C++多线程系列（C++11）（二）_what's the size of queque of threads in c++ on win-优快云博客

本文详细介绍C++中使用operator()作为线程入口的方法，包括无参与有参调用，参数传递方式（拷贝与引用），并演示如何获取线程ID及硬件支持的最大线程数。

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Date 2015/11/05 Ddd By WJB

上一次编写了一个最简单的多线程程序，这次介绍一种新的创建线程的方法和一些基本操作；

（上一篇文章连接：https://blog.youkuaiyun.com/wangjianbo09/article/details/80028515）

1，void operator()()：The first () is the name of the operator - it's the operator that is invoked when you use () on the object. The second () is for the parameters, of which there are none.

第一个()是操作符的名字, 当对象前面用()时，()的操作将被调用；第二个（）用于参数的传入，多用在多线程中。

实例:

class background_task
{
public:
 
    void operator()() const
    {
        do_something();
        do_something_else();
    }
};

background_task task;
task();

示例中传入参数为空。

2，void operator()()在多线程中的应用

class  fctor
{
public:
	void operator()()
	{
		for (int i =0;i<100;i++)
		{
			std::cout << "mythread:" << i << std::endl;
		}
	}

};

thread mythread1((fctor()));
mythread.join();

//需要传入参数，但参数是拷贝
class  fctor2
{
public:
	void operator()(std::string msg )
	{
		for (int i = 0; i < 100; i++)
		{
			cout << "fctor2"<<msg << endl;
		}
	}

};

thread mythread2((fctor2()),"I Love You!");
mythread2.join();

//需要传入参数，以引用的方式传入参数
class  fctor3
{
public:
	void operator()(std::string &msg)
	{
		cout << "fctor3 thread ID:" << std::this_thread::get_id() << endl; //输出当前线程ID
		cout << "fctor2" << msg << endl;
		msg = "I love you too;";
	}

};
std::string str = "I Love You!";
//thread mythread3((fctor3()),std::ref(str));//这种防暑传入参数会造成内存竞争，修改为move
thread mythread3((fctor3()), std::move(str));

3,多线程中的基本操作

获取当前线程：std::this_thread::get_id() ；
获取当点硬件支持的最大线程数：std::thread::hardware_concurrency()

4，全部代码（vs2015 win32控制台程序）main.cpp

#include <thread>
#include <iostream>
#include <string>
using namespace std;
void Function_1()
{
	printf("my name is multithread!");
}


class  fctor
{
public:
	void operator()()
	{
		for (int i =0;i<100;i++)
		{
			cout << "mythread:" << i << endl;
		}
	}

};
//需要传入参数，但参数是拷贝
class  fctor2
{
public:
	void operator()(std::string msg )
	{
		for (int i = 0; i < 100; i++)
		{
			cout << "fctor2"<<msg << endl;
		}
	}

};

//需要传入参数，以引用的方式传入参数
class  fctor3
{
public:
	void operator()(std::string &msg)
	{
		cout << "fctor3 thread ID:" << std::this_thread::get_id() << endl; //输出当前线程ID
		cout << "fctor2" << msg << endl;
		msg = "I love you too;";
	}

};

int main()
{
	fctor ftr;
	//thread mythread(ftr);           //两周调用方式等价
	//thread mythread1((fctor()));    //两周调用方式等价
	// 如果想传入参数如下
	//thread mythread2((fctor2()),"I Love You!");
	std::string str = "I Love You!";
	//thread mythread3((fctor3()),std::ref(str));//这种防暑传入参数会造成内存竞争，修改为move
	thread mythread3((fctor3()), std::move(str));
	mythread3.join();
	cout << "from main:" << str << endl;
	cout << "from main thread ID:" << std::this_thread::get_id() << endl; //输出当前线程ID

	cout << "hardware thread max：" << std::thread::hardware_concurrency() << endl; //输出当前线程ID

	//mythread.join();   //阻塞式
	//mythread1.join();
	//mythread2.join();				 
	// 非阻塞式
	 //mythread.detach();
	return 0;
}