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 #define _LIBCPP_BUILDING_MEMORY 11 #include "memory" 12 #ifndef _LIBCPP_HAS_NO_THREADS 13 #include "mutex" 14 #include "thread" 15 #endif 16 #include "include/atomic_support.h" 17 18 _LIBCPP_BEGIN_NAMESPACE_STD 19 20 const allocator_arg_t allocator_arg = allocator_arg_t(); 21 22 bad_weak_ptr::~bad_weak_ptr() _NOEXCEPT {} 23 24 const char* 25 bad_weak_ptr::what() const _NOEXCEPT 26 { 27 return "bad_weak_ptr"; 28 } 29 30 __shared_count::~__shared_count() 31 { 32 } 33 34 __shared_weak_count::~__shared_weak_count() 35 { 36 } 37 38 #if defined(_LIBCPP_DEPRECATED_ABI_LEGACY_LIBRARY_DEFINITIONS_FOR_INLINE_FUNCTIONS) 39 void 40 __shared_count::__add_shared() _NOEXCEPT 41 { 42 __libcpp_atomic_refcount_increment(__shared_owners_); 43 } 44 45 bool 46 __shared_count::__release_shared() _NOEXCEPT 47 { 48 if (__libcpp_atomic_refcount_decrement(__shared_owners_) == -1) 49 { 50 __on_zero_shared(); 51 return true; 52 } 53 return false; 54 } 55 56 void 57 __shared_weak_count::__add_shared() _NOEXCEPT 58 { 59 __shared_count::__add_shared(); 60 } 61 62 void 63 __shared_weak_count::__add_weak() _NOEXCEPT 64 { 65 __libcpp_atomic_refcount_increment(__shared_weak_owners_); 66 } 67 68 void 69 __shared_weak_count::__release_shared() _NOEXCEPT 70 { 71 if (__shared_count::__release_shared()) 72 __release_weak(); 73 } 74 75 #endif // _LIBCPP_DEPRECATED_ABI_LEGACY_LIBRARY_DEFINITIONS_FOR_INLINE_FUNCTIONS 76 77 void 78 __shared_weak_count::__release_weak() _NOEXCEPT 79 { 80 // NOTE: The acquire load here is an optimization of the very 81 // common case where a shared pointer is being destructed while 82 // having no other contended references. 83 // 84 // BENEFIT: We avoid expensive atomic stores like XADD and STREX 85 // in a common case. Those instructions are slow and do nasty 86 // things to caches. 87 // 88 // IS THIS SAFE? Yes. During weak destruction, if we see that we 89 // are the last reference, we know that no-one else is accessing 90 // us. If someone were accessing us, then they would be doing so 91 // while the last shared / weak_ptr was being destructed, and 92 // that's undefined anyway. 93 // 94 // If we see anything other than a 0, then we have possible 95 // contention, and need to use an atomicrmw primitive. 96 // The same arguments don't apply for increment, where it is legal 97 // (though inadvisable) to share shared_ptr references between 98 // threads, and have them all get copied at once. The argument 99 // also doesn't apply for __release_shared, because an outstanding 100 // weak_ptr::lock() could read / modify the shared count. 101 if (__libcpp_atomic_load(&__shared_weak_owners_, _AO_Acquire) == 0) 102 { 103 // no need to do this store, because we are about 104 // to destroy everything. 105 //__libcpp_atomic_store(&__shared_weak_owners_, -1, _AO_Release); 106 __on_zero_shared_weak(); 107 } 108 else if (__libcpp_atomic_refcount_decrement(__shared_weak_owners_) == -1) 109 __on_zero_shared_weak(); 110 } 111 112 __shared_weak_count* 113 __shared_weak_count::lock() _NOEXCEPT 114 { 115 long object_owners = __libcpp_atomic_load(&__shared_owners_); 116 while (object_owners != -1) 117 { 118 if (__libcpp_atomic_compare_exchange(&__shared_owners_, 119 &object_owners, 120 object_owners+1)) 121 return this; 122 } 123 return nullptr; 124 } 125 126 #if !defined(_LIBCPP_NO_RTTI) || !defined(_LIBCPP_BUILD_STATIC) 127 128 const void* 129 __shared_weak_count::__get_deleter(const type_info&) const _NOEXCEPT 130 { 131 return nullptr; 132 } 133 134 #endif // _LIBCPP_NO_RTTI 135 136 #if !defined(_LIBCPP_HAS_NO_ATOMIC_HEADER) 137 138 _LIBCPP_SAFE_STATIC static const std::size_t __sp_mut_count = 16; 139 _LIBCPP_SAFE_STATIC static __libcpp_mutex_t mut_back[__sp_mut_count] = 140 { 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 _LIBCPP_MUTEX_INITIALIZER, _LIBCPP_MUTEX_INITIALIZER, _LIBCPP_MUTEX_INITIALIZER, _LIBCPP_MUTEX_INITIALIZER 145 }; 146 147 _LIBCPP_CONSTEXPR __sp_mut::__sp_mut(void* p) _NOEXCEPT 148 : __lx(p) 149 { 150 } 151 152 void 153 __sp_mut::lock() _NOEXCEPT 154 { 155 auto m = static_cast<__libcpp_mutex_t*>(__lx); 156 unsigned count = 0; 157 while (!__libcpp_mutex_trylock(m)) 158 { 159 if (++count > 16) 160 { 161 __libcpp_mutex_lock(m); 162 break; 163 } 164 this_thread::yield(); 165 } 166 } 167 168 void 169 __sp_mut::unlock() _NOEXCEPT 170 { 171 __libcpp_mutex_unlock(static_cast<__libcpp_mutex_t*>(__lx)); 172 } 173 174 __sp_mut& 175 __get_sp_mut(const void* p) 176 { 177 static __sp_mut muts[__sp_mut_count] 178 { 179 &mut_back[ 0], &mut_back[ 1], &mut_back[ 2], &mut_back[ 3], 180 &mut_back[ 4], &mut_back[ 5], &mut_back[ 6], &mut_back[ 7], 181 &mut_back[ 8], &mut_back[ 9], &mut_back[10], &mut_back[11], 182 &mut_back[12], &mut_back[13], &mut_back[14], &mut_back[15] 183 }; 184 return muts[hash<const void*>()(p) & (__sp_mut_count-1)]; 185 } 186 187 #endif // !defined(_LIBCPP_HAS_NO_ATOMIC_HEADER) 188 189 void 190 declare_reachable(void*) 191 { 192 } 193 194 void 195 declare_no_pointers(char*, size_t) 196 { 197 } 198 199 void 200 undeclare_no_pointers(char*, size_t) 201 { 202 } 203 204 #if !defined(_LIBCPP_ABI_POINTER_SAFETY_ENUM_TYPE) 205 pointer_safety get_pointer_safety() _NOEXCEPT 206 { 207 return pointer_safety::relaxed; 208 } 209 #endif 210 211 void* 212 __undeclare_reachable(void* p) 213 { 214 return p; 215 } 216 217 void* 218 align(size_t alignment, size_t size, void*& ptr, size_t& space) 219 { 220 void* r = nullptr; 221 if (size <= space) 222 { 223 char* p1 = static_cast<char*>(ptr); 224 char* p2 = reinterpret_cast<char*>(reinterpret_cast<size_t>(p1 + (alignment - 1)) & -alignment); 225 size_t d = static_cast<size_t>(p2 - p1); 226 if (d <= space - size) 227 { 228 r = p2; 229 ptr = r; 230 space -= d; 231 } 232 } 233 return r; 234 } 235 236 _LIBCPP_END_NAMESPACE_STD 237
