[C++知识库]c++11 std::async与std::future

范例一：

#include <iostream>
#include <string>
#include <thread>
#include <future>
using namespace std;

void aa()
{
	std::cout << "子线程ID = " << std::this_thread::get_id() << std::endl;
	while (1) {

	}
}

void run()
{
	//启动一个异步的线程，返回结果是一个函数模板，
	auto it = std::async(aa);
}
int main()
{
	//run();
	//用{}限制下std::async函数模板的作用域，注意看打印结果，由于aa函数里面有一个while循环
	//所以，在std::async还没有析构之前，只会打印出一个主线程ID，后续的不会打印，
	{
		auto it = std::async(aa);
		std::cout << "主线程ID = " << std::this_thread::get_id() << std::endl;
	}
	std::cout << "主线程ID = " << std::this_thread::get_id() << std::endl;
	std::cout << "主线程ID = " << std::this_thread::get_id() << std::endl;
	std::cout << "主线程ID = " << std::this_thread::get_id() << std::endl;
	std::cout << "主线程ID = " << std::this_thread::get_id() << std::endl;
	std::cout << "主线程ID = " << std::this_thread::get_id() << std::endl;
	std::cout << "主线程ID = " << std::this_thread::get_id() << std::endl;
	std::cout << "主线程ID = " << std::this_thread::get_id() << std::endl;
	std::cout << "主线程ID = " << std::this_thread::get_id() << std::endl;
	std::cout << "主线程ID = " << std::this_thread::get_id() << std::endl;
	std::cout << "主线程ID = " << std::this_thread::get_id() << std::endl;
	return 0;
}

范例二：

#include <iostream>
#include <string>
#include <thread>
#include <future>
using namespace std;
int run()
{
	std::cout << "子线程ID = " << std::this_thread::get_id() << std::endl;
	return 3;
}
int main()
{
	//启动一个异步线程
	auto it = std::async(run);
	std::cout << it.get() << std::endl; //获取函数返回结果
	return 0;
}

范例三：

#include <iostream>
#include <string>
#include <thread>
#include <future>
using namespace std;
int run()
{
	std::cout << "子线程ID = " << std::this_thread::get_id() << std::endl;
	return 3;
}
int main()
{
	//启动一个异步线程
	auto it = std::async(run);
	it.wait(); //等待线程返回
	return 0;
}

范例四：

#include <iostream>
#include <string>
#include <thread>
#include <future>
using namespace std;

int run()
{
	std::cout << "子线程ID = " << std::this_thread::get_id() << std::endl;
	return 3;
}
int main()
{
	//启动一个异步线程
	auto it = std::async(std::launch::deferred,run);
	std::cout << "主线程ID = " << std::this_thread::get_id() << std::endl;
	//如果没有调用wait成员函数或者get成员函数，则不会调用run函数，
	//如果调用了这些成员函数，者会调用run函数，但是不会创建新的线程
	it.wait(); //等待线程返回
	return 0;
}

std::async的参数还有其它，大家可以自行尝试。