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1469. atomic<T*> inheritance from atomic_address breaks type safety

Section: 32.5.8 [atomics.types.generic] Status: Resolved Submitter: BSI Opened: 2010-08-25 Last modified: 2016-01-28

Priority: Not Prioritized

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Discussion:

Addresses GB-133

The free functions that operate on atomic_address can be used to store a pointer to an unrelated type in an atomic<T*> without a cast. e.g.

int i;
atomic<int*> ai(&i);
string s;
atomic_store(&ai,&s);

Overload the atomic_store, atomic_exchange and atomic_compare_exchange_[weak/strong] operations for atomic<T*> to allow storing only pointers to T.

[ 2010-10-27 Daniel adds: ]

Resolving this issue will also solve 1467⁽ⁱ⁾

Accepting n3164 would solve this issue by removing atomic_address.

[Resolved in Batavia by accepting n3193. ]

Proposed resolution:

Add the following overloads to 32.5.8 [atomics.types.generic], the synopsis around the specialization atomic<T*>, as indicated:

namespace std {
  [..]
  template <class T> struct atomic<T*> : atomic_address {
    [..]
  };

  template<typename T>
  void atomic_store(atomic<T*>&,T*);
  template<typename T>
  void atomic_store(atomic<T*>&,void*) = delete;
  template<typename T>
  void atomic_store_explicit(atomic<T*>&,T*,memory_order);
  template<typename T>
  void atomic_store_explicit(atomic<T*>&,void*,memory_order) = delete;
  template<typename T>
  T* atomic_exchange(atomic<T*>&,T*);
  template<typename T>
  T* atomic_exchange(atomic<T*>&,void*) = delete;
  template<typename T>
  T* atomic_exchange_explicit(atomic<T*>&,T*,memory_order);
  template<typename T>
  T* atomic_exchange_explicit(atomic<T*>&,void*,memory_order) = delete;
  template<typename T>
  T* atomic_compare_exchange_weak(atomic<T*>&,T**,T*);
  template<typename T>
  T* atomic_compare_exchange_weak(atomic<T*>&,void**,void*) = delete;
  template<typename T>
  T* atomic_compare_exchange_weak_explicit(atomic<T*>&,T**,T*,memory_order);
  template<typename T>
  T* atomic_compare_exchange_weak_explicit(atomic<T*>&,void**,void*,memory_order) = delete;
  template<typename T>
  T* atomic_compare_exchange_strong(atomic<T*>&,T**,T*);
  template<typename T>
  T* atomic_compare_exchange_strong(atomic<T*>&,void**,void*) = delete;
  template<typename T>
  T* atomic_compare_exchange_strong_explicit(atomic<T*>&,T**,T*,memory_order);
  template<typename T>
  T* atomic_compare_exchange_strong_explicit(atomic<T*>&,void**,void*,memory_order) = delete;

}