Thread使用

1.join作用

1.1 不加join

#include <iostream>
#include <thread>
#include <mutex>
#include <Windows.h>

using namespace std;

int g_num = 0;
mutex g_mutex;

void thread1()
{
	g_num = 50;
	for (int i = 0; i < 10; ++i)
		cout << "thread1:" << g_num << endl;
}

void thread2()
{
	g_num = 100;
	for (int j = 0; j < 10; ++j)
		cout << "thread2:" << g_num << endl;
}

int main(int argc, char* argv[])
{
	thread t1(thread1);
	thread t2(thread2);

	// Sleep(10000);

	system("pause");
	return 0;
}

补充说明：关闭窗口时，出现问题，是因为主线程比子线程先退出了，而子线程还没有结束，导致了子线程还没有析构的问题。

1.2 加join()

#include <iostream>
#include <thread>
#include <mutex>
#include <Windows.h>

using namespace std;

int g_num = 0;
mutex g_mutex;

void thread1()
{
	g_num = 50;
	for (int i = 0; i < 10; ++i)
		cout << "thread1:" << g_num << endl;
}

void thread2()
{
	g_num = 100;
	for (int j = 0; j < 10; ++j)
		cout << "thread2:" << g_num << endl;
}

int main(int argc, char* argv[])
{
	thread t1(thread1);
	thread t2(thread2);
	t1.join();
	t2.join();


	system("pause");
	return 0;
}

补充说明：关闭窗口，正常退出。join()会阻塞主线程，就是说t1和t2完成后，才会回到主线程调用system("pause"); 程序继续往后执行。

2.mutex作用

2种添加互斥的方法都可以实现对数据的保护，保证一个线程里的数据不会收到另一个线程的影响。

mutex::lock和mutex::unlock之间的数据进行保护；而lock_guard<mutex>对析构前所在作用域内的数据进行保护。

#include <iostream>
#include <thread>
#include <mutex>
#include <Windows.h>

using namespace std;

int g_num = 0;
mutex g_mutex;

void thread1()
{
	g_mutex.lock();
	g_num = 50;
	for (int i = 0; i < 10; ++i)
		cout << "thread1:" << g_num << endl;
	g_mutex.unlock();
}

void thread2()
{
    //用这种方式更安全
	lock_guard<mutex>lg(g_mutex);   
	g_num = 100;
	for (int j = 0; j < 10; ++j)
		cout << "thread2:" << g_num << endl;
}

int main(int argc, char* argv[])
{
	thread t1(thread1);
	thread t2(thread2);
	t1.join();
	t2.join();

	Sleep(10000);

	system("pause");
	return 0;
}