contrib/libc++/src/memory.cpp

   1 //===------------------------ memory.cpp ----------------------------------===//
   2 //
   3 //                     The LLVM Compiler Infrastructure
   4 //
   5 // This file is dual licensed under the MIT and the University of Illinois Open
   6 // Source Licenses. See LICENSE.TXT for details.
   7 //
   8 //===----------------------------------------------------------------------===//
   9
  10 #include "memory"
  11 #ifndef _LIBCPP_HAS_NO_THREADS
  12 #include "mutex"
  13 #include "thread"
  14 #endif
  15 #include "include/atomic_support.h"
  16
  17 _LIBCPP_BEGIN_NAMESPACE_STD
  18
  19 const allocator_arg_t allocator_arg = allocator_arg_t();
  20
  21 bad_weak_ptr::~bad_weak_ptr() _NOEXCEPT {}
  22
  23 const char*
  24 bad_weak_ptr::what() const _NOEXCEPT
  25 {
  26     return "bad_weak_ptr";
  27 }
  28
  29 __shared_count::~__shared_count()
  30 {
  31 }
  32
  33 __shared_weak_count::~__shared_weak_count()
  34 {
  35 }
  36
  37 #if defined(_LIBCPP_DEPRECATED_ABI_LEGACY_LIBRARY_DEFINITIONS_FOR_INLINE_FUNCTIONS)
  38 void
  39 __shared_count::__add_shared() _NOEXCEPT
  40 {
  41     __libcpp_atomic_refcount_increment(__shared_owners_);
  42 }
  43
  44 bool
  45 __shared_count::__release_shared() _NOEXCEPT
  46 {
  47     if (__libcpp_atomic_refcount_decrement(__shared_owners_) == -1)
  48     {
  49         __on_zero_shared();
  50         return true;
  51     }
  52     return false;
  53 }
  54
  55 void
  56 __shared_weak_count::__add_shared() _NOEXCEPT
  57 {
  58     __shared_count::__add_shared();
  59 }
  60
  61 void
  62 __shared_weak_count::__add_weak() _NOEXCEPT
  63 {
  64     __libcpp_atomic_refcount_increment(__shared_weak_owners_);
  65 }
  66
  67 void
  68 __shared_weak_count::__release_shared() _NOEXCEPT
  69 {
  70     if (__shared_count::__release_shared())
  71         __release_weak();
  72 }
  73
  74 #endif // _LIBCPP_DEPRECATED_ABI_LEGACY_LIBRARY_DEFINITIONS_FOR_INLINE_FUNCTIONS
  75
  76 void
  77 __shared_weak_count::__release_weak() _NOEXCEPT
  78 {
  79     // NOTE: The acquire load here is an optimization of the very
  80     // common case where a shared pointer is being destructed while
  81     // having no other contended references.
  82     //
  83     // BENEFIT: We avoid expensive atomic stores like XADD and STREX
  84     // in a common case.  Those instructions are slow and do nasty
  85     // things to caches.
  86     //
  87     // IS THIS SAFE?  Yes.  During weak destruction, if we see that we
  88     // are the last reference, we know that no-one else is accessing
  89     // us. If someone were accessing us, then they would be doing so
  90     // while the last shared / weak_ptr was being destructed, and
  91     // that's undefined anyway.
  92     //
  93     // If we see anything other than a 0, then we have possible
  94     // contention, and need to use an atomicrmw primitive.
  95     // The same arguments don't apply for increment, where it is legal
  96     // (though inadvisable) to share shared_ptr references between
  97     // threads, and have them all get copied at once.  The argument
  98     // also doesn't apply for __release_shared, because an outstanding
  99     // weak_ptr::lock() could read / modify the shared count.
 100     if (__libcpp_atomic_load(&__shared_weak_owners_, _AO_Acquire) == 0)
 101     {
 102         // no need to do this store, because we are about
 103         // to destroy everything.
 104         //__libcpp_atomic_store(&__shared_weak_owners_, -1, _AO_Release);
 105         __on_zero_shared_weak();
 106     }
 107     else if (__libcpp_atomic_refcount_decrement(__shared_weak_owners_) == -1)
 108         __on_zero_shared_weak();
 109 }
 110
 111 __shared_weak_count*
 112 __shared_weak_count::lock() _NOEXCEPT
 113 {
 114     long object_owners = __libcpp_atomic_load(&__shared_owners_);
 115     while (object_owners != -1)
 116     {
 117         if (__libcpp_atomic_compare_exchange(&__shared_owners_,
 118                                              &object_owners,
 119                                              object_owners+1))
 120             return this;
 121     }
 122     return nullptr;
 123 }
 124
 125 #if !defined(_LIBCPP_NO_RTTI) || !defined(_LIBCPP_BUILD_STATIC)
 126
 127 const void*
 128 __shared_weak_count::__get_deleter(const type_info&) const _NOEXCEPT
 129 {
 130     return nullptr;
 131 }
 132
 133 #endif  // _LIBCPP_NO_RTTI
 134
 135 #if !defined(_LIBCPP_HAS_NO_ATOMIC_HEADER)
 136
 137 _LIBCPP_SAFE_STATIC static const std::size_t __sp_mut_count = 16;
 138 _LIBCPP_SAFE_STATIC static __libcpp_mutex_t mut_back[__sp_mut_count] =
 139 {
 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     _LIBCPP_MUTEX_INITIALIZER, _LIBCPP_MUTEX_INITIALIZER, _LIBCPP_MUTEX_INITIALIZER, _LIBCPP_MUTEX_INITIALIZER,
 143     _LIBCPP_MUTEX_INITIALIZER, _LIBCPP_MUTEX_INITIALIZER, _LIBCPP_MUTEX_INITIALIZER, _LIBCPP_MUTEX_INITIALIZER
 144 };
 145
 146 _LIBCPP_CONSTEXPR __sp_mut::__sp_mut(void* p) _NOEXCEPT
 147    : __lx(p)
 148 {
 149 }
 150
 151 void
 152 __sp_mut::lock() _NOEXCEPT
 153 {
 154     auto m = static_cast<__libcpp_mutex_t*>(__lx);
 155     unsigned count = 0;
 156     while (!__libcpp_mutex_trylock(m))
 157     {
 158         if (++count > 16)
 159         {
 160             __libcpp_mutex_lock(m);
 161             break;
 162         }
 163         this_thread::yield();
 164     }
 165 }
 166
 167 void
 168 __sp_mut::unlock() _NOEXCEPT
 169 {
 170     __libcpp_mutex_unlock(static_cast<__libcpp_mutex_t*>(__lx));
 171 }
 172
 173 __sp_mut&
 174 __get_sp_mut(const void* p)
 175 {
 176     static __sp_mut muts[__sp_mut_count]
 177     {
 178         &mut_back[ 0], &mut_back[ 1], &mut_back[ 2], &mut_back[ 3],
 179         &mut_back[ 4], &mut_back[ 5], &mut_back[ 6], &mut_back[ 7],
 180         &mut_back[ 8], &mut_back[ 9], &mut_back[10], &mut_back[11],
 181         &mut_back[12], &mut_back[13], &mut_back[14], &mut_back[15]
 182     };
 183     return muts[hash<const void*>()(p) & (__sp_mut_count-1)];
 184 }
 185
 186 #endif // !defined(_LIBCPP_HAS_NO_ATOMIC_HEADER)
 187
 188 void
 189 declare_reachable(void*)
 190 {
 191 }
 192
 193 void
 194 declare_no_pointers(char*, size_t)
 195 {
 196 }
 197
 198 void
 199 undeclare_no_pointers(char*, size_t)
 200 {
 201 }
 202
 203 #if !defined(_LIBCPP_ABI_POINTER_SAFETY_ENUM_TYPE)
 204 pointer_safety get_pointer_safety() _NOEXCEPT
 205 {
 206     return pointer_safety::relaxed;
 207 }
 208 #endif
 209
 210 void*
 211 __undeclare_reachable(void* p)
 212 {
 213     return p;
 214 }
 215
 216 void*
 217 align(size_t alignment, size_t size, void*& ptr, size_t& space)
 218 {
 219     void* r = nullptr;
 220     if (size <= space)
 221     {
 222         char* p1 = static_cast<char*>(ptr);
 223         char* p2 = reinterpret_cast<char*>(reinterpret_cast<size_t>(p1 + (alignment - 1)) & -alignment);
 224         size_t d = static_cast<size_t>(p2 - p1);
 225         if (d <= space - size)
 226         {
 227             r = p2;
 228             ptr = r;
 229             space -= d;
 230         }
 231     }
 232     return r;
 233 }
 234
 235 _LIBCPP_END_NAMESPACE_STD