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

template< class T > bool atomic_is_lock_free( const std::shared_ptr<T>* p );	(1)	(since C++11)
template< class T > std::shared_ptr<T> atomic_load( const std::shared_ptr<T>* p );	(2)	(since C++11)
template< class T > std::shared_ptr<T> atomic_load_explicit( const std::shared_ptr<T>* p, std::memory_order mo );	(3)	(since C++11)
template< class T > void atomic_store( std::shared_ptr<T>* p, std::shared_ptr<T> r );	(4)	(since C++11)
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)
template< class T > std::shared_ptr<T> atomic_exchange( std::shared_ptr<T>* p, std::shared_ptr<T> r);	(6)	(since C++11)
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)
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)
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)
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)
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)

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, mo cannot be std::memory_order_release or std::memory_order_acq_rel

4) Equivalent to atomic_store_explicit(p, r, memory_order_seq_cst)

5) Stores the shared pointer r in the shared pointer pointed-to by p atomically, effectively executing p->swap(r). As with the non-specialized std::atomic_store_explicit, mo cannot be std::memory_order_acquire or std::memory_order_acq_rel.

6) Equivalent to atomic_exchange_explicit(p, r, 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. Effectively executes 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) Compares the shared pointers pointed-to by p and expected. If they are equivalent (share ownership of the same pointer and refer to the same pointer), 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.

11) Same as 10), but may fail spuriously.

All these functions invoke undefined behavior if p is a null pointer.

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

8,9,10,11) true if the shared pointers were equivalent and the exchange was performed, false otherwise.

Notes

The Concurrency TS offers atomic smart pointer classes atomic_shared_ptr and atomic_weak_ptr as a replacement for the use of these functions.

atomic_is_lock_free (C++11)	checks if the atomic type's operations are lock-free (function template)
atomic_storeatomic_store_explicit (C++11)(C++11)	atomically replaces the value of the atomic object with a non-atomic argument (function template)
atomic_loadatomic_load_explicit (C++11)(C++11)	atomically obtains the value stored in an atomic object (function template)
atomic_exchangeatomic_exchange_explicit (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)
atomic_compare_exchange_weakatomic_compare_exchange_weak_explicitatomic_compare_exchange_strongatomic_compare_exchange_strong_explicit (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)