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
28const allocator_arg_t allocator_arg = allocator_arg_t();
29
30bad_weak_ptr::~bad_weak_ptr() noexcept {}
31
32const char*
33bad_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)
47void
48__shared_count::__add_shared() noexcept
49{
50    __libcpp_atomic_refcount_increment(__shared_owners_);
51}
52
53bool
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
64void
65__shared_weak_count::__add_shared() noexcept
66{
67    __shared_count::__add_shared();
68}
69
70void
71__shared_weak_count::__add_weak() noexcept
72{
73    __libcpp_atomic_refcount_increment(__shared_weak_owners_);
74}
75
76void
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
84void
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
133const 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
141static constexpr std::size_t __sp_mut_count = 32;
142static 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
159void
160__sp_mut::lock() noexcept
161{
162    auto m = static_cast<__libcpp_mutex_t*>(__lx_);
163    __libcpp_mutex_lock(m);
164}
165
166void
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
190void*
191align(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<uintptr_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