libcxx/src/memory.cpp

   1 //===------------------------ memory.cpp ----------------------------------===//
   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 "memory"
  10 #ifndef _LIBCPP_HAS_NO_THREADS
  11 #include "mutex"
  12 #include "thread"
  13 #if defined(__ELF__) && defined(_LIBCPP_LINK_PTHREAD_LIB)
  14 #pragma comment(lib, "pthread")
  15 #endif
  16 #endif
  17 #include "include/atomic_support.h"
  18
  19 _LIBCPP_BEGIN_NAMESPACE_STD
  20
  21 const allocator_arg_t allocator_arg = allocator_arg_t();
  22
  23 bad_weak_ptr::~bad_weak_ptr() _NOEXCEPT {}
  24
  25 const char*
  26 bad_weak_ptr::what() const _NOEXCEPT
  27 {
  28     return "bad_weak_ptr";
  29 }
  30
  31 __shared_count::~__shared_count()
  32 {
  33 }
  34
  35 __shared_weak_count::~__shared_weak_count()
  36 {
  37 }
  38
  39 #if defined(_LIBCPP_DEPRECATED_ABI_LEGACY_LIBRARY_DEFINITIONS_FOR_INLINE_FUNCTIONS)
  40 void
  41 __shared_count::__add_shared() _NOEXCEPT
  42 {
  43     __libcpp_atomic_refcount_increment(__shared_owners_);
  44 }
  45
  46 bool
  47 __shared_count::__release_shared() _NOEXCEPT
  48 {
  49     if (__libcpp_atomic_refcount_decrement(__shared_owners_) == -1)
  50     {
  51         __on_zero_shared();
  52         return true;
  53     }
  54     return false;
  55 }
  56
  57 void
  58 __shared_weak_count::__add_shared() _NOEXCEPT
  59 {
  60     __shared_count::__add_shared();
  61 }
  62
  63 void
  64 __shared_weak_count::__add_weak() _NOEXCEPT
  65 {
  66     __libcpp_atomic_refcount_increment(__shared_weak_owners_);
  67 }
  68
  69 void
  70 __shared_weak_count::__release_shared() _NOEXCEPT
  71 {
  72     if (__shared_count::__release_shared())
  73         __release_weak();
  74 }
  75
  76 #endif // _LIBCPP_DEPRECATED_ABI_LEGACY_LIBRARY_DEFINITIONS_FOR_INLINE_FUNCTIONS
  77
  78 void
  79 __shared_weak_count::__release_weak() _NOEXCEPT
  80 {
  81     // NOTE: The acquire load here is an optimization of the very
  82     // common case where a shared pointer is being destructed while
  83     // having no other contended references.
  84     //
  85     // BENEFIT: We avoid expensive atomic stores like XADD and STREX
  86     // in a common case.  Those instructions are slow and do nasty
  87     // things to caches.
  88     //
  89     // IS THIS SAFE?  Yes.  During weak destruction, if we see that we
  90     // are the last reference, we know that no-one else is accessing
  91     // us. If someone were accessing us, then they would be doing so
  92     // while the last shared / weak_ptr was being destructed, and
  93     // that's undefined anyway.
  94     //
  95     // If we see anything other than a 0, then we have possible
  96     // contention, and need to use an atomicrmw primitive.
  97     // The same arguments don't apply for increment, where it is legal
  98     // (though inadvisable) to share shared_ptr references between
  99     // threads, and have them all get copied at once.  The argument
 100     // also doesn't apply for __release_shared, because an outstanding
 101     // weak_ptr::lock() could read / modify the shared count.
 102     if (__libcpp_atomic_load(&__shared_weak_owners_, _AO_Acquire) == 0)
 103     {
 104         // no need to do this store, because we are about
 105         // to destroy everything.
 106         //__libcpp_atomic_store(&__shared_weak_owners_, -1, _AO_Release);
 107         __on_zero_shared_weak();
 108     }
 109     else if (__libcpp_atomic_refcount_decrement(__shared_weak_owners_) == -1)
 110         __on_zero_shared_weak();
 111 }
 112
 113 __shared_weak_count*
 114 __shared_weak_count::lock() _NOEXCEPT
 115 {
 116     long object_owners = __libcpp_atomic_load(&__shared_owners_);
 117     while (object_owners != -1)
 118     {
 119         if (__libcpp_atomic_compare_exchange(&__shared_owners_,
 120                                              &object_owners,
 121                                              object_owners+1))
 122             return this;
 123     }
 124     return nullptr;
 125 }
 126
 127 const void*
 128 __shared_weak_count::__get_deleter(const type_info&) const _NOEXCEPT
 129 {
 130     return nullptr;
 131 }
 132
 133 #if !defined(_LIBCPP_HAS_NO_ATOMIC_HEADER)
 134
 135 _LIBCPP_SAFE_STATIC static const std::size_t __sp_mut_count = 16;
 136 _LIBCPP_SAFE_STATIC static __libcpp_mutex_t mut_back[__sp_mut_count] =
 137 {
 138     _LIBCPP_MUTEX_INITIALIZER, _LIBCPP_MUTEX_INITIALIZER, _LIBCPP_MUTEX_INITIALIZER, _LIBCPP_MUTEX_INITIALIZER,
 139     _LIBCPP_MUTEX_INITIALIZER, _LIBCPP_MUTEX_INITIALIZER, _LIBCPP_MUTEX_INITIALIZER, _LIBCPP_MUTEX_INITIALIZER,
 140     _LIBCPP_MUTEX_INITIALIZER, _LIBCPP_MUTEX_INITIALIZER, _LIBCPP_MUTEX_INITIALIZER, _LIBCPP_MUTEX_INITIALIZER,
 141     _LIBCPP_MUTEX_INITIALIZER, _LIBCPP_MUTEX_INITIALIZER, _LIBCPP_MUTEX_INITIALIZER, _LIBCPP_MUTEX_INITIALIZER
 142 };
 143
 144 _LIBCPP_CONSTEXPR __sp_mut::__sp_mut(void* p) _NOEXCEPT
 145    : __lx(p)
 146 {
 147 }
 148
 149 void
 150 __sp_mut::lock() _NOEXCEPT
 151 {
 152     auto m = static_cast<__libcpp_mutex_t*>(__lx);
 153     unsigned count = 0;
 154     while (!__libcpp_mutex_trylock(m))
 155     {
 156         if (++count > 16)
 157         {
 158             __libcpp_mutex_lock(m);
 159             break;
 160         }
 161         this_thread::yield();
 162     }
 163 }
 164
 165 void
 166 __sp_mut::unlock() _NOEXCEPT
 167 {
 168     __libcpp_mutex_unlock(static_cast<__libcpp_mutex_t*>(__lx));
 169 }
 170
 171 __sp_mut&
 172 __get_sp_mut(const void* p)
 173 {
 174     static __sp_mut muts[__sp_mut_count]
 175     {
 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     };
 181     return muts[hash<const void*>()(p) & (__sp_mut_count-1)];
 182 }
 183
 184 #endif // !defined(_LIBCPP_HAS_NO_ATOMIC_HEADER)
 185
 186 void
 187 declare_reachable(void*)
 188 {
 189 }
 190
 191 void
 192 declare_no_pointers(char*, size_t)
 193 {
 194 }
 195
 196 void
 197 undeclare_no_pointers(char*, size_t)
 198 {
 199 }
 200
 201 #if !defined(_LIBCPP_ABI_POINTER_SAFETY_ENUM_TYPE)
 202 pointer_safety get_pointer_safety() _NOEXCEPT
 203 {
 204     return pointer_safety::relaxed;
 205 }
 206 #endif
 207
 208 void*
 209 __undeclare_reachable(void* p)
 210 {
 211     return p;
 212 }
 213
 214 void*
 215 align(size_t alignment, size_t size, void*& ptr, size_t& space)
 216 {
 217     void* r = nullptr;
 218     if (size <= space)
 219     {
 220         char* p1 = static_cast<char*>(ptr);
 221         char* p2 = reinterpret_cast<char*>(reinterpret_cast<size_t>(p1 + (alignment - 1)) & -alignment);
 222         size_t d = static_cast<size_t>(p2 - p1);
 223         if (d <= space - size)
 224         {
 225             r = p2;
 226             ptr = r;
 227             space -= d;
 228         }
 229     }
 230     return r;
 231 }
 232
 233 _LIBCPP_END_NAMESPACE_STD