boost::asio阻塞等待与异步等待

阻塞等待：这里会等待3秒而后才进行输出。

#include <iostream>
#include <boost/asio.hpp>
#include <boost/date_time/posix_time/posix_time.hpp>

int main(void)
{
	boost::asio::io_service io;
	boost::asio::deadline_timer timer(io, boost::posix_time::seconds(3));
	timer.wait();
	std::cout << "this is blocking wait" << std::endl;

	system("pause");
	return 0;
}

异步等待：须要一个回调函数，在等待这个print回调函数的时候程序会继续往下执行到io.run为止，3秒事后才会执行回调函数。若是在3秒内程序尚未执行到io.run（如加上sleep(5)），那么5秒后才会执行print，也就是说在执行io.run以前print是不会执行的。

#include <iostream>
#include <boost/asio.hpp>
#include <boost/date_time/posix_time/posix_time.hpp>

void print(const boost::system::error_code & e)
{
	std::cout << "hello, world" << std::endl;
}

int main(void)
{
	boost::asio::io_service io;
	boost::asio::deadline_timer timer(io, boost::posix_time::seconds(3));
	timer.async_wait(&print);
	std::cout << "this is asynchronous wait" << std::endl;
        // sleep(5);
	io.run();

	system("pause");
	return 0;
}

// 开始timer的异步等待时间是1秒，1秒后会执行print回调函数，在这个函数里会进行5次递归调用。因为timer的

// 终止时间是1秒已经到期了因此在递归的过程当中不会再每秒执行一次的，为了实现每秒输出的效果咱们须要为这个

// timer延迟终止时间，expires_at就是其这个做用。固然expires_at必须在async_wait以前执行，不然是没有效果的。

#include <iostream>
#include <boost/asio.hpp>
#include <boost/date_time/posix_time/posix_time.hpp>
#include <boost/bind.hpp>
#include <windows.h>

unsigned int start_t, end_t;
void print(const boost::system::error_code& e, boost::asio::deadline_timer* timer, int* count)
{
	if (*count < 5)
	{
		std::cout << "count: " << *count << std::endl;
		end_t = ::GetTickCount();
		std::cout << "elapse time:" << end_t-start_t << std::endl;
		++(*count);
                //timer->expires_from_now(boost::posix_time::seconds(1));
		timer->expires_at(timer->expires_at() + boost::posix_time::seconds(1));
		timer->async_wait(boost::bind(print, boost::asio::placeholders::error, timer, count));
	}
}

int main()
{
	int count = 0;
	boost::asio::io_service io;
	boost::asio::deadline_timer timer(io, boost::posix_time::seconds(1));
	timer.async_wait(boost::bind(print, boost::asio::placeholders::error, &timer, &count));
	start_t = ::GetTickCount();
	io.run();
	std::cout << "run end" << std::endl;

	system("pause");
	return 0;
}

// 下面是类成员函数回调的形式

#include <iostream>
#include <boost/asio.hpp>
#include <boost/date_time/posix_time/posix_time.hpp>
#include <boost/bind.hpp>

class Printer
{
public:
	Printer(boost::asio::io_service& io)
		: count_(0), timer_(io, boost::posix_time::seconds(1))
	{
		timer_.async_wait(boost::bind(&Printer::print, this));
	}

	~Printer()
	{
	}

	void print()
	{
		if (count_ < 5)
		{
			std::cout << "count: " << count_ << std::endl;
			++count_;
			timer_.expires_from_now(boost::posix_time::seconds(1));
			timer_.async_wait(boost::bind(&Printer::print, this));
		}
	}

private:
	int count_;
	boost::asio::deadline_timer timer_;
};

int main()
{
	boost::asio::io_service io;
	Printer printer(io);
	io.run();

	system("pause");
	return 0;
}