Overlapped I/O模型--完成例程

Overlapped I/O 完成例程要求用户提供一个回调函数，发生新的网络事件的时候系统将执行这个函数。系统用WorkerRoutine函数处理接收到的数据。

  1 #include <WINSOCK2.H>
  2 #include <stdio.h>
  3
  4 #define PORT    5150
  5 #define MSGSIZE 1024
  6
  7 #pragma comment(lib, "ws2_32.lib")
  8
  9 typedef struct
10 {
11     WSAOVERLAPPED overlap;
12     WSABUF        Buffer;
13     char          szMessage[MSGSIZE];
14     DWORD         NumberOfBytesRecvd;
15     DWORD         Flags;
16     SOCKET        sClient;
17 }PER_IO_OPERATION_DATA, *LPPER_IO_OPERATION_DATA;
18
19 DWORD WINAPI WorkerThread(LPVOID);
20
21 void CALLBACK CompletionROUTINE(DWORD, DWORD, LPWSAOVERLAPPED, DWORD);
22
23 SOCKET g_sNewClientConnection;
24
25 BOOL   g_bNewConnectionArrived = FALSE;
26
27 int main()
28 {
29     WSADATA     wsaData;
30     SOCKET      sListen;
31     SOCKADDR_IN local, client;
32     DWORD       dwThreadId;
33     int         iaddrSize = sizeof(SOCKADDR_IN);
34     // Initialize Windows Socket library
35     WSAStartup(0x0202, &wsaData);
36     // Create listening socket
37     sListen = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);
38     // Bind
39     local.sin_addr.S_un.S_addr = htonl(INADDR_ANY);
40     local.sin_family = AF_INET;
41     local.sin_port = htons(PORT);
42     bind(sListen, (struct sockaddr *)&local, sizeof(SOCKADDR_IN));
43     // Listen
44     listen(sListen, 3);
45     // Create worker thread
46     CreateThread(NULL, 0, WorkerThread, NULL, 0, &dwThreadId);
47     while (TRUE)
48     {
49         // Accept a connection
50         g_sNewClientConnection = accept(sListen, (struct sockaddr *)&client, &iaddrSize);
51         g_bNewConnectionArrived = TRUE;
52         printf("Accepted client:%s:%d\n", inet_ntoa(client.sin_addr), ntohs(client.sin_port));
53     }
54 }
55 DWORD WINAPI WorkerThread(LPVOID lpParam)
56 {
57     LPPER_IO_OPERATION_DATA lpPerIOData = NULL;
58     while (TRUE)
59     {
60         if (g_bNewConnectionArrived)
61         {
62             // Launch an asynchronous operation for new arrived connection
63             lpPerIOData = (LPPER_IO_OPERATION_DATA)HeapAlloc(
64                 GetProcessHeap(),HEAP_ZERO_MEMORY,sizeof(PER_IO_OPERATION_DATA));
65
66             lpPerIOData->Buffer.len = MSGSIZE;
67             lpPerIOData->Buffer.buf = lpPerIOData->szMessage;
68             lpPerIOData->sClient = g_sNewClientConnection;
69
70             WSARecv(lpPerIOData->sClient,
71                 &lpPerIOData->Buffer,
72                 1,
73                 &lpPerIOData->NumberOfBytesRecvd,
74                 &lpPerIOData->Flags,
75                 &lpPerIOData->overlap,
76                 CompletionROUTINE);
77
78             g_bNewConnectionArrived = FALSE;//这很重要

79 }

Sleep()是不可唤醒的，也就是说一直睡到时间结束。
SleepEx()是可以唤醒的，可以被消息唤醒

The SleepEx function causes the current thread to enter a wait state until one of the following occurs: 

1）An I/O completion callback function is called 
2）An asynchronous procedure call (APC) is queued to the thread. 
3）The time-out interval elapses

80         SleepEx(1000, TRUE);
81     }
82     return 0;
83 }
84 void CALLBACK CompletionROUTINE(DWORD dwError,
85                                 DWORD cbTransferred,
86                                 LPWSAOVERLAPPED lpOverlapped,
87                                 DWORD dwFlags)
88 {
89     LPPER_IO_OPERATION_DATA lpPerIOData = (LPPER_IO_OPERATION_DATA)lpOverlapped;
90
91     if (dwError != 0 || cbTransferred == 0)
92     {
93         // Connection was closed by client
94         closesocket(lpPerIOData->sClient);
95         HeapFree(GetProcessHeap(), 0, lpPerIOData);
96     }
97     else
98     {
99         lpPerIOData->szMessage[cbTransferred] = '\0';
100         send(lpPerIOData->sClient, lpPerIOData->szMessage, cbTransferred, 0);
101
102         // Launch another asynchronous operation
103         memset(&lpPerIOData->overlap, 0, sizeof(WSAOVERLAPPED));
104         lpPerIOData->Buffer.len = MSGSIZE;
105         lpPerIOData->Buffer.buf = lpPerIOData->szMessage;
106         WSARecv(lpPerIOData->sClient,
107             &lpPerIOData->Buffer,
108             1,
109             &lpPerIOData->NumberOfBytesRecvd,
110             &lpPerIOData->Flags,
111             &lpPerIOData->overlap,
112             CompletionROUTINE);
113     }
114 }

用完成例程来实现重叠I/O比用事件通知简单得多。在这个模型中，主线程只用不停的接受连接即可；辅助线程判断有没有新的客户端连接被建立，如果有，就为那个客户端套接字激活一个异步的WSARecv操作，然后调用SleepEx使线程处于一种可警告的等待状态，（按我的理解就是辅助线程主动的放弃一段时间的CPU使用权，以防止一直处于阻塞状态）以使得I/O完成后CompletionROUTINE可以被内核调用。如果辅助线程不调用SleepEx，则内核在完成一次I/O操作后，无法调用完成例程（因为完成例程的运行应该和当初激活WSARecv异步操作的代码在同一个线程之内）。当重叠IO操作完成，SleepEx会被完成的消息唤醒，从而使得辅助线程中的完成例程得到执行。

完成例程内的实现代码比较简单，它取出接收到的数据，然后将数据原封不动的发送给客户端，最后重新激活另一个WSARecv异步操作。注
意，在这里用到了“尾随数据”。我们在调用WSARecv的时候，参数lpOverlapped实际上指向一个比它大得多的结构PER_IO_OPERATION_DATA，这个结构除了WSAOVERLAPPED以外，还被我们附加了缓冲区的结构信息，另外还包括客户端套接字等重要的信息。这样，在完成例程中通过参数lpOverlapped拿到的不仅仅是WSAOVERLAPPED结构，还有后边尾随的包含客户端套接字和接收数据缓冲区等重要信息。这样的C语言技巧在我后面介绍完成端口的时候还会使用到。

的

来源：https://www.cnblogs.com/NeuqUstcIim/archive/2008/08/17/1269678.html

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