(四)Socket I/O模型之重叠I/O(overlapped I/O)
2013-04-23 18:27
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Winsock2的发布使得Socket I/O有了和文件I/O统一的接口。我们可以通过使用Win32文件操纵函数ReadFile和WriteFile来进行Socket I/O。伴随而来的,用于普通文件I/O的重叠I/O模型和完成端口模型对Socket I/O也适用了。这些模型的优点是可以达到更佳的系统性能,但是实现较为复杂,里面涉及较多的C语言技巧。例如我们在完成端口模型中会经常用到所谓的“尾随数据”。
一、用事件通知方式实现的重叠I/O 模型
这个模型与上述其他模型不同的是它使用Winsock2提供的异步I/O函数WSARecv。在调用WSARecv时,指定一个 WSAOVERLAPPED 结构,这个调用不是阻塞的,也就是说,它会立刻返回。一旦有数据到达的时候,被指定的WSAOVERLAPPED结构中的hEvent被 Signaled。由于下面这个语句
g_CliEventArr[g_iTotalConn] = g_pPerIODataArr[g_iTotalConn]->overlap.hEvent;
使得与该套接字相关联的WSAEVENT对象也被Signaled,所以WSAWaitForMultipleEvents的调用操作成功返回。我们现在应该做的就是用与调用WSARecv相同的WSAOVERLAPPED结构为参数调用WSAGetOverlappedResult,从而得到本次I/O 传送的字节数等相关信息。在取得接收的数据后,把数据原封不动的发送到客户端,然后重新激活一个WSARecv异步操作。
二、 用完成例程方式实现的重叠I/O 模型
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。
Winsock2的发布使得Socket I/O有了和文件I/O统一的接口。我们可以通过使用Win32文件操纵函数ReadFile和WriteFile来进行Socket I/O。伴随而来的,用于普通文件I/O的重叠I/O模型和完成端口模型对Socket I/O也适用了。这些模型的优点是可以达到更佳的系统性能,但是实现较为复杂,里面涉及较多的C语言技巧。例如我们在完成端口模型中会经常用到所谓的“尾随数据”。
一、用事件通知方式实现的重叠I/O 模型
// write by larry // 2009-8-20 // This is a server using overlapped IO(event notify). #include "stdafx.h" #include <WINSOCK2.H> #include <stdio.h> #pragma comment(lib, "ws2_32.lib") #define PORT 5150 #define MSGSIZE 1024 typedef struct { WSAOVERLAPPED overlap; WSABUF Buffer; char szMessage[MSGSIZE]; DWORD NumberOfBytesRecvd; DWORD Flags; } PER_IO_OPERATION_DATA, *LPPER_IO_OPERATION_DATA; int g_iTotalConn = 0; SOCKET g_CliSocketArr[MAXIMUM_WAIT_OBJECTS]; WSAEVENT g_CliEventArr[MAXIMUM_WAIT_OBJECTS]; LPPER_IO_OPERATION_DATA g_pPerIoDataArr[MAXIMUM_WAIT_OBJECTS]; DWORD WINAPI WorkerThread(LPVOID lpParam); void Cleanup(int index); int main(int argc, char* argv[]) { WSADATA wsaData; SOCKET sListen, sClient; 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_family = AF_INET; local.sin_addr.S_un.S_addr = htonl(INADDR_ANY); local.sin_port = htons(PORT); bind(sListen, (sockaddr*)&local, sizeof(SOCKADDR_IN)); // Listen listen(sListen, 3); // Create worker thread CreateThread(NULL, 0, WorkerThread, NULL, 0, &dwThreadId); while (TRUE) { // Accept a connection sClient = accept(sListen, (sockaddr*)&client, &iAddrSize); printf("Accepted client:%s:%d\n", inet_ntoa(client.sin_addr), ntohs(client.sin_port)); g_CliSocketArr[g_iTotalConn] = sClient; // Associate a PER_IO_OPERATION_DATA structure g_pPerIoDataArr[g_iTotalConn] = (LPPER_IO_OPERATION_DATA)HeapAlloc( GetProcessHeap(), HEAP_ZERO_MEMORY, sizeof(PER_IO_OPERATION_DATA)); g_pPerIoDataArr[g_iTotalConn]->Buffer.len = MSGSIZE; g_pPerIoDataArr[g_iTotalConn]->Buffer.buf = g_pPerIoDataArr[g_iTotalConn]->szMessage; g_CliEventArr[g_iTotalConn] = g_pPerIoDataArr[g_iTotalConn]->overlap.hEvent = WSACreateEvent(); // Launch an asynchronous operation WSARecv(g_CliSocketArr[g_iTotalConn], &g_pPerIoDataArr[g_iTotalConn]->Buffer, 1, &g_pPerIoDataArr[g_iTotalConn]->NumberOfBytesRecvd, &g_pPerIoDataArr[g_iTotalConn]->Flags, &g_pPerIoDataArr[g_iTotalConn]->overlap, NULL); g_iTotalConn++; } closesocket(sListen); WSACleanup(); return 0; } DWORD WINAPI WorkerThread(LPVOID lpParam) { int ret, index; DWORD cbTransferred; while (TRUE) { ret = WSAWaitForMultipleEvents(g_iTotalConn, g_CliEventArr, FALSE, 1000, FALSE); if (ret == WSA_WAIT_FAILED || ret == WSA_WAIT_TIMEOUT) { continue; } index = ret - WSA_WAIT_EVENT_0; WSAResetEvent(g_CliEventArr[index]); WSAGetOverlappedResult(g_CliSocketArr[index], &g_pPerIoDataArr[index]->overlap, &cbTransferred, TRUE, &g_pPerIoDataArr[g_iTotalConn]->Flags); if (cbTransferred == 0) { // The connection was closed by client Cleanup(index); } else { // g_pPerIoDataArr[index]->szMessage contains the recvived data g_pPerIoDataArr[index]->szMessage[cbTransferred] = '\0'; send(g_CliSocketArr[index], g_pPerIoDataArr[index]->szMessage, cbTransferred, 0); // Launch another asynchronous operation WSARecv(g_CliSocketArr[index], &g_pPerIoDataArr[index]->Buffer, 1, &g_pPerIoDataArr[index]->NumberOfBytesRecvd, &g_pPerIoDataArr[index]->Flags, &g_pPerIoDataArr[index]->overlap, NULL); } } return 0; } void Cleanup(int index) { closesocket(g_CliSocketArr[index]); WSACloseEvent(g_CliEventArr[index]); HeapFree(GetProcessHeap(), 0, g_pPerIoDataArr[index]); if (index < g_iTotalConn-1) { g_CliSocketArr[index] = g_CliSocketArr[g_iTotalConn-1]; g_CliEventArr[index] = g_CliEventArr[g_iTotalConn-1]; g_pPerIoDataArr[index] = g_pPerIoDataArr[g_iTotalConn-1]; } g_pPerIoDataArr[--g_iTotalConn] = NULL; }
这个模型与上述其他模型不同的是它使用Winsock2提供的异步I/O函数WSARecv。在调用WSARecv时,指定一个 WSAOVERLAPPED 结构,这个调用不是阻塞的,也就是说,它会立刻返回。一旦有数据到达的时候,被指定的WSAOVERLAPPED结构中的hEvent被 Signaled。由于下面这个语句
g_CliEventArr[g_iTotalConn] = g_pPerIODataArr[g_iTotalConn]->overlap.hEvent;
使得与该套接字相关联的WSAEVENT对象也被Signaled,所以WSAWaitForMultipleEvents的调用操作成功返回。我们现在应该做的就是用与调用WSARecv相同的WSAOVERLAPPED结构为参数调用WSAGetOverlappedResult,从而得到本次I/O 传送的字节数等相关信息。在取得接收的数据后,把数据原封不动的发送到客户端,然后重新激活一个WSARecv异步操作。
二、 用完成例程方式实现的重叠I/O 模型
// write by larry // 2009-8-20 // This is a server using overlapped IO(completion routine). #include "stdafx.h" #include <WINSOCK2.H> #include <stdio.h> #pragma comment(lib, "ws2_32.lib") #define PORT 5150 #define MSGSIZE 1024 typedef struct { WSAOVERLAPPED overlap; WSABUF Buffer; char szMessage[MSGSIZE]; DWORD NumberOfBytesRecvd; DWORD Flags; SOCKET sClient; } PER_IO_OPERATION_DATA, *LPPER_IO_OPERATION_DATA; int g_iTotalConn = 0; SOCKET g_CliSocketArr[MAXIMUM_WAIT_OBJECTS]; WSAEVENT g_CliEventArr[MAXIMUM_WAIT_OBJECTS]; LPPER_IO_OPERATION_DATA g_pPerIoDataArr[MAXIMUM_WAIT_OBJECTS]; DWORD WINAPI WorkerThread(LPVOID lpParam); void CALLBACK CompletionRoutine(DWORD dwError, DWORD cbTransferred, LPWSAOVERLAPPED lpOverlapped, DWORD dwFlags); SOCKET g_sNewClientConnection; BOOL g_bNewConnectionArrived = FALSE; int main(int argc, char* argv[]) { 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_family = AF_INET; local.sin_addr.S_un.S_addr = htonl(INADDR_ANY); local.sin_port = htons(PORT); bind(sListen, (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, (sockaddr*)&client, &iAddrSize); g_bNewConnectionArrived = TRUE; printf("Accepted client:%s:%d\n", inet_ntoa(client.sin_addr), ntohs(client.sin_port)); } return 0; } 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); } 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); } }
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。
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