BOOST.ASIO源码剖析(三) ---- 流程分析

2018/04/11 14:40
阅读数 1.2K

 常见流程分析之一(Tcp异步连接)

 

我们用一个简单的demo分析Tcp异步连接的流程:

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1 #include <iostream>
 2 #include <boost/asio.hpp>
 3 
 4 // 异步连接回调函数
 5 void on_connect(boost::system::error_code ec)
 6 {
 7     if (ec)  // 连接失败, 输出错误码
 8         std::cout << "async connect error:" << ec.message() << std::endl;
 9     else  // 连接成功
10         std::cout << "async connect ok!" << std::endl;
11 }
12 
13 int main()
14 {
15     boost::asio::io_service ios;  // 创建io_service对象
16     boost::asio::ip::tcp::endpoint addr(
17         boost::asio::ip::address::from_string("127.0.0.1"), 12345);  // server端地址
18     boost::asio::ip::tcp::socket conn_socket(ios);  // 创建tcp协议的socket对象
19     conn_socket.async_connect(addr, &on_connect);  // 发起异步连接请求
20     ios.run();  // 调用io_service::run, 等待异步操作结果
21 
22     std::cin.get();
23     return 0;
24 }

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这段代码中的异步连接请求在asio源码中的序列图如下:

 

      其中,basic_socket是个模板类,tcp协议中的socket的定义如下:
            typedef basic_socket<tcp> socket;


      reactor的定义如下:
      #if defined(BOOST_ASIO_WINDOWS_RUNTIME)
            typedef class null_reactor reactor;
      #elif defined(BOOST_ASIO_HAS_IOCP)
            typedef class select_reactor reactor;
      #elif defined(BOOST_ASIO_HAS_EPOLL)
            typedef class epoll_reactor reactor;
      #elif defined(BOOST_ASIO_HAS_KQUEUE)
            typedef class kqueue_reactor reactor;
      #elif defined(BOOST_ASIO_HAS_DEV_POLL)
            typedef class dev_poll_reactor reactor;
      #else
            typedef class select_reactor reactor;
      #endif

      在这个序列图中最值得注意的一点是:在windows平台下,异步连接请求不是由Iocp处理的,而是由select模型处理的,这是与异步读写数据最大的不同之处。

 


* 常见流程分析之二(Tcp异步接受连接)

 

我们用一个简单的demo分析Tcp异步连接的流程:

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1 #include <iostream>
 2 #include <boost/asio.hpp>
 3 #include <boost/bind.hpp>
 4 
 5 // 异步连接回调函数
 6 void on_accept(boost::system::error_code ec, boost::asio::ip::tcp::socket * socket_ptr)
 7 {
 8     if (ec)  // 连接失败, 输出错误码
 9         std::cout << "async accept error:" << ec.message() << std::endl;
10     else  // 连接成功
11         std::cout << "async accept from (" << socket_ptr->remote_endpoint() << ")" << std::endl;
12 
13     // 断开连接, 释放资源.
14     socket_ptr->close(), delete socket_ptr;
15 }
16 
17 int main()
18 {
19     boost::asio::io_service ios;  // 创建io_service对象
20     boost::asio::ip::tcp::endpoint addr(
21         boost::asio::ip::address::from_string("0.0.0.0"), 12345);  // server端地址
22     boost::asio::ip::tcp::acceptor acceptor(ios, addr, false);  // 创建acceptor对象
23     boost::asio::ip::tcp::socket * socket_ptr = new boost::asio::ip::tcp::socket(ios);
24     acceptor.async_accept(*socket_ptr
25         , boost::bind(&on_accept, boost::asio::placeholders::error, socket_ptr));  // 调用异步accept请求
26     ios.run();  // 调用io_service::run, 等待异步操作结果
27 
28     std::cin.get();
29     return 0;
30 }

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这段代码中的异步连接请求在asio源码中的序列图如下:

 


* 常见流程分析之三(Tcp异步读写数据)

 

我们依然以上一节的例子为基础,扩展一个简单的demo分析Tcp异步读写数据的流程:

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1 #include <iostream>
 2 #include <boost/asio.hpp>
 3 #include <boost/bind.hpp>
 4 #include <boost/shared_ptr.hpp>
 5 #include <boost/array.hpp>
 6 
 7 typedef boost::shared_ptr<boost::asio::ip::tcp::socket> socket_ptr_t;
 8 typedef boost::array<char, 128> buffer_t;
 9 typedef boost::shared_ptr<buffer_t> buffer_ptr_t;
10 
11 // 异步读数据回调函数
12 void on_read(boost::system::error_code ec
13     , std::size_t len, socket_ptr_t socket_ptr, buffer_ptr_t buffer_ptr)
14 {
15     if (ec)
16         std::cout << "async write error:" << ec.message() << std::endl;
17     else
18     {
19         std::cout << "async read size:" << len;
20         std::cout << " info:" << std::string((char*)buffer_ptr->begin(), len) << std::endl;
21 
22         // auto release socket and buffer.
23     }
24 }
25 
26 // 异步写数据回调函数
27 void on_write(boost::system::error_code ec
28     , std::size_t len, socket_ptr_t socket_ptr, buffer_ptr_t buffer_ptr)
29 {
30     if (ec)
31         std::cout << "async write error:" << ec.message() << std::endl;
32     else
33     {
34         std::cout << "async write size:" << len << std::endl;
35         socket_ptr->async_read_some(boost::asio::buffer(buffer_ptr.get(), buffer_t::size())
36             , boost::bind(&on_read, boost::asio::placeholders::error, boost::asio::placeholders::bytes_transferred
37                 , socket_ptr, buffer_ptr));
38     }
39 }
40 
41 // 异步连接回调函数
42 void on_accept(boost::system::error_code ec, socket_ptr_t socket_ptr)
43 {
44     if (ec)  // 连接失败, 输出错误码
45     {
46         std::cout << "async accept error:" << ec.message() << std::endl;
47     }
48     else  // 连接成功
49     {
50         std::cout << "async accept from (" << socket_ptr->remote_endpoint() << ")" << std::endl;
51         buffer_ptr_t buffer_ptr(new buffer_t);
52         strcpy_s((char*)buffer_ptr->begin(), buffer_t::size(), "abcdefg");
53         socket_ptr->async_write_some(boost::asio::buffer(buffer_ptr.get(), strlen((char*)buffer_ptr->begin()))
54             , boost::bind(&on_write, boost::asio::placeholders::error, boost::asio::placeholders::bytes_transferred
55                 , socket_ptr, buffer_ptr));
56     }
57 }
58 
59 int main()
60 {
61     boost::asio::io_service ios;  // 创建io_service对象
62     boost::asio::ip::tcp::endpoint addr(
63         boost::asio::ip::address::from_string("0.0.0.0"), 12345);  // server端地址
64     boost::asio::ip::tcp::acceptor acceptor(ios, addr, false);  // 创建acceptor对象
65     socket_ptr_t socket_ptr(new boost::asio::ip::tcp::socket(ios));
66     acceptor.async_accept(*socket_ptr
67         , boost::bind(&on_accept, boost::asio::placeholders::error, socket_ptr));  // 调用异步accept请求
68     ios.run();  // 调用io_service::run, 等待异步操作结果
69 
70     std::cout << "press enter key...";
71     std::cin.get();
72     return 0;
73 }

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这段代码中的异步连接请求在asio源码中的序列图如下:

 


* 常见流程分析之四(Tcp强制关闭连接)

我们依然以上一节的例子为基础,扩展一个简单的demo分析Tcp强制关闭连接的流程:

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1 #include <iostream>
 2 #include <boost/asio.hpp>
 3 #include <boost/bind.hpp>
 4 #include <boost/shared_ptr.hpp>
 5 #include <boost/array.hpp>
 6 
 7 typedef boost::shared_ptr<boost::asio::ip::tcp::socket> socket_ptr_t;
 8 typedef boost::array<char, 128> buffer_t;
 9 typedef boost::shared_ptr<buffer_t> buffer_ptr_t;
10 
11 // 异步读数据回调函数
12 void on_read(boost::system::error_code ec
13     , std::size_t len, socket_ptr_t socket_ptr, buffer_ptr_t buffer_ptr)
14 {
15     if (ec)  // 连接失败, 输出错误码
16     {
17         std::cout << "async read error:" << ec.message() << std::endl;
18     }
19 }
20 
21 // 异步写数据回调函数
22 void on_write(boost::system::error_code ec
23     , std::size_t len, socket_ptr_t socket_ptr, buffer_ptr_t buffer_ptr)
24 {
25     if (ec)  // 连接失败, 输出错误码
26     {
27         std::cout << "async write error:" << ec.message() << std::endl;
28     }
29 }
30 
31 // 异步连接回调函数
32 void on_accept(boost::system::error_code ec, socket_ptr_t socket_ptr)
33 {
34     if (ec)  // 连接失败, 输出错误码
35     {
36         std::cout << "async accept error:" << ec.message() << std::endl;
37     }
38     else  // 连接成功
39     {
40         std::cout << "async accept from (" << socket_ptr->remote_endpoint() << ")" << std::endl;
41 
42         {
43             buffer_ptr_t buffer_ptr(new buffer_t);
44             strcpy_s((char*)buffer_ptr->begin(), buffer_t::size(), "abcdefg");
45             socket_ptr->async_write_some(boost::asio::buffer(buffer_ptr.get(), strlen((char*)buffer_ptr->begin()))
46                 , boost::bind(&on_write, boost::asio::placeholders::error, boost::asio::placeholders::bytes_transferred
47                 , socket_ptr, buffer_ptr));
48         }
49 
50         {
51             buffer_ptr_t buffer_ptr(new buffer_t);
52             socket_ptr->async_read_some(boost::asio::buffer(buffer_ptr.get(), buffer_t::size())
53                 , boost::bind(&on_read, boost::asio::placeholders::error, boost::asio::placeholders::bytes_transferred
54                 , socket_ptr, buffer_ptr));
55         }
56 
57         /// 强制关闭连接
58         socket_ptr->close(ec);
59         if (ec)
60             std::cout << "close error:" << ec.message() << std::endl;
61     }
62 }
63 
64 int main()
65 {
66     boost::asio::io_service ios;  // 创建io_service对象
67     boost::asio::ip::tcp::endpoint addr(
68         boost::asio::ip::address::from_string("0.0.0.0"), 12345);  // server端地址
69     boost::asio::ip::tcp::acceptor acceptor(ios, addr, false);  // 创建acceptor对象
70     socket_ptr_t socket_ptr(new boost::asio::ip::tcp::socket(ios));
71     acceptor.async_accept(*socket_ptr
72         , boost::bind(&on_accept, boost::asio::placeholders::error, socket_ptr));  // 调用异步accept请求
73     socket_ptr.reset();
74     ios.run();  // 调用io_service::run, 等待异步操作结果
75 
76     std::cout << "press enter key...";
77     std::cin.get();
78     return 0;
79 }

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这个例子中,接受到客户端的连接后,立即发起异步读请求和异步写请求,然后立即强制关闭socket。

其中,强制关闭socket的请求在asio源码中的序列图如下:

 

* 常见流程分析之五(Tcp优雅地关闭连接)

我们依然以第三节的例子为基础,扩展一个简单的demo分析Tcp优雅地关闭连接的流程:

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1 #include <iostream>
 2 #include <boost/asio.hpp>
 3 #include <boost/bind.hpp>
 4 #include <boost/shared_ptr.hpp>
 5 #include <boost/array.hpp>
 6 
 7 typedef boost::shared_ptr<boost::asio::ip::tcp::socket> socket_ptr_t;
 8 typedef boost::array<char, 32> buffer_t;
 9 typedef boost::shared_ptr<buffer_t> buffer_ptr_t;
10 
11 
12 // 异步读数据回调函数
13 void on_read(boost::system::error_code ec
14     , std::size_t len, socket_ptr_t socket_ptr, buffer_ptr_t buffer_ptr)
15 {
16     static int si = 0;
17     if (ec)  // 连接失败, 输出错误码
18     {
19         std::cout << "async read(" << si++ << ") error:" << ec.message() << std::endl;
20         socket_ptr->shutdown(boost::asio::socket_base::shutdown_receive, ec);
21         socket_ptr->close(ec);
22         if (ec)
23             std::cout << "close error:" << ec.message() << std::endl;
24     }
25     else
26     {
27         std::cout << "read(" << si++ << ") len:" << len << std::endl;
28 
29         socket_ptr->async_read_some(boost::asio::buffer(buffer_ptr.get(), buffer_t::size())
30             , boost::bind(&on_read, boost::asio::placeholders::error, boost::asio::placeholders::bytes_transferred
31             , socket_ptr, buffer_ptr));
32     }
33 }
34 
35 // 异步写数据回调函数
36 void on_write(boost::system::error_code ec
37     , std::size_t len, socket_ptr_t socket_ptr, buffer_ptr_t buffer_ptr)
38 {
39     if (ec)  // 连接失败, 输出错误码
40     {
41         std::cout << "async write error:" << ec.message() << std::endl;
42     }
43     else
44     {
45         /// 优雅地关闭连接
46         socket_ptr->shutdown(boost::asio::ip::tcp::socket::shutdown_send, ec);
47         if (ec)
48             std::cout << "shutdown send error:" << ec.message() << std::endl;
49     }
50 }
51 
52 // 异步连接回调函数
53 void on_accept(boost::system::error_code ec, socket_ptr_t socket_ptr)
54 {
55     if (ec)  // 连接失败, 输出错误码
56     {
57         std::cout << "async accept error:" << ec.message() << std::endl;
58     }
59     else  // 连接成功
60     {
61         std::cout << "async accept from (" << socket_ptr->remote_endpoint() << ")" << std::endl;
62 
63         {
64             buffer_ptr_t buffer_ptr(new buffer_t);
65             socket_ptr->async_read_some(boost::asio::buffer(buffer_ptr.get(), buffer_t::size())
66                 , boost::bind(&on_read, boost::asio::placeholders::error, boost::asio::placeholders::bytes_transferred
67                 , socket_ptr, buffer_ptr));
68         }
69 
70         {
71             buffer_ptr_t buffer_ptr(new buffer_t);
72             strcpy_s((char*)buffer_ptr->begin(), buffer_t::size(), "abcdefg");
73             socket_ptr->async_write_some(boost::asio::buffer(buffer_ptr.get(), strlen((char*)buffer_ptr->begin()))
74                 , boost::bind(&on_write, boost::asio::placeholders::error, boost::asio::placeholders::bytes_transferred
75                 , socket_ptr, buffer_ptr));
76         }
77     }
78 }
79 
80 int main()
81 { 
82     boost::asio::io_service ios;  // 创建io_service对象
83     boost::asio::ip::tcp::endpoint addr(
84         boost::asio::ip::address::from_string("0.0.0.0"), 12345);  // server端地址
85     boost::asio::ip::tcp::acceptor acceptor(ios, addr, false);  // 创建acceptor对象
86     socket_ptr_t socket_ptr(new boost::asio::ip::tcp::socket(ios));
87     acceptor.async_accept(*socket_ptr
88         , boost::bind(&on_accept, boost::asio::placeholders::error, socket_ptr));  // 调用异步accept请求
89     socket_ptr.reset();
90     ios.run();  // 调用io_service::run, 等待异步操作结果
91 
92     std::cout << "press enter key...";
93     std::cin.get();
94     return 0;
95 }

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      在这个例子中,接收到客户端的连接并向客户端发送数据以后,先关闭socket的发送通道,然后等待socket接收缓冲区中的数据全部read出来以后,再关闭socket的接收通道。此时,socket的接收和发送通道均以关闭,任何进程都无法使用此socket收发数据,但其所占用的系统资源并未释放,底层发送缓冲区中的数据也不保证已全部发出,需要在此之后执行close操作以便释放系统资源。
      若在释放系统资源前希望底层发送缓冲区中的数据依然可以发出,则需在socket的linger属性中设置一个等待时间,以便有时间等待发送缓冲区中的数据发送完毕。但linger中的值绝对不是越大越好,这是因为其原理是操作系统帮忙保留socket的资源以等待其发送缓冲区中的数据发送完毕,如果远端socket的一直未能接收数据便会导致本地socket一直等待下去,这对系统资源是极大的浪费。因此,在需要处理大量连接的服务端,linger的值一定不可过大。

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