 __on_zero_shared_weak(); 106 } 107 else if (__libcpp_atomic_refcount_decrement(__shared_weak_owners_) == -1) 108 __on_zero_shared_weak(); 109 } 110 111 __shared_weak_count* 112 __shared_weak_count::lock() _NOEXCEPT 113 { 114 long object_owners = __libcpp_atomic_load(&__shared_owners_); 115 while (object_owners != -1) 116 { 117 if (__libcpp_atomic_compare_exchange(&__shared_owners_, 118 &object_owners, 119 object_owners+1)) 120 return this; 121 } 122 return nullptr; 123 } 124 125 #if !defined(_LIBCPP_NO_RTTI) || !defined(_LIBCPP_BUILD_STATIC) 126 127 const void* 128 __shared_weak_count::__get_deleter(const type_info&) const _NOEXCEPT 129 { 130 return nullptr; 131 } 132 133 #endif // _LIBCPP_NO_RTTI 134 135 #if !defined(_LIBCPP_HAS_NO_ATOMIC_HEADER) 136 137 _LIBCPP_SAFE_STATIC static const std::size_t __sp_mut_count = 16; 138 _LIBCPP_SAFE_STATIC static __libcpp_mutex_t mut_back[__sp_mut_count] = 139 { 140 _LIBCPP_MUTEX_INITIALIZER, _LIBCPP_MUTEX_INITIALIZER, _LIBCPP_MUTEX_INITIALIZER, _LIBCPP_MUTEX_INITIALIZER, 141 _LIBCPP_MUTEX_INITIALIZER, _LIBCPP_MUTEX_INITIALIZER, _LIBCPP_MUTEX_INITIALIZER, _LIBCPP_MUTEX_INITIALIZER, 142 _LIBCPP_MUTEX_INITIALIZER, _LIBCPP_MUTEX_INITIALIZER, _LIBCPP_MUTEX_INITIALIZER, _LIBCPP_MUTEX_INITIALIZER, 143 _LIBCPP_MUTEX_INITIALIZER, _LIBCPP_MUTEX_INITIALIZER, _LIBCPP_MUTEX_INITIALIZER, _LIBCPP_MUTEX_INITIALIZER 144 }; 145 146 _LIBCPP_CONSTEXPR __sp_mut::__sp_mut(void* p) _NOEXCEPT 147 : __lx(p) 148 { 149 } 150 151 void 152 __sp_mut::lock() _NOEXCEPT 153 { 154 auto m = static_cast<__libcpp_mutex_t*>(__lx); 155 unsigned count = 0; 156 while (!__libcpp_mutex_trylock(m)) 157 { 158 if (++count > 16) 159 { 160 __libcpp_mutex_lock(m); 161 break; 162 } 163 this_thread::yield(); 164 } 165 } 166 167 void 168 __sp_mut::unlock() _NOEXCEPT 169 { 170 __libcpp_mutex_unlock(static_cast<__libcpp_mutex_t*>(__lx)); 171 } 172 173 __sp_mut& 174 __get_sp_mut(const void* p) 175 { 176 static __sp_mut muts[__sp_mut_count] 177 { 178 &mut_back[ 0], &mut_back[ 1], &mut_back[ 2], &mut_back[ 3], 179 &mut_back[ 4], &mut_back[ 5], &mut_back[ 6], &mut_back[ 7], 180 &mut_back[ 8], &mut_back[ 9], &mut_back[10], &mut_back[11], 181 &mut_back[12], &mut_back[13], &mut_back[14], &mut_back[15] 182 }; 183 return muts[hash<const void*>()(p) & (__sp_mut_count-1)]; 184 } 185 186 #endif // !defined(_LIBCPP_HAS_NO_ATOMIC_HEADER) 187 188 void 189 declare_reachable(void*) 190 { 191 } 192 193 void 194 declare_no_pointers(char*, size_t) 195 { 196 } 197 198 void 199 undeclare_no_pointers(char*, size_t) 200 { 201 } 202 203 #if !defined(_LIBCPP_ABI_POINTER_SAFETY_ENUM_TYPE) 204 pointer_safety get_pointer_safety() _NOEXCEPT 205 { 206 return pointer_safety::relaxed; 207 } 208 #endif 209 210 void* 211 __undeclare_reachable(void* p) 212 { 213 return p; 214 } 215 216 void* 217 align(size_t alignment, size_t size, void*& ptr, size_t& space) 218 { 219 void* r = nullptr; 220 if (size <= space) 221 { 222 char* p1 = static_cast<char*>(ptr); 223 char* p2 = reinterpret_cast<char*>(reinterpret_cast<size_t>(p1 + (alignment - 1)) & -alignment); 224 size_t d = static_cast<size_t>(p2 - p1); 225 if (d <= space - size) 226 { 227 r = p2; 228 ptr = r; 229 space -= d; 230 } 231 } 232 return r; 233 } 234 235 _LIBCPP_END_NAMESPACE_STD 236
