151 lines · cpp
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-exception6//7//===----------------------------------------------------------------------===//8 9#include <__config>10#ifdef _LIBCPP_DEPRECATED_ABI_LEGACY_LIBRARY_DEFINITIONS_FOR_INLINE_FUNCTIONS11# define _LIBCPP_SHARED_PTR_DEFINE_LEGACY_INLINE_FUNCTIONS12#endif13 14#include <__functional/hash.h>15#include <memory>16#include <typeinfo>17 18#if _LIBCPP_HAS_THREADS19# include <mutex>20# include <thread>21# if defined(__ELF__) && defined(_LIBCPP_LINK_PTHREAD_LIB)22# pragma comment(lib, "pthread")23# endif24#endif25 26#include "include/atomic_support.h"27 28_LIBCPP_BEGIN_NAMESPACE_STD29 30bad_weak_ptr::~bad_weak_ptr() noexcept {}31 32const char* bad_weak_ptr::what() const noexcept { return "bad_weak_ptr"; }33 34__shared_count::~__shared_count() {}35 36__shared_weak_count::~__shared_weak_count() {}37 38#if defined(_LIBCPP_SHARED_PTR_DEFINE_LEGACY_INLINE_FUNCTIONS)39void __shared_count::__add_shared() noexcept { __libcpp_atomic_refcount_increment(__shared_owners_); }40 41bool __shared_count::__release_shared() noexcept {42 if (__libcpp_atomic_refcount_decrement(__shared_owners_) == -1) {43 __on_zero_shared();44 return true;45 }46 return false;47}48 49void __shared_weak_count::__add_shared() noexcept { __shared_count::__add_shared(); }50 51void __shared_weak_count::__add_weak() noexcept { __libcpp_atomic_refcount_increment(__shared_weak_owners_); }52 53void __shared_weak_count::__release_shared() noexcept {54 if (__shared_count::__release_shared())55 __release_weak();56}57#endif // _LIBCPP_SHARED_PTR_DEFINE_LEGACY_INLINE_FUNCTIONS58 59void __shared_weak_count::__release_weak() noexcept {60 // NOTE: The acquire load here is an optimization of the very61 // common case where a shared pointer is being destructed while62 // having no other contended references.63 //64 // BENEFIT: We avoid expensive atomic stores like XADD and STREX65 // in a common case. Those instructions are slow and do nasty66 // things to caches.67 //68 // IS THIS SAFE? Yes. During weak destruction, if we see that we69 // are the last reference, we know that no-one else is accessing70 // us. If someone were accessing us, then they would be doing so71 // while the last shared / weak_ptr was being destructed, and72 // that's undefined anyway.73 //74 // If we see anything other than a 0, then we have possible75 // contention, and need to use an atomicrmw primitive.76 // The same arguments don't apply for increment, where it is legal77 // (though inadvisable) to share shared_ptr references between78 // threads, and have them all get copied at once. The argument79 // also doesn't apply for __release_shared, because an outstanding80 // weak_ptr::lock() could read / modify the shared count.81 if (__libcpp_atomic_load(&__shared_weak_owners_, _AO_Acquire) == 0) {82 // no need to do this store, because we are about83 // to destroy everything.84 //__libcpp_atomic_store(&__shared_weak_owners_, -1, _AO_Release);85 __on_zero_shared_weak();86 } else if (__libcpp_atomic_refcount_decrement(__shared_weak_owners_) == -1)87 __on_zero_shared_weak();88}89 90__shared_weak_count* __shared_weak_count::lock() noexcept {91 long object_owners = __libcpp_atomic_load(&__shared_owners_);92 while (object_owners != -1) {93 if (__libcpp_atomic_compare_exchange(&__shared_owners_, &object_owners, object_owners + 1))94 return this;95 }96 return nullptr;97}98 99const void* __shared_weak_count::__get_deleter(const type_info&) const noexcept { return nullptr; }100 101#if _LIBCPP_HAS_THREADS102 103static constexpr std::size_t __sp_mut_count = 32;104static constinit __libcpp_mutex_t mut_back[__sp_mut_count] = {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 _LIBCPP_MUTEX_INITIALIZER, _LIBCPP_MUTEX_INITIALIZER, _LIBCPP_MUTEX_INITIALIZER, _LIBCPP_MUTEX_INITIALIZER,112 _LIBCPP_MUTEX_INITIALIZER, _LIBCPP_MUTEX_INITIALIZER, _LIBCPP_MUTEX_INITIALIZER, _LIBCPP_MUTEX_INITIALIZER};113 114constexpr __sp_mut::__sp_mut(void* p) noexcept : __lx_(p) {}115 116void __sp_mut::lock() noexcept {117 auto m = static_cast<__libcpp_mutex_t*>(__lx_);118 __libcpp_mutex_lock(m);119}120 121void __sp_mut::unlock() noexcept { __libcpp_mutex_unlock(static_cast<__libcpp_mutex_t*>(__lx_)); }122 123__sp_mut& __get_sp_mut(const void* p) {124 static constinit __sp_mut muts[__sp_mut_count] = {125 &mut_back[0], &mut_back[1], &mut_back[2], &mut_back[3], &mut_back[4], &mut_back[5], &mut_back[6],126 &mut_back[7], &mut_back[8], &mut_back[9], &mut_back[10], &mut_back[11], &mut_back[12], &mut_back[13],127 &mut_back[14], &mut_back[15], &mut_back[16], &mut_back[17], &mut_back[18], &mut_back[19], &mut_back[20],128 &mut_back[21], &mut_back[22], &mut_back[23], &mut_back[24], &mut_back[25], &mut_back[26], &mut_back[27],129 &mut_back[28], &mut_back[29], &mut_back[30], &mut_back[31]};130 return muts[hash<const void*>()(p) & (__sp_mut_count - 1)];131}132 133#endif // _LIBCPP_HAS_THREADS134 135void* align(size_t alignment, size_t size, void*& ptr, size_t& space) {136 void* r = nullptr;137 if (size <= space) {138 char* p1 = static_cast<char*>(ptr);139 char* p2 = reinterpret_cast<char*>(reinterpret_cast<uintptr_t>(p1 + (alignment - 1)) & -alignment);140 size_t d = static_cast<size_t>(p2 - p1);141 if (d <= space - size) {142 r = p2;143 ptr = r;144 space -= d;145 }146 }147 return r;148}149 150_LIBCPP_END_NAMESPACE_STD151