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