std::atomic_...(3)

NAME
std::atomic_... - std::atomic_...

Synopsis
   Defined in header <memory>
                        (since C++11)
   template< class T > (1) (deprecated in
   bool atomic_is_lock_free( const std::shared_ptr<T>* p ); C++20)
                        (removed in C++26)
   template< class T > (since C++11)
   std::shared_ptr<T> atomic_load( const std::shared_ptr<T>* p (2) (deprecated in
   ); C++20)
                        (removed in C++26)
   template< class T > (since C++11)
                        (deprecated in
   std::shared_ptr<T> atomic_load_explicit (3) C++20)
                        (removed in C++26)
       ( const std::shared_ptr<T>* p, std::memory_order mo );
   template< class T > (since C++11)
   void atomic_store( std::shared_ptr<T>* p, (4) (deprecated in
   std::shared_ptr<T> r ); C++20)
                        (removed in C++26)
   template< class T >
                        (since C++11)
   void atomic_store_explicit (5) (deprecated in
       ( std::shared_ptr<T>* p, std::shared_ptr<T> r, C++20)
                        (removed in C++26)
         std::memory_order mo );
   template< class T > (since C++11)
                        (deprecated in
   std::shared_ptr<T> atomic_exchange (6) C++20)
                        (removed in C++26)
       ( std::shared_ptr<T>* p, std::shared_ptr<T> r );
   template< class T >
                        (since C++11)
   std::shared_ptr<T> atomic_exchange_explicit (7) (deprecated in
       ( std::shared_ptr<T>* p, std::shared_ptr<T> r, C++20)
                        (removed in C++26)
         std::memory_order mo );
   template< class T >
                        (since C++11)
   bool atomic_compare_exchange_weak (8) (deprecated in
       ( std::shared_ptr<T>* p, std::shared_ptr<T>* expected, C++20)
                        (removed in C++26)
         std::shared_ptr<T> desired );
   template< class T >
                        (since C++11)
   bool atomic_compare_exchange_strong (9) (deprecated in
       ( std::shared_ptr<T>* p, std::shared_ptr<T>* expected, C++20)
                        (removed in C++26)
         std::shared_ptr<T> desired );
   template< class T >
   bool atomic_compare_exchange_strong_explicit (since C++11)
       ( std::shared_ptr<T>* p, std::shared_ptr<T>* expected, (10) (deprecated in
         std::shared_ptr<T> desired, C++20)
                        (removed in C++26)
         std::memory_order success, std::memory_order failure
   );
   template< class T >
   bool atomic_compare_exchange_weak_explicit (since C++11)
       ( std::shared_ptr<T>* p, std::shared_ptr<T>* expected, (11) (deprecated in
         std::shared_ptr<T> desired, C++20)
                        (removed in C++26)
         std::memory_order success, std::memory_order failure
   );
   If multiple threads of execution access the same std::shared_ptr object without
   synchronization and any of those accesses uses a non-const member function of
   shared_ptr then a data race will occur unless all such access is performed through
   these functions, which are overloads of the corresponding atomic access functions
   (std::atomic_load, std::atomic_store, etc.).
   Note that the control block of a shared_ptr is thread-safe: different
   std::shared_ptr objects can be accessed using mutable operations, such as operator=
   or reset, simultaneously by multiple threads, even when these instances are copies,
   and share the same control block internally.
   1) Determines whether atomic access to the shared pointer pointed-to by p is
   lock-free.
   2) Equivalent to atomic_load_explicit(p, std::memory_order_seq_cst).
   3) Returns the shared pointer pointed-to by p.
   As with the non-specialized std::atomic_load_explicit, if mo is
   std::memory_order_release or std::memory_order_acq_rel, the behavior is undefined.
   4) Equivalent to atomic_store_explicit(p, r, std::memory_order_seq_cst).
   5) Stores the shared pointer r in the shared pointer pointed-to by p atomically,
   equivalent to p->swap(r).
   As with the non-specialized std::atomic_store_explicit, if mo is
   std::memory_order_release or std::memory_order_acq_rel, the behavior is undefined.
   6) Equivalent to atomic_exchange_explicit(p, r, std::memory_order_seq_cst).
   7) Stores the shared pointer r in the shared pointer pointed to by p and returns the
   value formerly pointed-to by p, atomically. Equivalent to p->swap(r) and returns a
   copy of r after the swap.
   8) Equivalent to
   atomic_compare_exchange_weak_explicit
       (p, expected, desired, std::memory_order_seq_cst,
                        std::memory_order_seq_cst).
   9) Equivalent to
   atomic_compare_exchange_strong_explicit
       (p, expected, desired, std::memory_order_seq_cst,
                        std::memory_order_seq_cst).
   10,11) Compares the shared pointers pointed-to by p and expected.
     * If they are equivalent (store the same pointer value, and either share ownership
       of the same object or are both empty), assigns desired into *p using the memory
       ordering constraints specified by success and returns true.
     * If they are not equivalent, assigns *p into *expected using the memory ordering
       constraints specified by failure and returns false.
   atomic_compare_exchange_weak_explicit may fail spuriously.
   If expected is a null pointer, or failure is std::memory_order_release or
   std::memory_order_acq_rel, the behavior is undefined.
   If p is a null pointer, the behaviors of these functions are all undefined.

Parameters
   p, expected - a pointer to a std::shared_ptr
   r, desired - a std::shared_ptr
   mo, success, failure - memory ordering selectors of type std::memory_order

Exceptions
   These functions do not throw exceptions.

Return value
   1) true if atomic access is implemented using lock-free instructions.
   2,3) A copy of the pointed-to shared pointer.
   4,5) (none)
   6,7) A copy of the formerly pointed-to shared pointer.
   8-11) true if the shared pointers were equivalent and the exchange was performed,
   false otherwise.

Notes
   These functions are typically implemented using mutexes, stored in a global hash
   table where the pointer value is used as the key.
   The Concurrency TS offers atomic smart pointer classes atomic_shared_ptr and
   atomic_weak_ptr as a replacement for the use of these functions.
   These functions were deprecated in favor of the specializations of the (since C++20)
   std::atomic template: std::atomic<std::shared_ptr> and (until C++26)
   std::atomic<std::weak_ptr>.
   These functions were removed in favor of the specializations of the
   std::atomic template: std::atomic<std::shared_ptr> and (since C++26)
   std::atomic<std::weak_ptr>.

Example
    This section is incomplete
    Reason: no example
   Defect reports
   The following behavior-changing defect reports were applied retroactively to
   previously published C++ standards.
      DR Applied to Behavior as published Correct behavior
   LWG 2980 C++11 empty shared_ptrs are never equivalent if they store the same
                       equivalent pointer value

See also
   atomic_is_lock_free checks if the atomic type's operations are
   (C++11) lock-free
                        (function template)
   atomic_store atomically replaces the value of the atomic
   atomic_store_explicit object with a non-atomic argument
   (C++11) (function template)
   (C++11)
   atomic_load atomically obtains the value stored in an
   atomic_load_explicit atomic object
   (C++11) (function template)
   (C++11)
   atomic_exchange atomically replaces the value of the atomic
   atomic_exchange_explicit object with non-atomic argument and returns
   (C++11) the old value of the atomic
   (C++11) (function template)
   atomic_compare_exchange_weak
   atomic_compare_exchange_weak_explicit atomically compares the value of the atomic
   atomic_compare_exchange_strong object with non-atomic argument and performs
   atomic_compare_exchange_strong_explicit atomic exchange if equal or atomic load if
   (C++11) not
   (C++11) (function template)
   (C++11)
   (C++11)

Category:
     * Todo no example