text: //===------------------------ memory.cpp ----------------------------------===//
  //
  //                     The LLVM Compiler Infrastructure
  //
  // This file is dual licensed under the MIT and the University of Illinois Open
  // Source Licenses. See LICENSE.TXT for details.
  //
  //===----------------------------------------------------------------------===//
  
  #define _LIBCPP_BUILDING_MEMORY
  #include "memory"
  #ifndef _LIBCPP_HAS_NO_THREADS
  #include "mutex"
  #include "thread"
  #endif
  #include "support/atomic_support.h"
  
  _LIBCPP_BEGIN_NAMESPACE_STD
  
  namespace
  {
  
  // NOTE: Relaxed and acq/rel atomics (for increment and decrement respectively)
  // should be sufficient for thread safety.
  // See https://llvm.org/bugs/show_bug.cgi?id=22803
  template <class T>
  inline T
  increment(T& t) _NOEXCEPT
  {
      return __libcpp_atomic_add(&t, 1, _AO_Relaxed);
  }
  
  template <class T>
  inline T
  decrement(T& t) _NOEXCEPT
  {
      return __libcpp_atomic_add(&t, -1, _AO_Acq_Rel);
  }
  
  }  // namespace
  
  const allocator_arg_t allocator_arg = allocator_arg_t();
  
  bad_weak_ptr::~bad_weak_ptr() _NOEXCEPT {}
  
  const char*
  bad_weak_ptr::what() const _NOEXCEPT
  {
      return "bad_weak_ptr";
  }
  
  __shared_count::~__shared_count()
  {
  }
  
  void
  __shared_count::__add_shared() _NOEXCEPT
  {
      increment(__shared_owners_);
  }
  
  bool
  __shared_count::__release_shared() _NOEXCEPT
  {
      if (decrement(__shared_owners_) == -1)
      {
          __on_zero_shared();
          return true;
      }
      return false;
  }
  
  __shared_weak_count::~__shared_weak_count()
  {
  }
  
  void
  __shared_weak_count::__add_shared() _NOEXCEPT
  {
      __shared_count::__add_shared();
  }
  
  void
  __shared_weak_count::__add_weak() _NOEXCEPT
  {
      increment(__shared_weak_owners_);
  }
  
  void
  __shared_weak_count::__release_shared() _NOEXCEPT
  {
      if (__shared_count::__release_shared())
          __release_weak();
  }
  
  void
  __shared_weak_count::__release_weak() _NOEXCEPT
  {
      if (decrement(__shared_weak_owners_) == -1)
          __on_zero_shared_weak();
  }
  
  __shared_weak_count*
  __shared_weak_count::lock() _NOEXCEPT
  {
      long object_owners = __libcpp_atomic_load(&__shared_owners_);
      while (object_owners != -1)
      {
          if (__libcpp_atomic_compare_exchange(&__shared_owners_,
                                               &object_owners,
                                               object_owners+1))
              return this;
      }
      return 0;
  }
  
  #if !defined(_LIBCPP_NO_RTTI) || !defined(_LIBCPP_BUILD_STATIC)
  
  const void*
  __shared_weak_count::__get_deleter(const type_info&) const _NOEXCEPT
  {
      return 0;
  }
  
  #endif  // _LIBCPP_NO_RTTI
  
  #if defined(_LIBCPP_HAS_C_ATOMIC_IMP) && !defined(_LIBCPP_HAS_NO_THREADS)
  
  static const std::size_t __sp_mut_count = 16;
  static pthread_mutex_t mut_back_imp[__sp_mut_count] =
  {
      PTHREAD_MUTEX_INITIALIZER, PTHREAD_MUTEX_INITIALIZER, PTHREAD_MUTEX_INITIALIZER, PTHREAD_MUTEX_INITIALIZER,
      PTHREAD_MUTEX_INITIALIZER, PTHREAD_MUTEX_INITIALIZER, PTHREAD_MUTEX_INITIALIZER, PTHREAD_MUTEX_INITIALIZER,
      PTHREAD_MUTEX_INITIALIZER, PTHREAD_MUTEX_INITIALIZER, PTHREAD_MUTEX_INITIALIZER, PTHREAD_MUTEX_INITIALIZER,
      PTHREAD_MUTEX_INITIALIZER, PTHREAD_MUTEX_INITIALIZER, PTHREAD_MUTEX_INITIALIZER, PTHREAD_MUTEX_INITIALIZER
  };
  
  static mutex* mut_back = reinterpret_cast<std::mutex*>(mut_back_imp);
  
  _LIBCPP_CONSTEXPR __sp_mut::__sp_mut(void* p) _NOEXCEPT
     : __lx(p)
  {
  }
  
  void
  __sp_mut::lock() _NOEXCEPT
  {
      mutex& m = *static_cast<mutex*>(__lx);
      unsigned count = 0;
      while (!m.try_lock())
      {
          if (++count > 16)
          {
              m.lock();
              break;
          }
          this_thread::yield();
      }
  }
  
  void
  __sp_mut::unlock() _NOEXCEPT
  {
      static_cast<mutex*>(__lx)->unlock();
  }
  
  __sp_mut&
  __get_sp_mut(const void* p)
  {
      static __sp_mut muts[__sp_mut_count] 
      {
          &mut_back[ 0], &mut_back[ 1], &mut_back[ 2], &mut_back[ 3],
          &mut_back[ 4], &mut_back[ 5], &mut_back[ 6], &mut_back[ 7],
          &mut_back[ 8], &mut_back[ 9], &mut_back[10], &mut_back[11],
          &mut_back[12], &mut_back[13], &mut_back[14], &mut_back[15]
      };
      return muts[hash<const void*>()(p) & (__sp_mut_count-1)];
  }
  
  #endif // defined(_LIBCPP_HAS_C_ATOMIC_IMP) && !defined(_LIBCPP_HAS_NO_THREADS)
  
  void
  declare_reachable(void*)
  {
  }
  
  void
  declare_no_pointers(char*, size_t)
  {
  }
  
  void
  undeclare_no_pointers(char*, size_t)
  {
  }
  
  pointer_safety
  get_pointer_safety() _NOEXCEPT
  {
      return pointer_safety::relaxed;
  }
  
  void*
  __undeclare_reachable(void* p)
  {
      return p;
  }
  
  void*
  align(size_t alignment, size_t size, void*& ptr, size_t& space)
  {
      void* r = nullptr;
      if (size <= space)
      {
          char* p1 = static_cast<char*>(ptr);
          char* p2 = reinterpret_cast<char*>(reinterpret_cast<size_t>(p1 + (alignment - 1)) & -alignment);
          size_t d = static_cast<size_t>(p2 - p1);
          if (d <= space - size)
          {
              r = p2;
              ptr = r;
              space -= d;
          }
      }
      return r;
  }
  
  _LIBCPP_END_NAMESPACE_STD
  