memory.cpp revision 360784
1//===------------------------ memory.cpp ----------------------------------===// 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#include "memory" 10#ifndef _LIBCPP_HAS_NO_THREADS 11#include "mutex" 12#include "thread" 13#if defined(__ELF__) && defined(_LIBCPP_LINK_PTHREAD_LIB) 14#pragma comment(lib, "pthread") 15#endif 16#endif 17#include "include/atomic_support.h" 18 19_LIBCPP_BEGIN_NAMESPACE_STD 20 21const allocator_arg_t allocator_arg = allocator_arg_t(); 22 23bad_weak_ptr::~bad_weak_ptr() _NOEXCEPT {} 24 25const char* 26bad_weak_ptr::what() const _NOEXCEPT 27{ 28 return "bad_weak_ptr"; 29} 30 31__shared_count::~__shared_count() 32{ 33} 34 35__shared_weak_count::~__shared_weak_count() 36{ 37} 38 39#if defined(_LIBCPP_DEPRECATED_ABI_LEGACY_LIBRARY_DEFINITIONS_FOR_INLINE_FUNCTIONS) 40void 41__shared_count::__add_shared() _NOEXCEPT 42{ 43 __libcpp_atomic_refcount_increment(__shared_owners_); 44} 45 46bool 47__shared_count::__release_shared() _NOEXCEPT 48{ 49 if (__libcpp_atomic_refcount_decrement(__shared_owners_) == -1) 50 { 51 __on_zero_shared(); 52 return true; 53 } 54 return false; 55} 56 57void 58__shared_weak_count::__add_shared() _NOEXCEPT 59{ 60 __shared_count::__add_shared(); 61} 62 63void 64__shared_weak_count::__add_weak() _NOEXCEPT 65{ 66 __libcpp_atomic_refcount_increment(__shared_weak_owners_); 67} 68 69void 70__shared_weak_count::__release_shared() _NOEXCEPT 71{ 72 if (__shared_count::__release_shared()) 73 __release_weak(); 74} 75 76#endif // _LIBCPP_DEPRECATED_ABI_LEGACY_LIBRARY_DEFINITIONS_FOR_INLINE_FUNCTIONS 77 78void 79__shared_weak_count::__release_weak() _NOEXCEPT 80{ 81 // NOTE: The acquire load here is an optimization of the very 82 // common case where a shared pointer is being destructed while 83 // having no other contended references. 84 // 85 // BENEFIT: We avoid expensive atomic stores like XADD and STREX 86 // in a common case. Those instructions are slow and do nasty 87 // things to caches. 88 // 89 // IS THIS SAFE? Yes. During weak destruction, if we see that we 90 // are the last reference, we know that no-one else is accessing 91 // us. If someone were accessing us, then they would be doing so 92 // while the last shared / weak_ptr was being destructed, and 93 // that's undefined anyway. 94 // 95 // If we see anything other than a 0, then we have possible 96 // contention, and need to use an atomicrmw primitive. 97 // The same arguments don't apply for increment, where it is legal 98 // (though inadvisable) to share shared_ptr references between 99 // threads, and have them all get copied at once. The argument 100 // also doesn't apply for __release_shared, because an outstanding 101 // weak_ptr::lock() could read / modify the shared count. 102 if (__libcpp_atomic_load(&__shared_weak_owners_, _AO_Acquire) == 0) 103 { 104 // no need to do this store, because we are about 105 // to destroy everything. 106 //__libcpp_atomic_store(&__shared_weak_owners_, -1, _AO_Release); 107 __on_zero_shared_weak(); 108 } 109 else if (__libcpp_atomic_refcount_decrement(__shared_weak_owners_) == -1) 110 __on_zero_shared_weak(); 111} 112 113__shared_weak_count* 114__shared_weak_count::lock() _NOEXCEPT 115{ 116 long object_owners = __libcpp_atomic_load(&__shared_owners_); 117 while (object_owners != -1) 118 { 119 if (__libcpp_atomic_compare_exchange(&__shared_owners_, 120 &object_owners, 121 object_owners+1)) 122 return this; 123 } 124 return nullptr; 125} 126 127#if !defined(_LIBCPP_NO_RTTI) || !defined(_LIBCPP_BUILD_STATIC) 128 129const void* 130__shared_weak_count::__get_deleter(const type_info&) const _NOEXCEPT 131{ 132 return nullptr; 133} 134 135#endif // _LIBCPP_NO_RTTI 136 137#if !defined(_LIBCPP_HAS_NO_ATOMIC_HEADER) 138 139_LIBCPP_SAFE_STATIC static const std::size_t __sp_mut_count = 16; 140_LIBCPP_SAFE_STATIC static __libcpp_mutex_t mut_back[__sp_mut_count] = 141{ 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 _LIBCPP_MUTEX_INITIALIZER, _LIBCPP_MUTEX_INITIALIZER, _LIBCPP_MUTEX_INITIALIZER, _LIBCPP_MUTEX_INITIALIZER 146}; 147 148_LIBCPP_CONSTEXPR __sp_mut::__sp_mut(void* p) _NOEXCEPT 149 : __lx(p) 150{ 151} 152 153void 154__sp_mut::lock() _NOEXCEPT 155{ 156 auto m = static_cast<__libcpp_mutex_t*>(__lx); 157 unsigned count = 0; 158 while (!__libcpp_mutex_trylock(m)) 159 { 160 if (++count > 16) 161 { 162 __libcpp_mutex_lock(m); 163 break; 164 } 165 this_thread::yield(); 166 } 167} 168 169void 170__sp_mut::unlock() _NOEXCEPT 171{ 172 __libcpp_mutex_unlock(static_cast<__libcpp_mutex_t*>(__lx)); 173} 174 175__sp_mut& 176__get_sp_mut(const void* p) 177{ 178 static __sp_mut muts[__sp_mut_count] 179 { 180 &mut_back[ 0], &mut_back[ 1], &mut_back[ 2], &mut_back[ 3], 181 &mut_back[ 4], &mut_back[ 5], &mut_back[ 6], &mut_back[ 7], 182 &mut_back[ 8], &mut_back[ 9], &mut_back[10], &mut_back[11], 183 &mut_back[12], &mut_back[13], &mut_back[14], &mut_back[15] 184 }; 185 return muts[hash<const void*>()(p) & (__sp_mut_count-1)]; 186} 187 188#endif // !defined(_LIBCPP_HAS_NO_ATOMIC_HEADER) 189 190void 191declare_reachable(void*) 192{ 193} 194 195void 196declare_no_pointers(char*, size_t) 197{ 198} 199 200void 201undeclare_no_pointers(char*, size_t) 202{ 203} 204 205#if !defined(_LIBCPP_ABI_POINTER_SAFETY_ENUM_TYPE) 206pointer_safety get_pointer_safety() _NOEXCEPT 207{ 208 return pointer_safety::relaxed; 209} 210#endif 211 212void* 213__undeclare_reachable(void* p) 214{ 215 return p; 216} 217 218void* 219align(size_t alignment, size_t size, void*& ptr, size_t& space) 220{ 221 void* r = nullptr; 222 if (size <= space) 223 { 224 char* p1 = static_cast<char*>(ptr); 225 char* p2 = reinterpret_cast<char*>(reinterpret_cast<size_t>(p1 + (alignment - 1)) & -alignment); 226 size_t d = static_cast<size_t>(p2 - p1); 227 if (d <= space - size) 228 { 229 r = p2; 230 ptr = r; 231 space -= d; 232 } 233 } 234 return r; 235} 236 237_LIBCPP_END_NAMESPACE_STD 238