xref: /freebsd/contrib/llvm-project/libcxx/src/memory.cpp (revision cfd6422a5217410fbd66f7a7a8a64d9d85e61229)
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 
21 const allocator_arg_t allocator_arg = allocator_arg_t();
22 
23 bad_weak_ptr::~bad_weak_ptr() _NOEXCEPT {}
24 
25 const char*
26 bad_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)
40 void
41 __shared_count::__add_shared() _NOEXCEPT
42 {
43     __libcpp_atomic_refcount_increment(__shared_owners_);
44 }
45 
46 bool
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 
57 void
58 __shared_weak_count::__add_shared() _NOEXCEPT
59 {
60     __shared_count::__add_shared();
61 }
62 
63 void
64 __shared_weak_count::__add_weak() _NOEXCEPT
65 {
66     __libcpp_atomic_refcount_increment(__shared_weak_owners_);
67 }
68 
69 void
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 
78 void
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 
129 const 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 
153 void
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 
169 void
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 
190 void
191 declare_reachable(void*)
192 {
193 }
194 
195 void
196 declare_no_pointers(char*, size_t)
197 {
198 }
199 
200 void
201 undeclare_no_pointers(char*, size_t)
202 {
203 }
204 
205 #if !defined(_LIBCPP_ABI_POINTER_SAFETY_ENUM_TYPE)
206 pointer_safety get_pointer_safety() _NOEXCEPT
207 {
208     return pointer_safety::relaxed;
209 }
210 #endif
211 
212 void*
213 __undeclare_reachable(void* p)
214 {
215     return p;
216 }
217 
218 void*
219 align(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