LeetCode 1116. 打印零与奇偶数

题目链接：https://leetcode-cn.com/problems/print-zero-even-odd/

代码参考链接：https://leetcode-cn.com/problems/print-zero-even-odd/solution/c-san-chong-fang-shi-by-desaweis-imvm/

（1）原子操作解法：

#include<functional>
#include<mutex>
#include<thread>
#include<iostream>
 
using namespace std;
 
void printNumber(int value)
{
    cout << value;
}
 
class ZeroEvenOdd
{
private:
    int n;
    atomic<int> flag = 0;
 
public:
    ZeroEvenOdd(int n)
    {
        this->n = n;
    }
 
    // printNumber(x) outputs "x", where x is an integer.
    void zero(function<void(int)> printNumber)
    {
        for (int i = 1; i <= n; ++i)
        {
            while (flag != 0)
            {
                //告诉内核的调度器如果有其他进程/线程等待在这个CPU上运行，
                //则把CPU让给那些进程，即主动把时间片让出去，但如果本CPU上
                //只有我一个人在运行，没有其他人在等待运行，则调度器还是会
                //选中我来运行，也就是比较gentle的一个出让CPU。如果不执行yield，
                //则如果其他人有运行需求，则我一直尝试占着CPU运行，会导致他们的
                //响应时延变大（等到一个调度时间片后其他进程才有机会运行，现在我
                //yield了他们马上就能运行）。但如果没有其他人有需求，我可以一直占着CPU
                //（但是在过程中执行yield检查是否有其他人有运行需求）。
                //和睡眠的区别是睡眠必然等到指定时间后才重新调度我运行，
                //但yield只在其他人有运行需求的情况下才出让。
 
                this_thread::yield();
            }
 
            printNumber(0);
            if ((i & 0x1) == 0)
            {
                flag = 2;
            }
            else
            {
                flag = 1;
            }
        }
    }
 
    void even(function<void(int)> printNumber)
    {
        for (int i = 2; i <= n; i += 2)
        {
            while (flag != 2)
            {
                this_thread::yield();
            }
            printNumber(i);
            flag = 0;
        }
    }
 
    void odd(function<void(int)> printNumber)
    {
        for (int i = 1; i <= n; i += 2)
        {
            while (flag != 1)
            {
                this_thread::yield();
            }
            printNumber(i);
            flag = 0;
        }
    }
};
 
int main()
{
    ZeroEvenOdd myobj(5);
    thread myThread(&ZeroEvenOdd::zero, std::ref(myobj), printNumber);   //保证线程中用的同一个对象
    thread myThread2(&ZeroEvenOdd::even, std::ref(myobj), printNumber);
    thread myThread3(&ZeroEvenOdd::odd, std::ref(myobj), printNumber);
 
    myThread.join();
    myThread2.join();
    myThread3.join();
 
    return 0;
}

　（2）互斥锁+变量控制方法

#include<mutex>
#include<functional>
#include<thread>
#include<iostream>
 
using namespace std;
 
void printNumber(int value)
{
    cout << value;
}
 
class ZeroEvenOdd {
private:
    int n;
    mutex m;
    condition_variable cv;
    int flag = 0;
public:
    ZeroEvenOdd(int n) {
        this->n = n;
    }
 
    // printNumber(x) outputs "x", where x is an integer.
    void zero(function<void(int)> printNumber) {
        for (int i = 1; i <= n; ++i) {
            unique_lock<mutex> lock(m);
            cv.wait(lock, [&] {return flag == 0; });
            printNumber(0);
            if ((i & 0x1) == 0) //注意优先级，如果不确定可以加括号
            {
                flag = 2;
            }
            else {
                flag = 1;
            }
            cv.notify_all();
        }
    }
 
    void even(function<void(int)> printNumber) {
        for (int i = 2; i <= n; i += 2) {
            unique_lock<mutex> lock(m);
            cv.wait(lock, [&] {return flag == 2; });
            printNumber(i);
            flag = 0;
            cv.notify_all();
        }
    }
 
    void odd(function<void(int)> printNumber) {
        for (int i = 1; i <= n; i += 2) {
            unique_lock<mutex> lock(m);
            cv.wait(lock, [&] {return flag == 1; });
            printNumber(i);
            flag = 0;
            cv.notify_all();
        }
    }
};
 
int main()
{
    ZeroEvenOdd myobj(5);
    thread myThread(&ZeroEvenOdd::zero, std::ref(myobj), printNumber);   //保证线程中用的同一个对象
    thread myThread2(&ZeroEvenOdd::even, std::ref(myobj), printNumber);
    thread myThread3(&ZeroEvenOdd::odd, std::ref(myobj), printNumber);
 
    myThread.join();
    myThread2.join();
    myThread3.join();
 
    return 0;
}