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题目：实现两个线程，一个打印奇数，一个打印偶数

思路（1）：用c++11的互斥量mutex,条件变量condition_variable.一个全局变量i,控制每个线程获取互斥锁后执行一次，再通过条件变量唤醒另一个等在该锁上的线程，让其执行，即保证两个线程交替运行。

#include <thread>
#include <iostream>
#include <mutex>
#include <condition_variable>
#include <windows.h>
std::mutex data_mutex;
std::condition_variable data_var;
bool flag = true;
int i = 0;void printA()
{while (1){Sleep(1000);unique_lock<mutex> lck(data_mutex);data_var.wait(lck, [] {return flag; });//只有return flag==true时才不阻塞，上锁成功cout << "thread: " << this_thread::get_id() << "   printf: " << i << endl;i += 1;flag = false;data_var.notify_one();//释放锁，并唤醒等在该锁上的线程}
}void printB()
{while (1){unique_lock<mutex> lck(data_mutex);data_var.wait(lck, []{return !flag; });cout << "thread: " << this_thread::get_id() << "   printf: " << i << endl;i += 1;flag = true;data_var.notify_one();}
}

思路（2）：直接用一个全局的flag来控制两个线程交替运行，一个线程在flag==true可以执行，另一个线程在flag==false的时候执行。

void printA()
{while (1){Sleep(1000);if (flag){cout << "thread: " << this_thread::get_id() << "   printf: " << i << endl;i += 1;flag = false;}}
}void printB()
{while (1){if (!flag){cout << "thread: " << this_thread::get_id() << "   printf: " << i << endl;i += 1;flag = true;}}
}