boost asio 学习(六) 定时器

http://www.gamedev.net/blog/950/entry-2249317-a-guide-to-getting-
started-with-boostasio?pg=7

6 定时器

boost::asio 提供了一个 deadline_timer class来提供同步与异步的接口。
BOOST文档提供了一组优秀示例。
第一个例子，将创建一个间隔5秒的定时器。

#include <boost/asio.hpp>
#include <boost/shared_ptr.hpp>
#include <boost/thread.hpp>
#include <boost/thread/mutex.hpp>
#include <boost/bind.hpp>
#include <iostream>

boost::mutex global_stream_lock;

void WorkerThread(boost::shared_ptr< boost::asio::io_service > 

io_service)
{
	global_stream_lock.lock();
	std::cout << "[" << boost::this_thread::get_id()
		<< "] Thread Start" << std::endl;
	global_stream_lock.unlock();

	while (true)
	{
		try
		{
			boost::system::error_code ec;
			io_service->run(ec);
			if (ec)
			{
				global_stream_lock.lock();
				std::cout << "[" << 

boost::this_thread::get_id()
					<< "] Error: " << ec << 

std::endl;
				global_stream_lock.unlock();
			}
			break;
		}
		catch (std::exception & ex)
		{
			global_stream_lock.lock();
			std::cout << "[" << 

boost::this_thread::get_id()
				<< "] Exception: " << ex.what() << 

std::endl;
			global_stream_lock.unlock();
		}
	}

	global_stream_lock.lock();
	std::cout << "[" << boost::this_thread::get_id()
		<< "] Thread Finish" << std::endl;
	global_stream_lock.unlock();
}

void TimerHandler(const boost::system::error_code & error)
{
	if (error)
	{
		global_stream_lock.lock();
		std::cout << "[" << boost::this_thread::get_id()
			<< "] Error: " << error << std::endl;
		global_stream_lock.unlock();
	}
	else
	{
		global_stream_lock.lock();
		std::cout << "[" << boost::this_thread::get_id()
			<< "] TimerHandler " << std::endl;
		global_stream_lock.unlock();
	}
}

int main(int argc, char * argv[])
{
	boost::shared_ptr< boost::asio::io_service > io_service(
		new boost::asio::io_service
		);
	boost::shared_ptr< boost::asio::io_service::work > work(
		new boost::asio::io_service::work(*io_service)
		);

	global_stream_lock.lock();
	std::cout << "[" << boost::this_thread::get_id()
		<< "] Press [return] to exit." << std::endl;
	global_stream_lock.unlock();

	boost::thread_group worker_threads;
	for (int x = 0; x < 2; ++x)
	{
		worker_threads.create_thread(boost::bind

(&WorkerThread, io_service));
	}

	boost::asio::deadline_timer timer(*io_service);
	timer.expires_from_now(boost::posix_time::seconds(5));
	timer.async_wait(TimerHandler);

	std::cin.get();

	io_service->stop();

	worker_threads.join_all();

	return 0;
}

　　

如果我们想创建一个可冲用的定时器.我们将定时器对象设置为全局，但是可能
导致共享对象不是线程安全的。boost::bind能解决这个问题。使用定时器对象
的shared_ptr指针，我们能使用bind并且传递定时器到指定的handler，保持定
时器可重用。

#include <boost/asio.hpp>
#include <boost/shared_ptr.hpp>
#include <boost/thread.hpp>
#include <boost/thread/mutex.hpp>
#include <boost/bind.hpp>
#include <iostream>

boost::mutex global_stream_lock;

void WorkerThread(boost::shared_ptr< boost::asio::io_service > 

io_service)
{
	global_stream_lock.lock();
	std::cout << "[" << boost::this_thread::get_id()
		<< "] Thread Start" << std::endl;
	global_stream_lock.unlock();

	while (true)
	{
		try
		{
			boost::system::error_code ec;
			io_service->run(ec);
			if (ec)
			{
				global_stream_lock.lock();
				std::cout << "[" << 

boost::this_thread::get_id()
					<< "] Error: " << ec << 

std::endl;
				global_stream_lock.unlock();
			}
			break;
		}
		catch (std::exception & ex)
		{
			global_stream_lock.lock();
			std::cout << "[" << 

boost::this_thread::get_id()
				<< "] Exception: " << ex.what() << 

std::endl;
			global_stream_lock.unlock();
		}
	}

	global_stream_lock.lock();
	std::cout << "[" << boost::this_thread::get_id()
		<< "] Thread Finish" << std::endl;
	global_stream_lock.unlock();
}

void TimerHandler(
	const boost::system::error_code & error,
	boost::shared_ptr< boost::asio::deadline_timer > timer
	)
{
	if (error)
	{
		global_stream_lock.lock();
		std::cout << "[" << boost::this_thread::get_id()
			<< "] Error: " << error << std::endl;
		global_stream_lock.unlock();
	}
	else
	{
		global_stream_lock.lock();
		std::cout << "[" << boost::this_thread::get_id()
			<< "] TimerHandler " << std::endl;
		global_stream_lock.unlock();

		timer->expires_from_now(boost::posix_time::seconds

(5));
		timer->async_wait(boost::bind(&TimerHandler, _1, 

timer));
	}
}

int main(int argc, char * argv[])
{
	boost::shared_ptr< boost::asio::io_service > io_service(
		new boost::asio::io_service
		);
	boost::shared_ptr< boost::asio::io_service::work > work(
		new boost::asio::io_service::work(*io_service)
		);

	global_stream_lock.lock();
	std::cout << "[" << boost::this_thread::get_id()
		<< "] Press [return] to exit." << std::endl;
	global_stream_lock.unlock();

	boost::thread_group worker_threads;
	for (int x = 0; x < 2; ++x)
	{
		worker_threads.create_thread(boost::bind

(&WorkerThread, io_service));
	}

	boost::shared_ptr< boost::asio::deadline_timer > timer(
		new boost::asio::deadline_timer(*io_service)
		);
	timer->expires_from_now(boost::posix_time::seconds(5));
	timer->async_wait(boost::bind(&TimerHandler, _1, timer));

	std::cin.get();

	io_service->stop();

	worker_threads.join_all();

	return 0;
}

　　

使用bind可以做许多有趣的事情，_1参数是一个占位符。因为TimerHandler 函
数需要一个参数用于回调，我们需要引用这个bind调用。_1意味着第一个参数，
我们稍后提供。

运行上面例子，我们将获得一个每五秒激活一次的定时器。
如果想保证定时器不和work处理器同时运行，我们可以使用strand。
代码如下

#include <boost/asio.hpp>
#include <boost/shared_ptr.hpp>
#include <boost/thread.hpp>
#include <boost/thread/mutex.hpp>
#include <boost/bind.hpp>
#include <iostream>

boost::mutex global_stream_lock;

void WorkerThread(boost::shared_ptr< boost::asio::io_service > io_service)
{
	global_stream_lock.lock();
	std::cout << "[" << boost::this_thread::get_id()
		<< "] Thread Start" << std::endl;
	global_stream_lock.unlock();

	while (true)
	{
		try
		{
			boost::system::error_code ec;
			io_service->run(ec);
			if (ec)
			{
				global_stream_lock.lock();
				std::cout << "[" << boost::this_thread::get_id()
					<< "] Error: " << ec << std::endl;
				global_stream_lock.unlock();
			}
			break;
		}
		catch (std::exception & ex)
		{
			global_stream_lock.lock();
			std::cout << "[" << boost::this_thread::get_id()
				<< "] Exception: " << ex.what() << std::endl;
			global_stream_lock.unlock();
		}
	}

	global_stream_lock.lock();
	std::cout << "[" << boost::this_thread::get_id()
		<< "] Thread Finish" << std::endl;
	global_stream_lock.unlock();
}

void TimerHandler(
	const boost::system::error_code & error,
	boost::shared_ptr< boost::asio::deadline_timer > timer,
	boost::shared_ptr< boost::asio::io_service::strand > strand
	)
{
	if (error)
	{
		global_stream_lock.lock();
		std::cout << "[" << boost::this_thread::get_id()
			<< "] Error: " << error << std::endl;
		global_stream_lock.unlock();
	}
	else
	{
		std::cout << "[" << boost::this_thread::get_id()
			<< "] TimerHandler " << std::endl;

		timer->expires_from_now(boost::posix_time::seconds(1));
		timer->async_wait(
			strand->wrap(boost::bind(&TimerHandler, _1, timer, strand))
			);
	}
}

void PrintNum(int x)
{
	std::cout << "[" << boost::this_thread::get_id()
		<< "] x: " << x << std::endl;
	boost::this_thread::sleep(boost::posix_time::milliseconds(1000));
}

int main(int argc, char * argv[])
{
	boost::shared_ptr< boost::asio::io_service > io_service(
		new boost::asio::io_service
		);
	boost::shared_ptr< boost::asio::io_service::work > work(
		new boost::asio::io_service::work(*io_service)
		);
	boost::shared_ptr< boost::asio::io_service::strand > strand(
		new boost::asio::io_service::strand(*io_service)
		);

	global_stream_lock.lock();
	std::cout << "[" << boost::this_thread::get_id()
		<< "] Press [return] to exit." << std::endl;
	global_stream_lock.unlock();

	boost::thread_group worker_threads;
	for (int x = 0; x < 2; ++x)
	{
		worker_threads.create_thread(boost::bind(&WorkerThread, io_service));
	}

	boost::this_thread::sleep(boost::posix_time::seconds(1));

	strand->post(boost::bind(&PrintNum, 1));
	strand->post(boost::bind(&PrintNum, 2));
	strand->post(boost::bind(&PrintNum, 3));
	strand->post(boost::bind(&PrintNum, 4));
	strand->post(boost::bind(&PrintNum, 5));

	boost::shared_ptr< boost::asio::deadline_timer > timer(
		new boost::asio::deadline_timer(*io_service)
		);
	timer->expires_from_now(boost::posix_time::seconds(1));
	timer->async_wait(
		strand->wrap(boost::bind(&TimerHandler, _1, timer, strand))
		);

	std::cin.get();

	io_service->stop();

	worker_threads.join_all();

	return 0;
}

　　

我们需要使用strand封装定时器处理器，strand能确保工作对象先运行而后定时器线程后运行。

本章节我们学习如何使用bind strand shard_ptr来获取灵活性和实现功能。在后面的网络系统中我们将使用这些组件。