#include#include #define PORT 5150#define MSGSIZE 1024#pragma comment(lib, "ws2_32.lib")typedef struct{WSAOVERLAPPED overlap;WSABUF Buffer; char szMessage[MSGSIZE];DWORD NumberOfBytesRecvd;DWORD Flags;SOCKET sClient;}PER_IO_OPERATION_DATA, *LPPER_IO_OPERATION_DATA;DWORD WINAPI WorkerThread(LPVOID);void CALLBACK CompletionROUTINE(DWORD, DWORD, LPWSAOVERLAPPED, DWORD);SOCKET g_sNewClientConnection;BOOL g_bNewConnectionArrived = FALSE;int main(){ WSADATA wsaData; SOCKET sListen; SOCKADDR_IN local, client; DWORD dwThreadId; int iaddrSize = sizeof(SOCKADDR_IN); // Initialize Windows Socket library WSAStartup(0x0202, &wsaData); // Create listening socket sListen = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP); // Bind local.sin_addr.S_un.S_addr = htonl(INADDR_ANY);local.sin_family = AF_INET;local.sin_port = htons(PORT); bind(sListen, (struct sockaddr *)&local, sizeof(SOCKADDR_IN)); // Listen listen(sListen, 3); // Create worker thread CreateThread(NULL, 0, WorkerThread, NULL, 0, &dwThreadId); while (TRUE) { // Accept a connection g_sNewClientConnection = accept(sListen, (struct sockaddr *)&client, &iaddrSize); g_bNewConnectionArrived = TRUE; printf("Accepted client:%s:%d\n", inet_ntoa(client.sin_addr), ntohs(client.sin_port)); }}DWORD WINAPI WorkerThread(LPVOID lpParam){LPPER_IO_OPERATION_DATA lpPerIOData = NULL; while (TRUE) { if (g_bNewConnectionArrived) { // Launch an asynchronous operation for new arrived connection lpPerIOData = (LPPER_IO_OPERATION_DATA)HeapAlloc( GetProcessHeap(), HEAP_ZERO_MEMORY, sizeof(PER_IO_OPERATION_DATA)); lpPerIOData->Buffer.len = MSGSIZE; lpPerIOData->Buffer.buf = lpPerIOData->szMessage; lpPerIOData->sClient = g_sNewClientConnection; WSARecv(lpPerIOData->sClient, &lpPerIOData->Buffer, 1, &lpPerIOData->NumberOfBytesRecvd, &lpPerIOData->Flags, &lpPerIOData->overlap, CompletionROUTINE); g_bNewConnectionArrived = FALSE; } SleepEx(1000, TRUE); //这里如果不sleep,根本不会进入完成例程的回调,第一个参数时间可以适当缩小 } return 0;}void CALLBACK CompletionROUTINE(DWORD dwError, DWORD cbTransferred, LPWSAOVERLAPPED lpOverlapped, DWORD dwFlags){ LPPER_IO_OPERATION_DATA lpPerIOData = (LPPER_IO_OPERATION_DATA)lpOverlapped; if (dwError != 0 || cbTransferred == 0) { // Connection was closed by client closesocket(lpPerIOData->sClient); HeapFree(GetProcessHeap(), 0, lpPerIOData); } else { lpPerIOData->szMessage[cbTransferred] = '\0'; send(lpPerIOData->sClient, lpPerIOData->szMessage, cbTransferred, 0); // Launch another asynchronous operation memset(&lpPerIOData->overlap, 0, sizeof(WSAOVERLAPPED)); lpPerIOData->Buffer.len = MSGSIZE; lpPerIOData->Buffer.buf = lpPerIOData->szMessage; WSARecv(lpPerIOData->sClient, &lpPerIOData->Buffer, 1, &lpPerIOData->NumberOfBytesRecvd, &lpPerIOData->Flags, &lpPerIOData->overlap, CompletionROUTINE); }}
这个模型中有两个函数可以交换着用，那就是WSAWaitForMultipleEvents()和SleepEx()函数，前者需要一个事件驱动，后者则不需要。是不是听起来后者比较厉害，当然不是，简单肯定是拿某种性能换来的，那就是当多client同时发出请求的时候，SleepEx如果等候时间设置成比较大的话，会造成client连接不上的现象。具体可以运行一下示例代码体会一下。
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，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）。
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。