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。