https://blog.csdn.net/dcrmg/article/details/53912941
多线程操作的thread类，简单多线程示例：
#include <iostream>
#include <thread>
#include <Windows.h>
using namespace std;
void thread01()
{
for (int i = 0; i < 5; i++)
{
cout << "Thread 01 is working ！" << endl;
Sleep(100);
}
}
void thread02()
{
for (int i = 0; i < 5; i++)
{
cout << "Thread 02 is working ！" << endl;
Sleep(200);
}
}
int main()
{
thread task01(thread01);
thread task02(thread02);
task01.join();
task02.join();
for (int i = 0; i < 5; i++)
{
cout << "Main thread is working ！" << endl;
Sleep(200);
}
system("pause");
}
输出：
Thread 02 is working ！Thread 01 is working ！
Thread 01 is working ！
Thread 02 is working ！
Thread 01 is working ！
Thread 01 is working ！
Thread 02 is working ！
Thread 01 is working ！
Thread 02 is working ！
Thread 02 is working ！
Main thread is working ！
Main thread is working ！
Main thread is working ！
Main thread is working ！
Main thread is working ！
请按任意键继续. . .
两个子线程并行执行，join函数会阻塞主流程，所以子线程都执行完成之后才继续执行主线程。可以使用detach将子线程从主流程中分离，独立运行，不会阻塞主线程：
#include <iostream>
#include <thread>
#include <Windows.h>
using namespace std;
void thread01()
{
for (int i = 0; i < 5; i++)
{
cout << "Thread 01 is working ！" << endl;
Sleep(100);
}
}
void thread02()
{
for (int i = 0; i < 5; i++)
{
cout << "Thread 02 is working ！" << endl;
Sleep(200);
}
}
int main()
{
thread task01(thread01);
thread task02(thread02);
task01.detach();
task02.detach();
for (int i = 0; i < 5; i++)
{
cout << "Main thread is working ！" << endl;
Sleep(200);
}
system("pause");
}
输出：
Main thread is working ！
Thread 01 is working ！Thread 02 is working ！
Thread 01 is working ！
Thread 02 is working ！Main thread is working ！
Thread 01 is working ！
Thread 01 is working ！
Thread 02 is working ！Main thread is working ！
Thread 01 is working ！
Main thread is working ！Thread 02 is working ！
Main thread is working ！Thread 02 is working ！
请按任意键继续. . .
用detach的主线程和两个子线程并行执行。
在绑定的时候也可以同时给带参数的线程传入参数：
#include <iostream>
#include <thread>
#include <Windows.h>
using namespace std;
//定义带参数子线程
void thread01(int num)
{
for (int i = 0; i < num; i++)
{
cout << "Thread 01 is working ！" << endl;
Sleep(100);
}
}
void thread02(int num)
{
for (int i = 0; i < num; i++)
{
cout << "Thread 02 is working ！" << endl;
Sleep(200);
}
}
int main()
{
thread task01(thread01, 5); //带参数子线程
thread task02(thread02, 5);
task01.detach();
task02.detach();
for (int i = 0; i < 5; i++)
{
cout << "Main thread is working ！" << endl;
Sleep(200);
}
system("pause");
}
输出跟上例输出一样
多线程数据竞争
多个线程同时对同一变量进行操作的时候，如果不对变量做一些保护处理，有可能导致处理结果异常：
#include <iostream>
#include <thread>
#include <Windows.h>
using namespace std;
int totalNum = 100;
void thread01()
{
while (totalNum > 0)
{
cout << totalNum << endl;
totalNum--;
Sleep(100);
}
}
void thread02()
{
while (totalNum > 0)
{
cout << totalNum << endl;
totalNum--;
Sleep(100);
}
}
int main()
{
thread task01(thread01);
thread task02(thread02);
task01.detach();
task02.detach();
system("pause");
}
有两个问题，一是有很多变量被重复输出了，而有的变量没有被输出；二是正常情况下每个线程输出的数据后应该紧跟一个换行符，但这里大部分却是另一个线程的输出。
这是由于第一个线程对变量操作的过程中，第二个线程也对同一个变量进行各操作，导致第一个线程处理完后的输出有可能是线程二操作的结果。针对这种数据竞争的情况，可以使用线程互斥对象mutex保持数据同步。
mutex类的使用需要包含头文件mutex：
#include <iostream>
#include <thread>
#include <Windows.h>
#include <mutex>
using namespace std;
mutex mu; //线程互斥对象
int totalNum = 100;
void thread01()
{
while (totalNum > 0)
{
mu.lock(); //同步数据锁
cout << totalNum << endl;
totalNum--;
Sleep(100);
mu.unlock(); //解除锁定
}
}
void thread02()
{
while (totalNum > 0)
{
mu.lock();
cout << totalNum << endl;
totalNum--;
Sleep(100);
mu.unlock();
}
}
int main()
{
thread task01(thread01);
thread task02(thread02);
task01.detach();
task02.detach();
system("pause");
}
多线程中加入mutex互斥对象之后输出正常。
原文链接: https://www.cnblogs.com/Allen-rg/p/10744915.html
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