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
~bad_weak_ptr()21 bad_weak_ptr::~bad_weak_ptr() _NOEXCEPT {}
22
23 const char*
what() const24 bad_weak_ptr::what() const _NOEXCEPT
25 {
26 return "bad_weak_ptr";
27 }
28
~__shared_count()29 __shared_count::~__shared_count()
30 {
31 }
32
~__shared_weak_count()33 __shared_weak_count::~__shared_weak_count()
34 {
35 }
36
37 #if defined(_LIBCPP_DEPRECATED_ABI_LEGACY_LIBRARY_DEFINITIONS_FOR_INLINE_FUNCTIONS)
38 void
__add_shared()39 __shared_count::__add_shared() _NOEXCEPT
40 {
41 __libcpp_atomic_refcount_increment(__shared_owners_);
42 }
43
44 bool
__release_shared()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
__add_shared()56 __shared_weak_count::__add_shared() _NOEXCEPT
57 {
58 __shared_count::__add_shared();
59 }
60
61 void
__add_weak()62 __shared_weak_count::__add_weak() _NOEXCEPT
63 {
64 __libcpp_atomic_refcount_increment(__shared_weak_owners_);
65 }
66
67 void
__release_shared()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
__release_weak()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*
lock()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*
__get_deleter(const type_info &) const128 __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
__sp_mut(void * p)146 _LIBCPP_CONSTEXPR __sp_mut::__sp_mut(void* p) _NOEXCEPT
147 : __lx(p)
148 {
149 }
150
151 void
lock()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
unlock()168 __sp_mut::unlock() _NOEXCEPT
169 {
170 __libcpp_mutex_unlock(static_cast<__libcpp_mutex_t*>(__lx));
171 }
172
173 __sp_mut&
__get_sp_mut(const void * p)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
declare_reachable(void *)189 declare_reachable(void*)
190 {
191 }
192
193 void
declare_no_pointers(char *,size_t)194 declare_no_pointers(char*, size_t)
195 {
196 }
197
198 void
undeclare_no_pointers(char *,size_t)199 undeclare_no_pointers(char*, size_t)
200 {
201 }
202
203 #if !defined(_LIBCPP_ABI_POINTER_SAFETY_ENUM_TYPE)
get_pointer_safety()204 pointer_safety get_pointer_safety() _NOEXCEPT
205 {
206 return pointer_safety::relaxed;
207 }
208 #endif
209
210 void*
__undeclare_reachable(void * p)211 __undeclare_reachable(void* p)
212 {
213 return p;
214 }
215
216 void*
align(size_t alignment,size_t size,void * & ptr,size_t & space)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