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();
}
atomic.htm
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