C++ Atomic Library - Compare Exchange

---

---

Description

It atomically compares the value of the atomic object with non-atomic argument and performs atomic exchange if equal or atomic load if not.

Declaration

Following is the declaration for std::atomic_compare_exchange_weak.

 template< class T > bool atomic_compare_exchange_weak( volatile std::atomic<T>* obj, T* expected, T desired ); 

C++11

 template< class T < bool atomic_compare_exchange_weak( std::atomic<T>* obj, T* expected, T desired ); 

Following is the declaration for std::atomic_compare_exchange_strong.

 template< class T > bool atomic_compare_exchange_strong( volatile std::atomic<T>* obj, T* expected, T desired ); 

C++11

 template< class T > bool atomic_compare_exchange_strong( std::atomic<T>* obj, T* expected, T desired ); 

Following is the declaration for std::atomic_compare_exchange_weak_explicit.

 template< class T > bool atomic_compare_exchange_weak_explicit( volatile std::atomic<T>* obj, T* expected, T desired, std::memory_order succ, std::memory_order fail ); 

C++11

 template< class T > bool atomic_compare_exchange_weak_explicit( std::atomic<T>* obj, T* expected, T desired, std::memory_order succ, std::memory_order fail ); 

Following is the declaration for std::atomic_compare_exchange_strong_explicit.

 template< class T > bool atomic_compare_exchange_strong_explicit( std::atomic<T>* obj, T* expected, T desired, std::memory_order succ, std::memory_order fail ); 

C++11

 template< class T > bool atomic_compare_exchange_strong_explicit( volatile std::atomic<T>* obj, T* expected, T desired, std::memory_order succ, std::memory_order fail ); 

Parameters

• obj − It is used in pointer to the atomic object to modify.

• desr − It is used to store the value in the atomic object.

• order − It is used to synchronise the memory ordering for this operation.

• succ − It is used in the memory synchronization ordering for the read-modify-write operation if the comparison succeeds. All values are permitted.

• fail − It is used in the memory synchronization ordering for the load operation if the comparison fails. Cannot be std::memory_order_release or std::memory_order_acq_rel and cannot specify stronger ordering than succ.

Return Value

It returns the result of the comparison: true if *obj was equal to *expected, false otherwise.

Exceptions

No-noexcept − this member function never throws exceptions.

Example

In below example for std::atomic_compare_exchange.

 #include <atomic> template<class T> struct node { T data; node* next; node(const T& data) : data(data), next(nullptr) {} }; template<class T> class stack { std::atomic<node<T>*> head; public: void push(const T& data) { node<T>* new_node = new node<T>(data); new_node->next = head.load(std::memory_order_relaxed); while(!std::atomic_compare_exchange_weak_explicit(&head, &new_node->next, new_node, std::memory_order_release, std::memory_order_relaxed)) ; } }; int main() { stack<int> s; s.push(1); s.push(2); s.push(3); }