参考
《TCP/IP网络编程》 尹圣雨重叠I/O模型
理解重叠I/O模型
同一线程内部向多个目标传输（或从多个目标接收）数据引起的I/O重叠现象称为“重叠I/O”。为了完成这项任务，调用的I/O函数应立即返回，因此前提条件是异步I/O。而且，为了完成异步I/O，调用的I/O函数应以非阻塞模式工作
Windows中重叠I/O的重点并非I/O本身，而是如何确认I/O完成时的状态
创建重叠I/O套接字
#include <winsock2.h>SOCKET WSASocket(int af, int type, int protocol, LPWSAPROTOCOL_INFO lpProtocolInfo, GROUP g, DWORD dwFlags);
成功时返回套接字句柄，失败时返回INVALID_SOCKET。其中：
af：协议族信息type：套接字数据传输方式protocol：2个套接字之间使用的协议信息lpProtocolInfo：包含创建的套接字信息的WSAPROTOCOL_INFO结构体变量地址值，不需要时传递NULLg：为扩展函数而预约的参数，可以使用0dwFlags：套接字属性信息
可以向最后一个参数传递WSA_FLAG_OVERLAPPED，赋予创建出的套接字重叠I/O特性。例如：
WSASocket(PF_INET, SOCK_STREAM, 0, NULL, 0, WSA_FLAG_OVERLAPPED);
执行重叠I/O的函数
重叠I/O模型中，服务器端和客户端间的连接过程与一般的套接字连接过程相同，但I/O数据时使用的函数不同
WSASend
#include <winsock2.h>int WSASend(SOCKET s, LPWSABUF lpBuffers, DWORD dwBufferCount, LPDWORD lpNumberOfBytesSent, DWORD dwFlags, LPWSAOVERLAPPED lpOverlapped, LPWSAOVERLAPPED_COMPLETION_ROUTINE lpCompletionRoutine);
成功时返回0，失败时返回SOCKET_ERROR。其中：
s：套接字句柄，传递具有重叠I/O属性的套接字句柄时，以重叠I/O模型输出lpBuffers：WSABUF结构体变量数组的地址值，WSABUF中存有待传输数据dwBufferCount：第二个参数中数组的长度lpNumberOfBytesSent：用于保存实际发送字节数的变量地址值dwFlags：用于更改数据传输特性，如传递MSG_OOB时发送OOB模式的数据lpOverlapped：WSAOVERLAPPED结构体变量的地址值，使用事件对象，用于确认完成数据传输lpCompletionRoutine：传入Completion Routine函数的入口地址值，可以通过该函数确认是否完成数据传输
WSABUF结构体
WSASend第二个参数涉及的WSABUF结构体中存有待传输数据的地址和大小等信息：
typedef struct __WSABUF{u_long len; // 待传输数据的大小char FAR* buf;// 缓冲地址值}WSABUF, * LPWSABUF;
WSAOVERLAPPED结构体
WSASend第六个参数涉及的WSAOVERLAPPED结构体定义如下：
typedef struct __WSAOVERLAPPED{DWORD Internal;DWORD InternalHigh;DWORD Offset;DWORD OffsetHigh;WSAEVENT hEvent;}WSAOVERLAPPED, * LPWSAOVERLAPPED;
其中，Internal、InternalHigh成员是进行重叠I/O时操作系统内部使用的成员，而Offset、OffsetHigh属于具有特殊用途的成员。此处只需关注hEvent成员
WSASend函数的lpOverlapped参数中应传递有效的结构体变量地址值，如果传递NULL，WSASend函数的第一个参数中的句柄所指的套接字将以阻塞模式工作。另外，利用WSASend函数同时向多个目标传递数据时，需要分别构建传入第六个参数的WSAOVERLAPPED结构体变量
WSASend示例
WSAEVENT event;WSAOVERLAPPED overlapped;WSABUF dataBuf;char buf[BUF_SIZE] = {"待传输的数据"};int recvBytes = 0;......event = WSACreateEvent();memset(&overlapped, 0, sizeof(overlapped));overlapped.hEvent = event;dataBuf.len = sizeof(buf);dataBuf.buf = buf;WSASend(hSocket, &dataBuf, 1, &recvBytes, 0, &overlapped, NULL);......
获取实际传输数据大小
WSASend函数调用过程中，如果输出缓冲是空的，且传输的数据并不大，那么函数调用后可以立即完成数据传输。此时WSASend函数将返回0，而lpNumberOfBytesSent中将保存实际传输的数据大小的信息。反之，WSASend函数返回后仍需要传输数据时，将返回SOCKET_ERROR，并将WSA_IO_PENDING注册为错误代码，该代码可以通过WSAGetLastError函数得到。这时使用WSAGetOverlappedResult函数获取实际传输的数据大小
#include <winsock2.h>BOOL WSAGetOverlappedResult(SOCKET s, LPWSAOVERLAPPED lpOverlapped, LPDWORD lpcbTransfer, BOOL fWait, LPDWORD lpdwFlags);
成功时返回TRUE，失败时返回FALSE。其中：
s：进行重叠I/O的套接字句柄lpOverlapped：进行重叠I/O时传递的WSAOVERLAPPED结构体变量的地址值lpcbTransfer：用于保存实际传输的字节数的变量地址值fWait：如果调用该函数时仍在进行I/O，fWait为TRUE时等待I/O完成，fWait为FALSE时将返回FALSE并跳出函数lpdwFlags：调用WSARecv函数时，用于获取附加信息（例如OOB消息）。如果不需要，可以传递NULL
WSARecv
#include <winsock2.h>int WSARecv(SOCKET s, LPWSABUF lpBuffers, DWORD dwBufferCount, LPDWORD lpNumberOfBytesRecvd, LPWORD lpFlags, LPWSAOVERLAPPED lpOverlapped, LPWSAOVERLAPPED_COMPLETION_ROUTINE lpCompletionRoutine);
成功时返回0，失败时返回SOCKET_ERROR。其中：
s：赋予重叠I/O属性的套接字句柄lpBuffers：用于保存接收数据的WSABUF结构体数组地址值dwBufferCount：向第二个参数传递的数组的长度lpNumberOfBytesRecvd：保存接收的数据大小信息的变量地址值lpFlags：用于设置或读取传输特性信息lpOverlapped：WSAOVERLAPPED结构体变量地址值lpCompletionRoutine：Completion Routine函数地址值
确认重叠I/O的I/O完成
重叠I/O中有2种方法确认I/O的完成并获取结果：
利用WSASend、WSARecv函数的第六个参数，基于事件对象利用WSASend、WSARecv函数的第七个参数，基于Completion Routine
使用事件对象
Sender
#include <stdio.h>#include <stdlib.h>#include <WinSock2.h>#include <WS2tcpip.h>void ErrorHandling(char* msg);int main(int argc, char* argv[]){WSADATA wsaData;SOCKET hSocket;SOCKADDR_IN sendAdr;WSABUF dataBuf;char msg[] = "Network is Computer!";int sendBytes = 0;WSAEVENT evObj;WSAOVERLAPPED overlapped;if (argc != 3){printf("Usage : %s <IP> <port>\n", argv[0]);exit(1);}if (WSAStartup(MAKEWORD(2, 2), &wsaData) != 0){ErrorHandling("WSAStartup() error!");}hSocket = WSASocket(PF_INET, SOCK_STREAM, 0, NULL, 0, WSA_FLAG_OVERLAPPED);memset(&sendAdr, 0, sizeof(sendAdr));sendAdr.sin_family = AF_INET;inet_pton(AF_INET, argv[1], &sendAdr.sin_addr);sendAdr.sin_port = htons(atoi(argv[2]));if (connect(hSocket, (SOCKADDR*)&sendAdr, sizeof(sendAdr)) == SOCKET_ERROR){ErrorHandling("connnect() error!");}evObj = WSACreateEvent();memset(&overlapped, 0, sizeof(overlapped));overlapped.hEvent = evObj;dataBuf.len = strlen(msg) + 1;dataBuf.buf = msg;if (WSASend(hSocket, &dataBuf, 1, &sendBytes, 0, &overlapped, NULL) == SOCKET_ERROR){if (WSAGetLastError() == WSA_IO_PENDING){puts("Background data send");WSAWaitForMultipleEvents(1, &evObj, TRUE, WSA_INFINITE, FALSE); // 完成I/O时，evObj将变为signaled，函数返回WSAGetOverlappedResult(hSocket, &overlapped, &sendBytes, FALSE, NULL);}else{ErrorHandling("WSASend() error");}}printf("Send data size: %d \n", sendBytes);WSACloseEvent(evObj);closesocket(hSocket);WSACleanup();return 0;}void ErrorHandling(char* msg){fputs(msg, stderr);fputc('\n', stderr);exit(1);}
Receiver
#include <stdio.h>#include <stdlib.h>#include <WinSock2.h>#define BUF_SIZE 1024void ErrorHandling(char* message);int main(int argc, char* argv[]){WSADATA wsaData;SOCKET hLisnSock, hRecvSock;SOCKADDR_IN lisnAdr, recvAdr;int recvAdrSz;WSABUF dataBuf;WSAEVENT evObj;WSAOVERLAPPED overlapped;char buf[BUF_SIZE];int recvBytes = 0, flags = 0;if (argc != 2){printf("Usage : %s <port>\n", argv[0]);exit(1);}if (WSAStartup(MAKEWORD(2, 2), &wsaData) != 0){ErrorHandling("WSAStartup() error!");}hLisnSock = WSASocket(PF_INET, SOCK_STREAM, 0, NULL, 0, WSA_FLAG_OVERLAPPED);memset(&lisnAdr, 0, sizeof(lisnAdr));lisnAdr.sin_family = AF_INET;lisnAdr.sin_addr.s_addr = htonl(INADDR_ANY);lisnAdr.sin_port = htons(atoi(argv[1]));if (bind(hLisnSock, (SOCKADDR*)&lisnAdr, sizeof(lisnAdr)) == SOCKET_ERROR){ErrorHandling("bind() error");}if (listen(hLisnSock, 5) == SOCKET_ERROR){ErrorHandling("listen() error");}recvAdrSz = sizeof(recvAdr);hRecvSock = accept(hLisnSock, (SOCKADDR*)&recvAdr, &recvAdrSz);evObj = WSACreateEvent();memset(&overlapped, 0, sizeof(overlapped));overlapped.hEvent = evObj;dataBuf.len = BUF_SIZE;dataBuf.buf = buf;if (WSARecv(hRecvSock, &dataBuf, 1, &recvBytes, &flags, &overlapped, NULL) == SOCKET_ERROR){if (WSAGetLastError() == WSA_IO_PENDING){puts("Background data receive");WSAWaitForMultipleEvents(1, &evObj, TRUE, WSA_INFINITE, FALSE);WSAGetOverlappedResult(hRecvSock, &overlapped, &recvBytes, FALSE, NULL);}else{ErrorHandling("WSARecv() error");}}printf("Received message: %s \n", buf);WSACloseEvent(evObj);closesocket(hRecvSock);closesocket(hLisnSock);WSACleanup();return 0;}void ErrorHandling(char* message){fputs(message, stderr);fputc('\n', stderr);exit(1);}
使用Completion Routine函数
通过WSASend、WSARecv函数的最后一个参数中指定的Completion Routine（CR）函数验证I/O完成情况
I/O完成时调用注册的CR函数进行事后处理。操作系统通常会预先定义规则，只有请求I/O的线程处于alertable wait状态时才能调用Completion Routine函数，防止破坏程序正常执行流
启动I/O任务后，执行完紧急任务时可以调用下面任一函数验证I/O完成与否：
WaitForSingObjectExWaitForMultipleObjectWSAWaitForMultipleEventsSleepEx
这些函数都有1个参数fAlertable，如果该参数为TRUE，则相应线程进入alertable wait状态，如果有已完成的I/O，则调用相应CR函数。调用后，这些函数都返回WAIT_IO_COMPLETION
CR函数原型：
void CALLBACK CompletionROUTINE(DWORD dwError, DWORD cbTransferred, LPWSAOVERLAPPED lpOverlapped, DWORD dwFlags);
其中：
dwError：写入错误信息（正常结束时写入0）cbTransferred：写入实际收发的字节数lpOverlapped：写入WSASend、WSARecv函数的参数lpOverlappeddwFlags：写入调用I/O函数时传入的特性信息或0CALLBACK：与WINAPI相同，都是用于声明函数的调用规范，必须添加
Receiver
#include <stdio.h>#include <stdlib.h>#include <WinSock2.h>#define BUF_SIZE 1024void CALLBACK CompRoutine(DWORD, DWORD, LPWSAOVERLAPPED, DWORD);void ErrorHandling(char* message);WSABUF dataBuf;char buf[BUF_SIZE];int recvBytes = 0;int main(int argc, char* argv[]){WSADATA wsaData;SOCKET hLisnSock, hRecvSock;SOCKADDR_IN lisnAdr, recvAdr;WSAOVERLAPPED overlapped;WSAEVENT evObj;int idx, recvAdrSz, flags = 0;if (argc != 2){printf("Usage : %s <port>\n", argv[0]);exit(1);}if (WSAStartup(MAKEWORD(2, 2), &wsaData) != 0){ErrorHandling("WSAStartup() error!");}hLisnSock = WSASocket(PF_INET, SOCK_STREAM, 0, NULL, 0, WSA_FLAG_OVERLAPPED);memset(&lisnAdr, 0, sizeof(lisnAdr));lisnAdr.sin_family = AF_INET;lisnAdr.sin_addr.s_addr = htonl(INADDR_ANY);lisnAdr.sin_port = htons(atoi(argv[1]));if (bind(hLisnSock, (SOCKADDR*)&lisnAdr, sizeof(lisnAdr)) == SOCKET_ERROR){ErrorHandling("bind() error");}if (listen(hLisnSock, 5) == SOCKET_ERROR){ErrorHandling("listen() error");}recvAdrSz = sizeof(recvAdr);hRecvSock = accept(hLisnSock, (SOCKADDR*)&recvAdr, &recvAdrSz);if (hRecvSock == INVALID_SOCKET){ErrorHandling("accept() error");}memset(&overlapped, 0, sizeof(overlapped));dataBuf.len = BUF_SIZE;dataBuf.buf = buf;evObj = WSACreateEvent();if (WSARecv(hRecvSock, &dataBuf, 1, &recvBytes, &flags, &overlapped, CompRoutine) == SOCKET_ERROR) // 必须指定第六个参数WSAOVERLAPPED结构体变量的地址值，但不必为了hEvent成员创建事件对象{if (WSAGetLastError() == WSA_IO_PENDING){puts("Background data receive");}}idx = WSAWaitForMultipleEvents(1, &evObj, FALSE, WSA_INFINITE, TRUE);// 使main进程进入alertable wait状态。为此，创建了多余的事件对象evObjif (idx == WAIT_IO_COMPLETION) // I/O正常结束{puts("Overlapped I/O Completed");}else{ErrorHandling("WSARecv() error");}WSACloseEvent(evObj);closesocket(hRecvSock);closesocket(hLisnSock);WSACleanup();return 0;}void CALLBACK CompRoutine(DWORD dwError, DWORD szRecvBytes, LPWSAOVERLAPPED lpOverlapped, DWORD flags){if (dwError != 0){ErrorHandling("CompRoutine error");}else{recvBytes = szRecvBytes;printf("Received message: %s \n", buf);}}void ErrorHandling(char* message){fputs(message, stderr);fputc('\n', stderr);exit(1);}
