C++ Atomic Library - Fetch And

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Description

It replaces the atomic object with the result of logical AND with a non-atomic argument and obtains the previous value of the atomic.

Declaration

Following is the declaration for std::atomic_fetch_and.

 template< class Integral > Integral atomic_fetch_and( volatile std::atomic>Integral>* obj, Integral arg ); 

C++11

 template< class Integral > Integral atomic_fetch_and( std::atomic<Integral>* obj, Integral arg ); 

Following is the declaration for std::atomic_fetch_and_explicit.

 template< class Integral > Integral atomic_fetch_and_explicit( std::atomic<Integral>* obj, Integral arg, std::memory_order order); 

C++11

 template< class Integral > Integral atomic_fetch_and_explicit( volatile std::atomic<Integral>* obj, Integral arg, std::memory_order order); 

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.

Return Value

It returns the value immediately preceding the effects of this function in the modification order of *obj.

Exceptions

No-noexcept − this member function never throws exceptions.

Example

In below example for std::atomic_fetch_and_explicit.

 #include <iostream> #include <atomic> #include <thread> #include <chrono> #include <functional> class Semaphore { std::atomic_char m_signaled; public: Semaphore(bool initial = false) { m_signaled = initial; } void take() { while (!std::atomic_fetch_and(&m_signaled, false)) { std::this_thread::sleep_for(std::chrono::milliseconds(10)); } } void put() { std::atomic_fetch_or(&m_signaled, true); } }; class ThreadedCounter { static const int N = 100; static const int REPORT_INTERVAL = 10; int m_count; bool m_done; Semaphore m_count_sem; Semaphore m_print_sem; void count_up() { for (m_count = 1; m_count <= N; m_count++) { if (m_count % REPORT_INTERVAL == 0) { if (m_count == N) m_done = true; m_print_sem.put(); m_count_sem.take(); } } std::cout << "count_up() done\n"; m_done = true; m_print_sem.put(); } void print_count() { do { m_print_sem.take(); std::cout << m_count << '\n'; m_count_sem.put(); } while (!m_done); std::cout << "print_count() done\n"; } public: ThreadedCounter() : m_done(false) {} void run() { auto print_thread = std::thread(&ThreadedCounter::print_count, this); auto count_thread = std::thread(&ThreadedCounter::count_up, this); print_thread.join(); count_thread.join(); } }; int main() { ThreadedCounter m_counter; m_counter.run(); }