【C++编程】exchange 函数详解

 

 https://www.jianshu.com/u/9456fecb5f96

 

#include <algorithm>
#include <atomic>
#include <cstddef>
#include <iostream>
#include <thread>
#include <vector>
#include <mutex>

int main()
{
    const std::size_t ThreadNumber = 5;
    const int Sum = 2;
    std::atomic<int> atom{0};
    std::atomic<int> counter{0};
    std::mutex flush;

    auto lambda = [&](const int id)
    {
        for (int next = 0; next < Sum; ++next)
        {
            const int current = atom.exchange(next);
            counter++;
            {
                std::lock_guard<std::mutex> lg(flush);
                std::cout << '#' << id << " (" << std::this_thread::get_id()
                                    << ") wrote " << next << " replacing the old value " << current << '\n';
            }
        }
    };

    std::vector<std::thread> v;
    for (std::size_t i = 0; i < ThreadNumber; ++i)
        v.emplace_back(lambda, i);

    for (auto &tr : v)
        tr.join();

    std::cout << ThreadNumber << " threads adding 0 to "
                        << Sum << " takes total " << counter << " times\n";
}

 

template< class T, class U = T >
T exchange( T& obj, U&& new_value );

 

template< class T, class U = T > T exchange( T& obj, U&& new_value );

(since C++14)