Boost asio入门学习笔记

Timer1：使用一个同步计时器

#include <iostream>
#include "boost/asio.hpp"
int main()
{
boost::asio::io_context io;
boost::asio::steady_timer t(io, boost::asio::chrono::seconds(5));
t.wait();
std::cout << "Hello,world!" << std::endl;
return 0;
}

所谓的同步，就是指t.wait必须等待五秒才会向下执行。

Timer2：使用一个异步计时器

#include <iostream>
#include "boost/asio.hpp"
void print(const boost::system::error_code&)
{
std::cout << "Hello world!" << std::endl;
}
int main()
{
boost::asio::io_context io;
boost::asio::steady_timer t(io, boost::asio::chrono::seconds(5));
t.async_wait(&print);
std::cout << "Hehe!" << std::endl;
io.run();
return 0;
}

异步是指：上述程序并不会在t.async_wait(&print)处阻塞，而是继续运行，等到计时器计满5秒，才会调用print。上述程序的运行结果就是，先输出Hehe，再输出Hello world!。

Timer3：为handle绑定参数

#include <iostream>
#include "boost/asio.hpp"
#include "boost/bind.hpp"
void print(const boost::system::error_code&,boost::asio::steady_timer *t,int *count)
{
if (*count < 5)
{
std::cout << *count << std::endl;
++(*count);
t->expires_at(t->expiry() + boost::asio::chrono::seconds(1));//设置新的过期时间
t->async_wait(boost::bind(print, boost::asio::placeholders::error, t, count));//为print邦定参数，转换为函数对象
}
}
int main()
{
boost::asio::io_context io;
int count = 0;
boost::asio::steady_timer t(io, boost::asio::chrono::seconds(1));
t.async_wait(boost::bind(print,boost::asio::placeholders::error,&t,&count));
io.run();
std::cout << "Final count is " << count << std::endl;
return 0;
}

Timer4：使用一个成员函数作为handler

#include <iostream>
#include "boost/asio.hpp"
#include "boost/bind.hpp"
class printer
{
public:
printer(boost::asio::io_context& io)
:timer_(io, boost::asio::chrono::seconds(1)),
count_(0)
{
timer_.async_wait(boost::bind(&printer::print, this));
}
~printer()
{
std::cout << "Final count is " << count_ << std::endl;
}
void print()
{
if (count_ < 5)
{
std::cout << count_ << std::endl;
++count_;
timer_.expires_at(timer_.expiry() + boost::asio::chrono::seconds(1));
timer_.async_wait(boost::bind(&printer::print, this));
}
}
private:
boost::asio::steady_timer timer_;
int count_;
};
int main()
{
boost::asio::io_context io;
printer p(io);
io.run();
return 0;
}

与之前实例实现的功能一致，只不过更巧妙一些。the asio library provides a guarantee that callback handlers will only be called from threads that are currently calling io_context::run(). Consequently, calling io_context::run() from only one thread ensures that callback handlers cannot run concurrently.即，回调函数只能被一个线程调用，不能并行。

单线程有以下局限：

如果handle非常耗时，将会造成可怜的响应速度。
不能针对多核处理器进行扩展优化。

Timer5:多线程的同步Handlers

#include <iostream>
#include "boost/asio.hpp"
#include "boost/thread/thread.hpp"
#include "boost/bind.hpp"
class printer
{
public:
printer(boost::asio::io_context& io)
:strand_(io),
timer1_(io, boost::asio::chrono::seconds(1)),
timer2_(io,boost::asio::chrono::seconds(1)),
count_(0)
{
timer1_.async_wait(boost::asio::bind_executor(strand_, boost::bind(&printer::print1, this))); //邦定在同一个strand对象上的handler不能并发
timer2_.async_wait(boost::asio::bind_executor(strand_, boost::bind(&printer::print2, this)));
}
~printer()
{
std::cout << "Final count is " << count_ << std::endl;
}
void print1()
{
if(count_ < 10)
{
std::cout << "Timer 1: " << count_ << std::endl;
++count_;
timer1_.expires_at(timer1_.expiry() + boost::asio::chrono::seconds(1));
timer1_.async_wait(boost::asio::bind_executor(strand_,
boost::bind(&printer::print1, this)));
}
}
void print2()
{
if (count_ < 10)
{
std::cout << "Timer 2: " << count_ << std::endl;
++count_;
timer2_.expires_at(timer2_.expiry() + boost::asio::chrono::seconds(1));
timer2_.async_wait(boost::asio::bind_executor(strand_,
boost::bind(&printer::print2, this)));
}
}
private:
boost::asio::io_context::strand strand_;
boost::asio::steady_timer timer1_;
boost::asio::steady_timer timer2_;
int count_;
};
int main()
{
boost::asio::io_context io;
printer p(io);
boost::thread t(boost::bind(&boost::asio::io_context::run, &io));
io.run();
t.join();//等待子线程运行完毕
return 0;
}

daytime1：实现一个同步的TCP daytime客户端

#include <iostream>
#include<boost/array.hpp>
#include "boost/asio.hpp"
using boost::asio::ip::tcp;
int main(int argc,char * argv[])
{
try
{
boost::asio::io_context io_context; //All programs that use asio need to have at least one io_context object.
tcp::resolver resolver(io_context);
std::string host = "127.0.0.1";//specify the host
//resolver需要一个query对象,并将query转换为a list of endpoints
//host name,也就是IP地址
//the name of service,也就是端口...
tcp::resolver::query query(tcp::v4(), host, "13");
// tcp::resolver::query query(tcp::v4(),argv[1], "13");
tcp::resolver::results_type endpoints = resolver.resolve(query);
tcp::socket socket(io_context);
boost::asio::connect(socket, endpoints);
for (;;)
{
boost::array<char, 128>buf;
boost::system::error_code error;
size_t len = socket.read_some(boost::asio::buffer(buf), error);
if (error == boost::asio::error::eof)
{
break;//连接关闭
}
else if (error)
{
throw boost::system::system_error(error);
}
std::cout.write(buf.data(), len);
}
}
catch (const std::exception& e)
{
std::cerr << e.what() << std::endl;
}
return 0;
}

daytime2:实现一个同步的TCP daytime 服务端

#include <ctime>
#include <iostream>
#include <string>
#include <boost/asio.hpp>
using boost::asio::ip::tcp;
std::string make_daytime_string()
{
using namespace std;
time_t now = time(0);
return ctime(&now);
}
int main()
{
try
{
boost::asio::io_context io_context;
tcp::acceptor acceptor(io_context, tcp::endpoint(tcp::v4(), 13));
for (;;)
{
tcp::socket socket(io_context);
acceptor.accept(socket);
std::string message = make_daytime_string();
boost::system::error_code igored_error;
boost::asio::write(socket, boost::asio::buffer(message), igored_error);
}
}
catch (const std::exception& e)
{
std::cerr << e.what() << std::endl;
}
}

daytime3:一个异步tcp daytime的服务端

#include <ctime>
#include <iostream>
#include <string>
#include <boost/asio.hpp>
#include <boost/enable_shared_from_this.hpp>
#include <boost/bind.hpp>
using boost::asio::ip::tcp;
std::string make_daytime_string()
{
using namespace std;
time_t now = time(0);
return ctime(&now);
}
class tcp_connection :public boost::enable_shared_from_this<tcp_connection>
{
public:
typedef boost::shared_ptr<tcp_connection> pointer;
static pointer create(boost::asio::io_context&io_context)
{
return pointer(new tcp_connection(io_context));
}
tcp::socket & socket()
{
return socket_;
}
void start()
{
message_ = make_daytime_string();
boost::asio::async_write(socket_, boost::asio::buffer(message_), boost::bind(&tcp_connection::handle_write, shared_from_this(),
boost::asio::placeholders::error, boost::asio::placeholders::bytes_transferred));
}
private:
tcp_connection(boost::asio::io_context&io_context)
:socket_(io_context)
{
}
void handle_write(const boost::system::error_code, size_t)
{
}
tcp::socket socket_;
std::string message_;
};
class tcp_server
{
public:
tcp_server(boost::asio::io_context&io_context)
:acceptor_(io_context, tcp::endpoint(tcp::v4(), 13))
{
start_accept();
}
private:
void start_accept()
{
tcp_connection::pointer new_connection = tcp_connection::create(acceptor_.get_executor().context());
acceptor_.async_accept(new_connection->socket(), boost::bind(&tcp_server::handle_accept, this, new_connection, boost::asio::placeholders::error));
//此处不阻塞，直接返回，当有连接到达时，调用handle_accept
}
void handle_accept(tcp_connection::pointer new_connection,
const boost::system::error_code& error)
{
if (!error)
{
new_connection->start();
}
start_accept();
}
tcp::acceptor acceptor_;
};
int main()
{
try
{
boost::asio::io_context io_context;
tcp_server server(io_context);
io_context.run();
}
catch (const std::exception& e)
{
std::cerr << e.what() << std::endl;
}
}

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