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    std::atomic_...<std::shared_ptr>

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    Defined in header <memory> 
    template< class T >
bool atomic_is_lock_free( const std::shared_ptr<T>* p );
    		(1) (since C++11)
    (deprecated in C++20)
    (removed in C++26) 
    template< class T >
std::shared_ptr<T> atomic_load( const std::shared_ptr<T>* p );
    		(2) (since C++11)
    (deprecated in C++20)
    (removed in C++26) 
    template< class T >
std::shared_ptr<T> atomic_load_explicit
    ( const std::shared_ptr<T>* p, std::memory_order mo );
    		(3) (since C++11)
    (deprecated in C++20)
    (removed in C++26) 
    template< class T >
void atomic_store( std::shared_ptr<T>* p, std::shared_ptr<T> r );
    		(4) (since C++11)
    (deprecated in C++20)
    (removed in C++26) 
    template< class T >
void atomic_store_explicit
    ( std::shared_ptr<T>* p, std::shared_ptr<T> r,
      std::memory_order mo );
    		(5) (since C++11)
    (deprecated in C++20)
    (removed in C++26) 
    template< class T >
std::shared_ptr<T> atomic_exchange
    ( std::shared_ptr<T>* p, std::shared_ptr<T> r );
    		(6) (since C++11)
    (deprecated in C++20)
    (removed in C++26) 
    template< class T >
std::shared_ptr<T> atomic_exchange_explicit
    ( std::shared_ptr<T>* p, std::shared_ptr<T> r,
      std::memory_order mo );
    		(7) (since C++11)
    (deprecated in C++20)
    (removed in C++26) 
    template< class T >
bool atomic_compare_exchange_weak
    ( std::shared_ptr<T>* p, std::shared_ptr<T>* expected,
      std::shared_ptr<T> desired );
    		(8) (since C++11)
    (deprecated in C++20)
    (removed in C++26) 
    template< class T >
bool atomic_compare_exchange_strong
    ( std::shared_ptr<T>* p, std::shared_ptr<T>* expected,
      std::shared_ptr<T> desired );
    		(9) (since C++11)
    (deprecated in C++20)
    (removed in C++26) 
    template< class T >
bool atomic_compare_exchange_strong_explicit
    ( std::shared_ptr<T>* p, std::shared_ptr<T>* expected,
      std::shared_ptr<T> desired,
      std::memory_order success, std::memory_order failure );
    		(10) (since C++11)
    (deprecated in C++20)
    (removed in C++26) 
    template< class T >
bool atomic_compare_exchange_weak_explicit
    ( std::shared_ptr<T>* p, std::shared_ptr<T>* expected,
      std::shared_ptr<T> desired,
      std::memory_order success, std::memory_order failure );
    		(11) (since C++11)
    (deprecated in C++20)
    (removed in C++26)

    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, as if by p->swap(r).
    As with the non-specialized std::atomic_store_explicit, if mo is std::memory_order_acquire 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, as if by 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 std::atomic template: std::atomic<std::shared_ptr> and std::atomic<std::weak_ptr>.

    		(since C++20)
    (until C++26)

    These functions were removed in favor of the specializations of the std::atomic template: std::atomic<std::shared_ptr> and std::atomic<std::weak_ptr>.

    		(since C++26)

    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 2172 C++11 expected could be a null pointer the behavior is undefined in this case
    LWG 2980 C++11 empty shared_ptrs were never equivalent equivalent if they store the same pointer value

    See also

    (C++11)
    		 checks if the atomic type's operations are lock-free
    (function template) [edit]
    (C++11)(C++11)
    		 atomically replaces the value of the atomic object with a non-atomic argument
    (function template) [edit]
    (C++11)(C++11)
    		 atomically obtains the value stored in an atomic object
    (function template) [edit]
    (C++11)(C++11)
    		 atomically replaces the value of the atomic object with non-atomic argument and returns the old value of the atomic
    (function template) [edit]
    (C++11)(C++11)(C++11)(C++11)
    		 atomically compares the value of the atomic object with non-atomic argument and performs atomic exchange if equal or atomic load if not
    (function template) [edit]