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