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std::atomic_fetch_or, std::atomic_fetch_or_explicit

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Revision as of 14:58, 21 May 2013 by P12 (Talk | contribs)

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<td>
Defined in header <atomic>
</td>

<td></td> <td></td> <tr class="t-dcl ">

<td >
template< class Integral >
Integral atomic_fetch_or( std::atomic<Integral>* obj, Integral arg );
</td>

<td > (1) </td> <td > (since C++11) </td> </tr> <tr class="t-dcl ">

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

<td > (2) </td> <td > (since C++11) </td> </tr> <tr class="t-dcl ">

<td >
template< class Integral >

Integral atomic_fetch_or_explicit( std::atomic<Integral>* obj, Integral arg,

                                   std::memory_order order );
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<td > (3) </td> <td > (since C++11) </td> </tr> <tr class="t-dcl ">

<td >
template< class Integral >

Integral atomic_fetch_or_explicit( volatile std::atomic<Integral>* obj, Integral arg,

                                   std::memory_order order );
</td>

<td > (4) </td> <td > (since C++11) </td> </tr> Template:ddcl list end

1-2) Atomically replaces the value pointed by arg with the result of bitwise OR between the old value of obj and arg, and returns the value obj held previously, as if by obj->fetch_and(arg)

3-4) Atomically replaces the value pointed by arg with the result of bitwise OR between the old value of obj and arg, and returns the value obj held previously, as if by obj->fetch_and(arg, order)

Contents

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 sycnhronization ordering for this operation: all values are permitted.

Return value

The value held previously by the atomic object pointed to by obj

Exceptions

noexcept specification:  
noexcept
  

Possible implementation

template< class T >
typename std::enable_if<std::is_integral<T>::value && !std::is_same<T, bool>::value, T>::type
atomic_fetch_or( std::atomic<T>* obj, T arg );
{
    return obj->fetch_or(arg);
}

Example

#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

See also

Template:cpp/atomic/atomic/dcl list fetch orTemplate:cpp/atomic/dcl list atomic fetch andTemplate:cpp/atomic/dcl list atomic fetch xor
C documentation for atomic_fetch_or, atomic_fetch_or_explicit