std::atomic_fetch_or,std::atomic_fetch_or_explicit(3)

NAME
std::atomic_fetch_or,std::atomic_fetch_or_explicit - std::atomic_fetch_or,std::atomic_fetch_or_explicit

Synopsis
   Defined in header <atomic>
   template< class T >
   T atomic_fetch_or( std::atomic<T>* obj,
   typename std::atomic<T>::value_type arg )
   noexcept;
   template< class T >
   T atomic_fetch_or( volatile std::atomic<T>*
   obj,
   typename std::atomic<T>::value_type arg )
   noexcept;
   template< class T > (1) (since C++11)
   T atomic_fetch_or_explicit( std::atomic<T>*
   obj,
   typename std::atomic<T>::value_type arg,
   std::memory_order order) noexcept; (2) (since C++11)
   template< class T >
   T atomic_fetch_or_explicit( volatile
   std::atomic<T>* obj,
   typename std::atomic<T>::value_type arg,
   std::memory_order order) noexcept;
   Atomically replaces the value pointed by obj with the result of bitwise OR between
   the old value of obj and arg. Returns the value obj held previously.
   The operation is performed as if the following is executed:
   1) obj->fetch_or(arg)
   2) obj->fetch_or(arg, order)
   If std::atomic<T> has no fetch_or member (this member is only provided for integral
   types), the program is ill-formed.

Parameters
   obj - pointer to the atomic object to modify
   arg - the value to bitwise OR to the value stored in the atomic object
   order - the memory synchronization ordering for this operation: all values are
           permitted.

Return value
   The value immediately preceding the effects of this function in the modification
   order of *obj.

Possible implementation
   template< class T >
   T atomic_fetch_or( std::atomic<T>* obj, typename std::atomic<T>::value_type arg )
   {
       return obj->fetch_or(arg);
   }

Example
// Run this code
 #include <iostream>
 #include <atomic>
 #include <thread>
 #include <chrono>
 #include <functional>
 // Binary semaphore for demonstrative purposes only
 // This is a simple yet meaningful example: atomic operations
 // are unnecessary without threads.
 class Semaphore {
     std::atomic_char m_signaled;
   public:
     Semaphore(bool initial = false)
     {
         m_signaled = initial;
     }
     // Block until semaphore is signaled
     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(); // signal printing to occur
                 m_count_sem.take(); // wait until printing is complete proceeding
             }
         }
         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();
 }

Output:
 10
 20
 30
 40
 50
 60
 70
 80
 90
 100
 print_count() done
 count_up() done
  Defect reports
   The following behavior-changing defect reports were applied retroactively to
   previously published C++ standards.
     DR Applied to Behavior as published Correct behavior
   P0558R1 C++11 exact type match required because T is T is deduced from the
                      deduced from multiple arguments atomic argument only

See also
                        atomically performs bitwise OR between the argument and
   fetch_or the value of the atomic object and obtains the value held
                        previously
                        (public member function of std::atomic<T>)
   atomic_fetch_and replaces the atomic object with the result of bitwise AND
   atomic_fetch_and_explicit with a non-atomic argument and obtains the previous value
   (C++11) of the atomic
   (C++11) (function template)
   atomic_fetch_xor replaces the atomic object with the result of bitwise XOR
   atomic_fetch_xor_explicit with a non-atomic argument and obtains the previous value
   (C++11) of the atomic
   (C++11) (function template)