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