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std::atomic_...(3) C++ Standard Libary 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) (re- moved 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) (re- moved in C++26) template< class T > (since C++11) (dep- recated in std::shared_ptr<T> atomic_load_explicit (3) C++20) (re- moved 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) (re- moved 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) (re- moved in C++26) std::memory_order mo ); template< class T > (since C++11) (dep- recated in std::shared_ptr<T> atomic_exchange (6) C++20) (re- moved 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) (re- moved 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) (re- moved 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) (re- moved 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) (re- moved 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) (re- moved in C++26) std::memory_order success, std::memory_order failure ); If multiple threads of execution access the same std::shared_ptr ob- ject 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 ac- cess functions (std::atomic_load, std::atomic_store, etc.). Note that the control block of a shared_ptr is thread-safe: differ- ent std::shared_ptr objects can be accessed using mutable operations, such as operator= or reset, simultaneously by multiple threads, even when these in- stances 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_or- der_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_or- der_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_re- lease or std::memory_order_acq_rel, the behavior is undefined. If p is a null pointer, the behaviors of these functions are all un- defined. 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::mem- ory_order Exceptions These functions do not throw exceptions. Return value 1) true if atomic access is implemented using lock-free instruc- tions. 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 retroac- tively 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 ar- gument (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 argu- ment 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 argu- ment 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 http://cppreference.com 2024.06.10 std::atomic_...(3)
NAME | Synopsis | Parameters | Exceptions | Return value | Notes | Example | See also | Category:
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