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
28bad_weak_ptr::~bad_weak_ptr() noexcept {}
29
30const char* bad_weak_ptr::what() const noexcept { return "bad_weak_ptr"; }
31
32__shared_count::~__shared_count() {}
33
34__shared_weak_count::~__shared_weak_count() {}
35
36#if defined(_LIBCPP_SHARED_PTR_DEFINE_LEGACY_INLINE_FUNCTIONS)
37void __shared_count::__add_shared() noexcept { __libcpp_atomic_refcount_increment(__shared_owners_); }
38
39bool __shared_count::__release_shared() noexcept {
40 if (__libcpp_atomic_refcount_decrement(__shared_owners_) == -1) {
41 __on_zero_shared();
42 return true;
43 }
44 return false;
45}
46
47void __shared_weak_count::__add_shared() noexcept { __shared_count::__add_shared(); }
48
49void __shared_weak_count::__add_weak() noexcept { __libcpp_atomic_refcount_increment(__shared_weak_owners_); }
50
51void __shared_weak_count::__release_shared() noexcept {
52 if (__shared_count::__release_shared())
53 __release_weak();
54}
55#endif // _LIBCPP_SHARED_PTR_DEFINE_LEGACY_INLINE_FUNCTIONS
56
57void __shared_weak_count::__release_weak() noexcept {
58 // NOTE: The acquire load here is an optimization of the very
59 // common case where a shared pointer is being destructed while
60 // having no other contended references.
61 //
62 // BENEFIT: We avoid expensive atomic stores like XADD and STREX
63 // in a common case. Those instructions are slow and do nasty
64 // things to caches.
65 //
66 // IS THIS SAFE? Yes. During weak destruction, if we see that we
67 // are the last reference, we know that no-one else is accessing
68 // us. If someone were accessing us, then they would be doing so
69 // while the last shared / weak_ptr was being destructed, and
70 // that's undefined anyway.
71 //
72 // If we see anything other than a 0, then we have possible
73 // contention, and need to use an atomicrmw primitive.
74 // The same arguments don't apply for increment, where it is legal
75 // (though inadvisable) to share shared_ptr references between
76 // threads, and have them all get copied at once. The argument
77 // also doesn't apply for __release_shared, because an outstanding
78 // weak_ptr::lock() could read / modify the shared count.
79 if (__libcpp_atomic_load(&__shared_weak_owners_, _AO_Acquire) == 0) {
80 // no need to do this store, because we are about
81 // to destroy everything.
82 //__libcpp_atomic_store(&__shared_weak_owners_, -1, _AO_Release);
83 __on_zero_shared_weak();
84 } else if (__libcpp_atomic_refcount_decrement(__shared_weak_owners_) == -1)
85 __on_zero_shared_weak();
86}
87
88__shared_weak_count* __shared_weak_count::lock() noexcept {
89 long object_owners = __libcpp_atomic_load(&__shared_owners_);
90 while (object_owners != -1) {
91 if (__libcpp_atomic_compare_exchange(&__shared_owners_, &object_owners, object_owners + 1))
92 return this;
93 }
94 return nullptr;
95}
96
97const void* __shared_weak_count::__get_deleter(const type_info&) const noexcept { return nullptr; }
98
99#if !defined(_LIBCPP_HAS_NO_THREADS)
100
101static constexpr std::size_t __sp_mut_count = 32;
102static constinit __libcpp_mutex_t mut_back[__sp_mut_count] = {
103 _LIBCPP_MUTEX_INITIALIZER, _LIBCPP_MUTEX_INITIALIZER, _LIBCPP_MUTEX_INITIALIZER, _LIBCPP_MUTEX_INITIALIZER,
104 _LIBCPP_MUTEX_INITIALIZER, _LIBCPP_MUTEX_INITIALIZER, _LIBCPP_MUTEX_INITIALIZER, _LIBCPP_MUTEX_INITIALIZER,
105 _LIBCPP_MUTEX_INITIALIZER, _LIBCPP_MUTEX_INITIALIZER, _LIBCPP_MUTEX_INITIALIZER, _LIBCPP_MUTEX_INITIALIZER,
106 _LIBCPP_MUTEX_INITIALIZER, _LIBCPP_MUTEX_INITIALIZER, _LIBCPP_MUTEX_INITIALIZER, _LIBCPP_MUTEX_INITIALIZER,
107 _LIBCPP_MUTEX_INITIALIZER, _LIBCPP_MUTEX_INITIALIZER, _LIBCPP_MUTEX_INITIALIZER, _LIBCPP_MUTEX_INITIALIZER,
108 _LIBCPP_MUTEX_INITIALIZER, _LIBCPP_MUTEX_INITIALIZER, _LIBCPP_MUTEX_INITIALIZER, _LIBCPP_MUTEX_INITIALIZER,
109 _LIBCPP_MUTEX_INITIALIZER, _LIBCPP_MUTEX_INITIALIZER, _LIBCPP_MUTEX_INITIALIZER, _LIBCPP_MUTEX_INITIALIZER,
110 _LIBCPP_MUTEX_INITIALIZER, _LIBCPP_MUTEX_INITIALIZER, _LIBCPP_MUTEX_INITIALIZER, _LIBCPP_MUTEX_INITIALIZER};
111
112constexpr __sp_mut::__sp_mut(void* p) noexcept : __lx_(p) {}
113
114void __sp_mut::lock() noexcept {
115 auto m = static_cast<__libcpp_mutex_t*>(__lx_);
116 __libcpp_mutex_lock(m);
117}
118
119void __sp_mut::unlock() noexcept { __libcpp_mutex_unlock(static_cast<__libcpp_mutex_t*>(__lx_)); }
120
121__sp_mut& __get_sp_mut(const void* p) {
122 static constinit __sp_mut muts[__sp_mut_count] = {
123 &mut_back[0], &mut_back[1], &mut_back[2], &mut_back[3], &mut_back[4], &mut_back[5], &mut_back[6],
124 &mut_back[7], &mut_back[8], &mut_back[9], &mut_back[10], &mut_back[11], &mut_back[12], &mut_back[13],
125 &mut_back[14], &mut_back[15], &mut_back[16], &mut_back[17], &mut_back[18], &mut_back[19], &mut_back[20],
126 &mut_back[21], &mut_back[22], &mut_back[23], &mut_back[24], &mut_back[25], &mut_back[26], &mut_back[27],
127 &mut_back[28], &mut_back[29], &mut_back[30], &mut_back[31]};
128 return muts[hash<const void*>()(p) & (__sp_mut_count - 1)];
129}
130
131#endif // !defined(_LIBCPP_HAS_NO_THREADS)
132
133void* align(size_t alignment, size_t size, void*& ptr, size_t& space) {
134 void* r = nullptr;
135 if (size <= space) {
136 char* p1 = static_cast<char*>(ptr);
137 char* p2 = reinterpret_cast<char*>(reinterpret_cast<uintptr_t>(p1 + (alignment - 1)) & -alignment);
138 size_t d = static_cast<size_t>(p2 - p1);
139 if (d <= space - size) {
140 r = p2;
141 ptr = r;
142 space -= d;
143 }
144 }
145 return r;
146}
147
148_LIBCPP_END_NAMESPACE_STD
149

source code of libcxx/src/memory.cpp