凡科建站代理入口,家装网站模板下载,网站建设程序开发过程,网站建设咋做引言之前的一篇介绍IO 模型的文章IO 模型知多少 -- 理论篇比较偏理论#xff0c;很多同学反应不是很好理解。这一篇咱们换一个角度#xff0c;从代码角度来分析一下。socket 编程基础开始之前#xff0c;我们先来梳理一下#xff0c;需要提前了解的几个概念#xff1a;soc… 引言之前的一篇介绍IO 模型的文章IO 模型知多少 -- 理论篇比较偏理论很多同学反应不是很好理解。这一篇咱们换一个角度从代码角度来分析一下。socket 编程基础开始之前我们先来梳理一下需要提前了解的几个概念socket: 直译为“插座”在计算机通信领域socket 被翻译为“套接字”它是计算机之间进行通信的一种约定或一种方式。通过 socket 这种约定一台计算机可以接收其他计算机的数据也可以向其他计算机发送数据。我们把插头插到插座上就能从电网获得电力供应同样应用程序为了与远程计算机进行数据传输需要连接到因特网而 socket 就是用来连接到因特网的工具。另外还需要知道的是socket 编程的基本流程。2. 同步阻塞IO先回顾下概念阻塞IO是指应用进程中线程在发起IO调用后至内核执行IO操作返回结果之前若发起系统调用的线程一直处于等待状态则此次IO操作为阻塞IO。public static void Start()
{//1. 创建Tcp Socket对象var serverSocket new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp);var ipEndpoint new IPEndPoint(IPAddress.Loopback, 5001);//2. 绑定Ip端口serverSocket.Bind(ipEndpoint);//3. 开启监听指定最大连接数serverSocket.Listen(10);Console.WriteLine($服务端已启动({ipEndpoint})-等待连接...);while (true){//4. 等待客户端连接var clientSocket serverSocket.Accept();//阻塞Console.WriteLine(${clientSocket.RemoteEndPoint}-已连接);Spanbyte buffer new Spanbyte(new byte[512]);Console.WriteLine(${clientSocket.RemoteEndPoint}-开始接收数据...);int readLength clientSocket.Receive(buffer);//阻塞var msg Encoding.UTF8.GetString(buffer.ToArray(), 0, readLength);Console.WriteLine(${clientSocket.RemoteEndPoint}-接收数据{msg});var sendBuffer Encoding.UTF8.GetBytes($received:{msg});clientSocket.Send(sendBuffer);}
}
代码很简单直接看注释就OK了运行结果如上图所示但有几个问题点需要着重说明下等待连接处 serverSocket.Accept()线程阻塞接收数据处 clientSocket.Receive(buffer)线程阻塞会导致什么问题呢只有一次数据读取完成后才可以接受下一个连接请求一个连接只能接收一次数据同步非阻塞IO看完你可能会说这两个问题很好解决啊创建一个新线程去接收数据就是了。于是就有了下面的代码改进。public static void Start2()
{//1. 创建Tcp Socket对象var serverSocket new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp);var ipEndpoint new IPEndPoint(IPAddress.Loopback, 5001);//2. 绑定Ip端口serverSocket.Bind(ipEndpoint);//3. 开启监听指定最大连接数serverSocket.Listen(10);Console.WriteLine($服务端已启动({ipEndpoint})-等待连接...);while (true){//4. 等待客户端连接var clientSocket serverSocket.Accept();//阻塞Task.Run(() ReceiveData(clientSocket));}
}
private static void ReceiveData(Socket clientSocket)
{Console.WriteLine(${clientSocket.RemoteEndPoint}-已连接);Spanbyte buffer new Spanbyte(new byte[512]);while (true){if (clientSocket.Available 0) continue;Console.WriteLine(${clientSocket.RemoteEndPoint}-开始接收数据...);int readLength clientSocket.Receive(buffer);//阻塞var msg Encoding.UTF8.GetString(buffer.ToArray(), 0, readLength);Console.WriteLine(${clientSocket.RemoteEndPoint}-接收数据{msg});var sendBuffer Encoding.UTF8.GetBytes($received:{msg});clientSocket.Send(sendBuffer);}
}
是的多线程解决了上述的问题但如果你观察以上动图后你应该能发现个问题才建立4个客户端连接CPU的占用率就开始直线上升了。而这个问题的本质就是服务端的IO模型为阻塞IO模型为了解决阻塞导致的问题采用重复轮询导致无效的系统调用从而导致CPU持续走高。IO多路复用既然知道原因所在咱们就来予以改造。适用异步方式来处理连接、接收和发送数据。public static class NioServer
{private static ManualResetEvent _acceptEvent new ManualResetEvent(true);private static ManualResetEvent _readEvent new ManualResetEvent(true);public static void Start(){//1. 创建Tcp Socket对象var serverSocket new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp);// serverSocket.Blocking false;//设置为非阻塞var ipEndpoint new IPEndPoint(IPAddress.Loopback, 5001);//2. 绑定Ip端口serverSocket.Bind(ipEndpoint);//3. 开启监听指定最大连接数serverSocket.Listen(10);Console.WriteLine($服务端已启动({ipEndpoint})-等待连接...);while (true){_acceptEvent.Reset();//重置信号量serverSocket.BeginAccept(OnClientConnected, serverSocket);_acceptEvent.WaitOne();//阻塞}}private static void OnClientConnected(IAsyncResult ar){_acceptEvent.Set();//当有客户端连接进来后则释放信号量var serverSocket ar.AsyncState as Socket;Debug.Assert(serverSocket ! null, nameof(serverSocket) ! null);var clientSocket serverSocket.EndAccept(ar);Console.WriteLine(${clientSocket.RemoteEndPoint}-已连接);while (true){_readEvent.Reset();//重置信号量var stateObj new StateObject { ClientSocket clientSocket };clientSocket.BeginReceive(stateObj.Buffer, 0, stateObj.Buffer.Length, SocketFlags.None, OnMessageReceived, stateObj);_readEvent.WaitOne();//阻塞等待}}private static void OnMessageReceived(IAsyncResult ar){var state ar.AsyncState as StateObject;Debug.Assert(state ! null, nameof(state) ! null);var receiveLength state.ClientSocket.EndReceive(ar);if (receiveLength 0){var msg Encoding.UTF8.GetString(state.Buffer, 0, receiveLength);Console.WriteLine(${state.ClientSocket.RemoteEndPoint}-接收数据{msg});var sendBuffer Encoding.UTF8.GetBytes($received:{msg});state.ClientSocket.BeginSend(sendBuffer, 0, sendBuffer.Length, SocketFlags.None,SendMessage, state.ClientSocket);}}private static void SendMessage(IAsyncResult ar){var clientSocket ar.AsyncState as Socket;Debug.Assert(clientSocket ! null, nameof(clientSocket) ! null);clientSocket.EndSend(ar);_readEvent.Set(); //发送完毕后释放信号量}
}
public class StateObject
{// Client socket. public Socket ClientSocket null;// Size of receive buffer. public const int BufferSize 1024;// Receive buffer. public byte[] Buffer new byte[BufferSize];
}
首先来看运行结果从下图可以看到除了建立连接时CPU出现抖动外在消息接收和发送阶段CPU占有率趋于平缓且占用率低。分析代码后我们发现CPU使用率是下来了但代码复杂度上升了。使用异步接口处理客户端连接 BeginAccept和 EndAccept使用异步接口接收数据 BeginReceive和 EndReceive使用异步接口发送数据 BeginSend和 EndSend使用 ManualResetEvent进行线程同步避免线程空转那你可能好奇以上模型是何种IO多路复用模型呢 好问题我们来一探究竟。验证I/O模型要想验证应用使用的何种IO模型只需要确定应用运行时发起了哪些系统调用即可。对于Linux系统来说我们可以借助 strace命令来跟踪指定应用发起的系统调用和信号。验证同步阻塞I/O发起的系统调用可以使用VSCode Remote 连接到自己的Linux系统上然后新建项目 Io.Demo以上面非阻塞IO的代码进行测试执行以下启动跟踪命令shengjieubuntu:~/coding/dotnet$ ls
Io.Demo
shengjieubuntu:~/coding/dotnet$ strace -ff -o Io.Demo/strace/io dotnet run --project Io.Demo/
Press any key to start!
服务端已启动(127.0.0.1:5001)-等待连接...
127.0.0.1:36876-已连接
127.0.0.1:36876-开始接收数据...
127.0.0.1:36876-接收数据1
另起命令行执行 nc localhost5001模拟客户端连接。shengjieubuntu:~/coding/dotnet/Io.Demo$ nc localhost 5001
1
received:1
使用 netstat命令查看建立的连接。shengjieubuntu:/proc/3763$ netstat -natp | grep 5001
(Not all processes could be identified, non-owned process infowill not be shown, you would have to be root to see it all.)
tcp 0 0 127.0.0.1:5001 0.0.0.0:* LISTEN 3763/Io.Demo
tcp 0 0 127.0.0.1:36920 127.0.0.1:5001 ESTABLISHED 3798/nc
tcp 0 0 127.0.0.1:5001 127.0.0.1:36920 ESTABLISHED 3763/Io.Demo
另起命令行执行 ps-h|grep dotnet 抓取进程Id。shengjieubuntu:~/coding/dotnet/Io.Demo$ ps -h | grep dotnet3694 pts/1 S 0:11 strace -ff -o Io.Demo/strace/io dotnet run --project Io.Demo/3696 pts/1 Sl 0:01 dotnet run --project Io.Demo/3763 pts/1 Sl 0:00 /home/shengjie/coding/dotnet/Io.Demo/bin/Debug/netcoreapp3.0/Io.Demo3779 pts/2 S 0:00 grep --colorauto dotnet
shengjieubuntu:~/coding/dotnet$ ls Io.Demo/strace/ # 查看生成的系统调用文件
io.3696 io.3702 io.3708 io.3714 io.3720 io.3726 io.3732 io.3738 io.3744 io.3750 io.3766 io.3772 io.3782 io.3827
io.3697 io.3703 io.3709 io.3715 io.3721 io.3727 io.3733 io.3739 io.3745 io.3751 io.3767 io.3773 io.3786 io.3828
io.3698 io.3704 io.3710 io.3716 io.3722 io.3728 io.3734 io.3740 io.3746 io.3752 io.3768 io.3774 io.3787
io.3699 io.3705 io.3711 io.3717 io.3723 io.3729 io.3735 io.3741 io.3747 io.3763 io.3769 io.3777 io.3797
io.3700 io.3706 io.3712 io.3718 io.3724 io.3730 io.3736 io.3742 io.3748 io.3764 io.3770 io.3780 io.3799
io.3701 io.3707 io.3713 io.3719 io.3725 io.3731 io.3737 io.3743 io.3749 io.3765 io.3771 io.3781 io.3800
有上可知进程Id为3763依次执行以下命令可以查看该进程的线程和产生的文件描述符shengjieubuntu:~/coding/dotnet/Io.Demo$ cd /proc/3763 # 进入进程目录
shengjieubuntu:/proc/3763$ ls
attr cmdline environ io mem ns pagemap sched smaps_rollup syscall wchan
autogroup comm exe limits mountinfo numa_maps patch_state schedstat stack task
auxv coredump_filter fd loginuid mounts oom_adj personality sessionid stat timers
cgroup cpuset fdinfo map_files mountstats oom_score projid_map setgroups statm timerslack_ns
clear_refs cwd gid_map maps net oom_score_adj root smaps status uid_map
shengjieubuntu:/proc/3763$ ll task # 查看当前进程启动的线程
total 0
dr-xr-xr-x 9 shengjie shengjie 0 5月 10 16:36 ./
dr-xr-xr-x 9 shengjie shengjie 0 5月 10 16:34 ../
dr-xr-xr-x 7 shengjie shengjie 0 5月 10 16:36 3763/
dr-xr-xr-x 7 shengjie shengjie 0 5月 10 16:36 3765/
dr-xr-xr-x 7 shengjie shengjie 0 5月 10 16:36 3766/
dr-xr-xr-x 7 shengjie shengjie 0 5月 10 16:36 3767/
dr-xr-xr-x 7 shengjie shengjie 0 5月 10 16:36 3768/
dr-xr-xr-x 7 shengjie shengjie 0 5月 10 16:36 3769/
dr-xr-xr-x 7 shengjie shengjie 0 5月 10 16:36 3770/
shengjieubuntu:/proc/3763$ ll fd 查看当前进程系统调用产生的文件描述符
total 0
dr-x------ 2 shengjie shengjie 0 5月 10 16:36 ./
dr-xr-xr-x 9 shengjie shengjie 0 5月 10 16:34 ../
lrwx------ 1 shengjie shengjie 64 5月 10 16:37 0 - /dev/pts/1
lrwx------ 1 shengjie shengjie 64 5月 10 16:37 1 - /dev/pts/1
lrwx------ 1 shengjie shengjie 64 5月 10 16:37 10 - socket:[44292]
lr-x------ 1 shengjie shengjie 64 5月 10 16:37 100 - /dev/random
lrwx------ 1 shengjie shengjie 64 5月 10 16:37 11 - socket:[41675]
lr-x------ 1 shengjie shengjie 64 5月 10 16:37 13 - pipe:[45206]
l-wx------ 1 shengjie shengjie 64 5月 10 16:37 14 - pipe:[45206]
lr-x------ 1 shengjie shengjie 64 5月 10 16:37 15 - /home/shengjie/coding/dotnet/Io.Demo/bin/Debug/netcoreapp3.0/Io.Demo.dll
lr-x------ 1 shengjie shengjie 64 5月 10 16:37 16 - /home/shengjie/coding/dotnet/Io.Demo/bin/Debug/netcoreapp3.0/Io.Demo.dll
lr-x------ 1 shengjie shengjie 64 5月 10 16:37 17 - /usr/share/dotnet/shared/Microsoft.NETCore.App/3.0.0/System.Runtime.dll
lr-x------ 1 shengjie shengjie 64 5月 10 16:37 18 - /usr/share/dotnet/shared/Microsoft.NETCore.App/3.0.0/System.Console.dll
lr-x------ 1 shengjie shengjie 64 5月 10 16:37 19 - /usr/share/dotnet/shared/Microsoft.NETCore.App/3.0.0/System.Threading.dll
lrwx------ 1 shengjie shengjie 64 5月 10 16:37 2 - /dev/pts/1
lr-x------ 1 shengjie shengjie 64 5月 10 16:37 20 - /usr/share/dotnet/shared/Microsoft.NETCore.App/3.0.0/System.Runtime.Extensions.dll
lrwx------ 1 shengjie shengjie 64 5月 10 16:37 21 - /dev/pts/1
lr-x------ 1 shengjie shengjie 64 5月 10 16:37 22 - /usr/share/dotnet/shared/Microsoft.NETCore.App/3.0.0/System.Text.Encoding.Extensions.dll
lr-x------ 1 shengjie shengjie 64 5月 10 16:37 23 - /dev/urandom
lr-x------ 1 shengjie shengjie 64 5月 10 16:37 24 - /usr/share/dotnet/shared/Microsoft.NETCore.App/3.0.0/System.Net.Sockets.dll
lr-x------ 1 shengjie shengjie 64 5月 10 16:37 25 - /usr/share/dotnet/shared/Microsoft.NETCore.App/3.0.0/System.Net.Primitives.dll
lr-x------ 1 shengjie shengjie 64 5月 10 16:37 26 - /usr/share/dotnet/shared/Microsoft.NETCore.App/3.0.0/Microsoft.Win32.Primitives.dll
lr-x------ 1 shengjie shengjie 64 5月 10 16:37 27 - /usr/share/dotnet/shared/Microsoft.NETCore.App/3.0.0/System.Diagnostics.Tracing.dll
lr-x------ 1 shengjie shengjie 64 5月 10 16:37 28 - /usr/share/dotnet/shared/Microsoft.NETCore.App/3.0.0/System.Threading.Tasks.dll
lrwx------ 1 shengjie shengjie 64 5月 10 16:37 29 - socket:[43429]
lr-x------ 1 shengjie shengjie 64 5月 10 16:37 3 - pipe:[42148]
lr-x------ 1 shengjie shengjie 64 5月 10 16:37 30 - /usr/share/dotnet/shared/Microsoft.NETCore.App/3.0.0/System.Threading.ThreadPool.dll
lrwx------ 1 shengjie shengjie 64 5月 10 16:37 31 - socket:[42149]
lr-x------ 1 shengjie shengjie 64 5月 10 16:37 32 - /usr/share/dotnet/shared/Microsoft.NETCore.App/3.0.0/System.Memory.dll
l-wx------ 1 shengjie shengjie 64 5月 10 16:37 4 - pipe:[42148]
lr-x------ 1 shengjie shengjie 64 5月 10 16:37 42 - /dev/urandom
lrwx------ 1 shengjie shengjie 64 5月 10 16:37 5 - /dev/pts/1
lrwx------ 1 shengjie shengjie 64 5月 10 16:37 6 - /dev/pts/1
lrwx------ 1 shengjie shengjie 64 5月 10 16:37 7 - /dev/pts/1
lr-x------ 1 shengjie shengjie 64 5月 10 16:37 9 - /usr/share/dotnet/shared/Microsoft.NETCore.App/3.0.0/System.Private.CoreLib.dll
lr-x------ 1 shengjie shengjie 64 5月 10 16:37 99 - /dev/urandom
从上面的输出来看.NET Core控制台应用启动时启动了多个线程并在10、11、29、31号文件描述符启动了socket监听。那哪一个文件描述符监听的是5001端口呢。shengjieubuntu:~/coding/dotnet/Io.Demo$ cat /proc/net/tcp | grep 1389 # 查看5001端口号相关的tcp链接0x1389 为5001十六进制)4: 0100007F:1389 00000000:0000 0A 00000000:00000000 00:00000000 00000000 1000 0 43429 1 0000000000000000 100 0 0 10 0 12: 0100007F:9038 0100007F:1389 01 00000000:00000000 00:00000000 00000000 1000 0 44343 1 0000000000000000 20 4 30 10 -1 13: 0100007F:1389 0100007F:9038 01 00000000:00000000 00:00000000 00000000 1000 0 42149 1 0000000000000000 20 4 29 10 -1
从中可以看到inode为[43429]的socket监听在5001端口号所以可以找到上面的输出行 lrwx------1shengjie shengjie645月1016:3729-socket:[43429]进而判断监听5001端口号socket对应的文件描述符为29。当然也可以从记录到 strace目录的日志文件找到线索。在文中我们已经提及socket服务端编程的一般流程都要经过socket-bind-accept-read-write流程。所以可以通过抓取关键字查看相关系统调用。shengjieubuntu:~/coding/dotnet/Io.Demo$ grep bind strace/ -rn
strace/io.3696:4570:bind(10, {sa_familyAF_UNIX, sun_path/tmp/dotnet-diagnostic-3696-327175-socket}, 110) 0
strace/io.3763:2241:bind(11, {sa_familyAF_UNIX, sun_path/tmp/dotnet-diagnostic-3763-328365-socket}, 110) 0
strace/io.3763:2949:bind(29, {sa_familyAF_INET, sin_porthtons(5001), sin_addrinet_addr(127.0.0.1)}, 16) 0
strace/io.3713:4634:bind(11, {sa_familyAF_UNIX, sun_path/tmp/dotnet-diagnostic-3713-327405-socket}, 110) 0
从上可知在主线程也就是 io.3763线程的系统调用文件中将29号文件描述符与监听在 127.0.0.1:5001的socket进行了绑定。同时也明白了.NET Core自动建立的另外2个socket是与diagnostic相关。 接下来咱们重点看下3763号线程产生的系统调用。shengjieubuntu:~/coding/dotnet/Io.Demo$ cd strace/
shengjieubuntu:~/coding/dotnet/Io.Demo/strace$ cat io.3763 # 仅截取相关片段
socket(AF_INET, SOCK_STREAM|SOCK_CLOEXEC, IPPROTO_TCP) 29
setsockopt(29, SOL_SOCKET, SO_REUSEADDR, [1], 4) 0
bind(29, {sa_familyAF_INET, sin_porthtons(5001), sin_addrinet_addr(127.0.0.1)}, 16) 0
listen(29, 10)
write(21, \346\234\215\345\212\241\347\253\257\345\267\262\345\220\257\345\212\250(127.0.0.1:500..., 51) 51
accept4(29, {sa_familyAF_INET, sin_porthtons(36920), sin_addrinet_addr(127.0.0.1)}, [16], SOCK_CLOEXEC) 31
write(21, 127.0.0.1:36920-\345\267\262\350\277\236\346\216\245\n, 26) 26
write(21, 127.0.0.1:36920-\345\274\200\345\247\213\346\216\245\346\224\266\346\225\260\346..., 38) 38
recvmsg(31, {msg_nameNULL, msg_namelen0, msg_iov[{iov_base1\n, iov_len512}], msg_iovlen1, msg_controllen0, msg_flags0}, 0) 2
write(21, 127.0.0.1:36920-\346\216\245\346\224\266\346\225\260\346\215\256\357\274\2321..., 34) 34
sendmsg(31, {msg_nameNULL, msg_namelen0, msg_iov[{iov_basereceived:1\n, iov_len11}], msg_iovlen1, msg_controllen0, msg_flags0}, 0) 11
accept4(29, 0x7fecf001c978, [16], SOCK_CLOEXEC) ? ERESTARTSYS (To be restarted if SA_RESTART is set)
--- SIGWINCH {si_signoSIGWINCH, si_codeSI_KERNEL} ---
从中我们可以发现几个关键的系统调用socket、bind、listen、accept4、recvmsg、sendmsg 通过命令 man命令可以查看下 accept4和 recvmsg系统调用的相关说明shengjieubuntu:~/coding/dotnet/Io.Demo/strace$ man accept4
If no pending connections are present on the queue, and the socket is not marked as nonblocking, accept() blocks the caller until aconnection is present.
shengjieubuntu:~/coding/dotnet/Io.Demo/strace$ man recvmsg
If no messages are available at the socket, the receive calls wait for a message to arrive, unless the socket is nonblocking (see fcntl(2))
也就是说 accept4和 recvmsg是阻塞式系统调用。验证I/O多路复用发起的系统调用同样以上面I/O多路复用的代码进行验证验证步骤类似shengjieubuntu:~/coding/dotnet$ strace -ff -o Io.Demo/strace2/io dotnet run --project Io.Demo/
Press any key to start!
服务端已启动(127.0.0.1:5001)-等待连接...
127.0.0.1:37098-已连接
127.0.0.1:37098-接收数据1
127.0.0.1:37098-接收数据2
shengjieubuntu:~/coding/dotnet/Io.Demo$ nc localhost 5001
1
received:1
2
received:2
shengjieubuntu:/proc/2449$ netstat -natp | grep 5001
(Not all processes could be identified, non-owned process infowill not be shown, you would have to be root to see it all.)
tcp 0 0 127.0.0.1:5001 0.0.0.0:* LISTEN 2449/Io.Demo
tcp 0 0 127.0.0.1:5001 127.0.0.1:56296 ESTABLISHED 2449/Io.Demo
tcp 0 0 127.0.0.1:56296 127.0.0.1:5001 ESTABLISHED 2499/nc
shengjieubuntu:~/coding/dotnet/Io.Demo$ ps -h | grep dotnet2400 pts/3 S 0:10 strace -ff -o ./Io.Demo/strace2/io dotnet run --project Io.Demo/2402 pts/3 Sl 0:01 dotnet run --project Io.Demo/2449 pts/3 Sl 0:00 /home/shengjie/coding/dotnet/Io.Demo/bin/Debug/netcoreapp3.0/Io.Demo2516 pts/5 S 0:00 grep --colorauto dotnet
shengjieubuntu:~/coding/dotnet/Io.Demo$ cd /proc/2449/
shengjieubuntu:/proc/2449$ ll task
total 0
dr-xr-xr-x 11 shengjie shengjie 0 5月 10 22:15 ./
dr-xr-xr-x 9 shengjie shengjie 0 5月 10 22:15 ../
dr-xr-xr-x 7 shengjie shengjie 0 5月 10 22:15 2449/
dr-xr-xr-x 7 shengjie shengjie 0 5月 10 22:15 2451/
dr-xr-xr-x 7 shengjie shengjie 0 5月 10 22:15 2452/
dr-xr-xr-x 7 shengjie shengjie 0 5月 10 22:15 2453/
dr-xr-xr-x 7 shengjie shengjie 0 5月 10 22:15 2454/
dr-xr-xr-x 7 shengjie shengjie 0 5月 10 22:15 2455/
dr-xr-xr-x 7 shengjie shengjie 0 5月 10 22:15 2456/
dr-xr-xr-x 7 shengjie shengjie 0 5月 10 22:15 2459/
dr-xr-xr-x 7 shengjie shengjie 0 5月 10 22:15 2462/
shengjieubuntu:/proc/2449$ ll fd
total 0
dr-x------ 2 shengjie shengjie 0 5月 10 22:15 ./
dr-xr-xr-x 9 shengjie shengjie 0 5月 10 22:15 ../
lrwx------ 1 shengjie shengjie 64 5月 10 22:16 0 - /dev/pts/3
lrwx------ 1 shengjie shengjie 64 5月 10 22:16 1 - /dev/pts/3
lrwx------ 1 shengjie shengjie 64 5月 10 22:16 10 - socket:[35001]
lr-x------ 1 shengjie shengjie 64 5月 10 22:16 100 - /dev/random
lrwx------ 1 shengjie shengjie 64 5月 10 22:16 11 - socket:[34304]
lr-x------ 1 shengjie shengjie 64 5月 10 22:16 13 - pipe:[31528]
l-wx------ 1 shengjie shengjie 64 5月 10 22:16 14 - pipe:[31528]
lr-x------ 1 shengjie shengjie 64 5月 10 22:16 15 - /home/shengjie/coding/dotnet/Io.Demo/bin/Debug/netcoreapp3.0/Io.Demo.dll
lr-x------ 1 shengjie shengjie 64 5月 10 22:16 16 - /home/shengjie/coding/dotnet/Io.Demo/bin/Debug/netcoreapp3.0/Io.Demo.dll
lr-x------ 1 shengjie shengjie 64 5月 10 22:16 17 - /usr/share/dotnet/shared/Microsoft.NETCore.App/3.0.0/System.Runtime.dll
lr-x------ 1 shengjie shengjie 64 5月 10 22:16 18 - /usr/share/dotnet/shared/Microsoft.NETCore.App/3.0.0/System.Console.dll
lr-x------ 1 shengjie shengjie 64 5月 10 22:16 19 - /usr/share/dotnet/shared/Microsoft.NETCore.App/3.0.0/System.Threading.dll
lrwx------ 1 shengjie shengjie 64 5月 10 22:16 2 - /dev/pts/3
lr-x------ 1 shengjie shengjie 64 5月 10 22:16 20 - /usr/share/dotnet/shared/Microsoft.NETCore.App/3.0.0/System.Runtime.Extensions.dll
lrwx------ 1 shengjie shengjie 64 5月 10 22:16 21 - /dev/pts/3
lr-x------ 1 shengjie shengjie 64 5月 10 22:16 22 - /usr/share/dotnet/shared/Microsoft.NETCore.App/3.0.0/System.Text.Encoding.Extensions.dll
lr-x------ 1 shengjie shengjie 64 5月 10 22:16 23 - /dev/urandom
lr-x------ 1 shengjie shengjie 64 5月 10 22:16 24 - /usr/share/dotnet/shared/Microsoft.NETCore.App/3.0.0/System.Net.Sockets.dll
lr-x------ 1 shengjie shengjie 64 5月 10 22:16 25 - /usr/share/dotnet/shared/Microsoft.NETCore.App/3.0.0/System.Net.Primitives.dll
lr-x------ 1 shengjie shengjie 64 5月 10 22:16 26 - /usr/share/dotnet/shared/Microsoft.NETCore.App/3.0.0/Microsoft.Win32.Primitives.dll
lr-x------ 1 shengjie shengjie 64 5月 10 22:16 27 - /usr/share/dotnet/shared/Microsoft.NETCore.App/3.0.0/System.Diagnostics.Tracing.dll
lr-x------ 1 shengjie shengjie 64 5月 10 22:16 28 - /usr/share/dotnet/shared/Microsoft.NETCore.App/3.0.0/System.Threading.Tasks.dll
lrwx------ 1 shengjie shengjie 64 5月 10 22:16 29 - socket:[31529]
lr-x------ 1 shengjie shengjie 64 5月 10 22:16 3 - pipe:[32055]
lr-x------ 1 shengjie shengjie 64 5月 10 22:16 30 - /usr/share/dotnet/shared/Microsoft.NETCore.App/3.0.0/System.Threading.ThreadPool.dll
lr-x------ 1 shengjie shengjie 64 5月 10 22:16 31 - /usr/share/dotnet/shared/Microsoft.NETCore.App/3.0.0/System.Collections.Concurrent.dll
lrwx------ 1 shengjie shengjie 64 5月 10 22:16 32 - anon_inode:[eventpoll]
lr-x------ 1 shengjie shengjie 64 5月 10 22:16 33 - pipe:[32059]
l-wx------ 1 shengjie shengjie 64 5月 10 22:16 34 - pipe:[32059]
lrwx------ 1 shengjie shengjie 64 5月 10 22:16 35 - socket:[35017]
lr-x------ 1 shengjie shengjie 64 5月 10 22:16 36 - /usr/share/dotnet/shared/Microsoft.NETCore.App/3.0.0/System.Memory.dll
lr-x------ 1 shengjie shengjie 64 5月 10 22:16 37 - /dev/urandom
lr-x------ 1 shengjie shengjie 64 5月 10 22:16 38 - /usr/share/dotnet/shared/Microsoft.NETCore.App/3.0.0/System.Diagnostics.Debug.dll
l-wx------ 1 shengjie shengjie 64 5月 10 22:16 4 - pipe:[32055]
lrwx------ 1 shengjie shengjie 64 5月 10 22:16 5 - /dev/pts/3
lrwx------ 1 shengjie shengjie 64 5月 10 22:16 6 - /dev/pts/3
lrwx------ 1 shengjie shengjie 64 5月 10 22:16 7 - /dev/pts/3
lr-x------ 1 shengjie shengjie 64 5月 10 22:16 9 - /usr/share/dotnet/shared/Microsoft.NETCore.App/3.0.0/System.Private.CoreLib.dll
lr-x------ 1 shengjie shengjie 64 5月 10 22:16 99 - /dev/urandom
shengjieubuntu:/proc/2449$ cat /proc/net/tcp | grep 13890: 0100007F:1389 00000000:0000 0A 00000000:00000000 00:00000000 00000000 1000 0 31529 1 0000000000000000 100 0 0 10 0 8: 0100007F:1389 0100007F:DBE8 01 00000000:00000000 00:00000000 00000000 1000 0 35017 1 0000000000000000 20 4 29 10 -1 12: 0100007F:DBE8 0100007F:1389 01 00000000:00000000 00:00000000 00000000 1000 0 28496 1 0000000000000000 20 4 30 10 -1
过滤 strace2 目录日志抓取监听在 localhost:5001socket对应的文件描述符。shengjieubuntu:~/coding/dotnet/Io.Demo$ grep bind strace2/ -rn
strace2/io.2449:2243:bind(11, {sa_familyAF_UNIX, sun_path/tmp/dotnet-diagnostic-2449-23147-socket}, 110) 0
strace2/io.2449:2950:bind(29, {sa_familyAF_INET, sin_porthtons(5001), sin_addrinet_addr(127.0.0.1)}, 16) 0
strace2/io.2365:4568:bind(10, {sa_familyAF_UNIX, sun_path/tmp/dotnet-diagnostic-2365-19043-socket}, 110) 0
strace2/io.2420:4634:bind(11, {sa_familyAF_UNIX, sun_path/tmp/dotnet-diagnostic-2420-22262-socket}, 110) 0
strace2/io.2402:4569:bind(10, {sa_familyAF_UNIX, sun_path/tmp/dotnet-diagnostic-2402-22042-socket}, 110) 0
从中可以看出同样是29号文件描述符相关系统调用记录中 io.2449文件中打开文件可以发现相关系统调用如下shengjieubuntu:~/coding/dotnet/Io.Demo$ cat strace2/io.2449 # 截取相关系统调用
socket(AF_INET, SOCK_STREAM|SOCK_CLOEXEC, IPPROTO_TCP) 29
setsockopt(29, SOL_SOCKET, SO_REUSEADDR, [1], 4) 0
bind(29, {sa_familyAF_INET, sin_porthtons(5001), sin_addrinet_addr(127.0.0.1)}, 16) 0
listen(29, 10)
accept4(29, 0x7fa16c01b9e8, [16], SOCK_CLOEXEC) -1 EAGAIN (Resource temporarily unavailable)
epoll_create1(EPOLL_CLOEXEC) 32
epoll_ctl(32, EPOLL_CTL_ADD, 29, {EPOLLIN|EPOLLOUT|EPOLLET, {u320, u640}}) 0
accept4(29, 0x7fa16c01cd60, [16], SOCK_CLOEXEC) -1 EAGAIN (Resource temporarily unavailable)
从中我们可以发现 accept4直接返回-1而不阻塞监听在 127.0.0.1:5001的socket对应的29号文件描述符最终作为 epoll_ctl的参数关联到 epoll_create1创建的32号文件描述符上。最终32号文件描述符会被 epoll_wait阻塞以等待连接请求。我们可以抓取 epoll相关的系统调用来验证shengjieubuntu:~/coding/dotnet/Io.Demo$ grep epoll strace2/ -rn
strace2/io.2459:364:epoll_ctl(32, EPOLL_CTL_ADD, 35, {EPOLLIN|EPOLLOUT|EPOLLET, {u321, u641}}) 0
strace2/io.2462:21:epoll_wait(32, [{EPOLLIN, {u320, u640}}], 1024, -1) 1
strace2/io.2462:42:epoll_wait(32, [{EPOLLOUT, {u321, u641}}], 1024, -1) 1
strace2/io.2462:43:epoll_wait(32, [{EPOLLIN|EPOLLOUT, {u321, u641}}], 1024, -1) 1
strace2/io.2462:53:epoll_wait(32,
strace2/io.2449:3033:epoll_create1(EPOLL_CLOEXEC) 32
strace2/io.2449:3035:epoll_ctl(32, EPOLL_CTL_ADD, 33, {EPOLLIN|EPOLLET, {u324294967295, u6418446744073709551615}}) 0
strace2/io.2449:3061:epoll_ctl(32, EPOLL_CTL_ADD, 29, {EPOLLIN|EPOLLOUT|EPOLLET, {u320, u640}}) 0
因此我们可以断定同步非阻塞I/O的示例使用的时IO多路复用的epoll模型。关于epoll相关命令man命令可以查看下 epoll_create1、 epoll_ctl和、 epoll_wait系统调用的相关说明shengjieubuntu:~/coding/dotnet/Io.Demo/strace$ man epoll_create
DESCRIPTIONepoll_create() creates a new epoll(7) instance. Since Linux 2.6.8, the size argument is ignored, but must begreater than zero; see NOTES below.epoll_create() returns a file descriptor referring to the new epoll instance. This file descriptor is usedfor all the subsequent calls to the epoll interface.
shengjieubuntu:~/coding/dotnet/Io.Demo/strace$ man epoll_ctl
DESCRIPTIONThis system call performs control operations on the epoll(7) instance referred to by the file descriptorepfd. It requests that the operation op be performed for the target file descriptor, fd.Valid values for the op argument are:EPOLL_CTL_ADDRegister the target file descriptor fd on the epoll instance referred to by the file descriptor epfdand associate the event event with the internal file linked to fd.EPOLL_CTL_MODChange the event event associated with the target file descriptor fd.EPOLL_CTL_DELRemove (deregister) the target file descriptor fd from the epoll instance referred to by epfd. Theevent is ignored and can be NULL (but see BUGS below).
shengjieubuntu:~/coding/dotnet/Io.Demo/strace$ man epoll_wait
DESCRIPTIONThe epoll_wait() system call waits for events on the epoll(7) instance referred to by the file descriptorepfd. The memory area pointed to by events will contain the events that will be available for the caller.Up to maxevents are returned by epoll_wait(). The maxevents argument must be greater than zero.The timeout argument specifies the number of milliseconds that epoll_wait() will block. Time is measuredagainst the CLOCK_MONOTONIC clock. The call will block until either:* a file descriptor delivers an event;* the call is interrupted by a signal handler; or* the timeout expires.
简而言之epoll通过创建一个新的文件描述符来替换旧的文件描述符来完成阻塞工作当有事件或超时时通知原有文件描述符进行处理以实现非阻塞的线程模型。总结写完这篇文章对I/O模型的理解有所加深但由于对Linux系统的了解不深所以难免有纰漏之处大家多多指教。 同时也不仅感叹Linux的强大之处一切皆文件的设计思想让一切都有迹可循。现在.NET 已经完全实现跨平台了那么Linux操作系统大家就有必要熟悉起来了。
