c++11標準庫學習 atomic

// c++11 標準庫使用atomic 自旋鎖(只要有鎖阻塞等待的鎖)
#include <iostream>       
#include <atomic>         
#include <thread>         
#include <vector>         
#include <sstream>        
//使用宏賦初值
std::atomic_flag lock_stream = ATOMIC_FLAG_INIT;
std::stringstream stream;

void append_number(int x) {
    //test_and_set() 成功設置說明沒有互斥返回false,設置不成功返回false繼續while循環形成自旋鎖
    while (lock_stream.test_and_set()) 
    {
        std::cout << "test_and_set" << std::endl;
    }
    stream << "thread #" << x << '\n';
    //清除鎖
    lock_stream.clear();
}

int main()
{
    std::vector<std::thread> threads;
    for (int i = 1; i <= 10; ++i) threads.push_back(std::thread(append_number, i));
    for (auto& th : threads) th.join();

    std::cout << stream.str();
    return 0;
}

std::this_thread::yield(); 的使用

//10個線程競爭看哪一個執行打印語句
#include <iostream>       // std::cout
#include <atomic>         // std::atomic, std::atomic_flag, ATOMIC_FLAG_INIT
#include <thread>         // std::thread, std::this_thread::yield
#include <vector>         // std::vector

std::atomic<bool> ready(false);
std::atomic_flag winner = ATOMIC_FLAG_INIT;

void count1m(int id) {
    while (!ready) 
    { 
        //當前線程放棄執行，操作系統調度另一線程繼續執行。
        //即當前線程將未使用完的“CPU時間片”讓給其他線程使用，
        //等其他線程使用完後再與其他線程一起競爭"CPU"
        std::this_thread::yield(); 
    }    
    for (int i = 0; i < 1000000; ++i) {} 
    if (!winner.test_and_set()) 
    { 
        std::cout << "thread #" << id << " 線程成功打印!\n"; 
    }
};

int main()
{
    std::vector<std::thread> threads;
    std::cout << "10個線程 每個執行1百萬for循環...\n";
    for (int i = 1; i <= 10; ++i) threads.push_back(std::thread(count1m, i));
    ready = true;
    for (auto& th : threads) th.join();

    return 0;
}