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重叠模型就是让应用程序使用重叠数据结构（WSAOVERLAPPED）,一次投递一个或者多个winsock i/0请求。针对这些请求，在他们完成之后，应用程序会收到通知，于是就可以用自己的代码来处理这些数据了。
有两个方法来管理重叠i/o请求的完成情况（就是说接到重叠操作完成的通知): 时间通知 和 完成例程。
基于事件通知：就是把windows事件和WSAOVERLAPPED结构关联在一起。使用WSASend, WSASendto,WSARecvFrom。可以把重叠结构与这些函数绑定在一起，提交请求，其他的事情就交给重叠结构去操心了。这样我们就可以坐享其成了，等到重叠结构完成之后，自然会有与之对应的事件来通知我们。我们根据重叠操作的结果取得我们需要的数据。
1。WSAOVERLAPPED
WSAEVENT event；
WSAOVERLAPPED AcceptOverlapped；
event = WSACreateEvent();
ZeroMemory(&Acceptoverlapped, sizeof(WSAOVERLAPPED));
AccepOverlapped.hEvent = event;
2. WSARecv系列函数

SOCKET S;
WSABUF DataBuf;
char buffer[5095];
ZeroMemorry(buffer,5095);
DataBuf.len = 5095;

DWORD dwBufferCount = 1, dwRecvBytes = 0, Flags = 0;
WSAOVERLAPPED AcceptOVerlapped;
WSAEVENT event;
event = WSACreateEvent();
ZeroMemory(&Acceptoverlapped, sizeof(WSAOVERLAPPED));
AcceptOverlapped.hEvent = event;

WSARecv(s, &DataBuf, dwBufferCount,&dwRecvBytes, &Flags, &AcceptOverlapped,NULL);

3.WSAWaitForMultipleEvents
等待事件的触发。

4.WSAGetOverlappedResult
查询重叠操作的结果。

[1] 定义变量
#define DATA_BUFSIZE 4096

SOCKET ListenSocket;//监听套节字
Socket AcceptSocket;//与客户端通信的套节字
WSAOVERLAPPED AcceptOverlapped;//重叠结构
WSAEVENT EventArray[WSA_MAXIMUM_WAIT_EVENTS];//用来通知重叠操作完成的事件句柄数组
WSABUF DataBuf[WSA_MAXIMUM_WAIT_EVENTS];
DWORD dwEventTotal = 0;//事件总数
DWORD dwRecvBytes = 0;//接收的字符长度
Flags= 0 ；
[2] 创建套节字并在指定的端口上监听连接请求。
WSADATA wsaData;
WSAStartup();

ListenSocket = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);

SOCKADDR_IN ServerAddr;
serverAddr.sin.family = AF_INET;
serverAddr.sin.addr.S_un.S_addr = htonl(INNADDR_ANY);
serverAddr.sin_port = htons(11111);

bind(ListenSocket, &serveraddr, sizeof());

listen(Listensocket,5);
[3] 接收一个入站的连接请求。
SOCKADDR_IN clientAddr;
int addr_length = sizeof(clientAddr);
AcceptSocket= accept(ListenSocket, &clientsocket, &addr_length);
LPCTSTR lpIP = inet_ntoa(clientAddr.sin_addr);//client ip
UINT nPort = clientAddr.sin_port;//client port

[4]建立并初始化重叠结构

EventArray[dwEventTotal] = WSACreateEvent;
ZeroMemory(&Acceptoverlapped, sizeof(WSAOVERLAPPED));
AcceptOverlapped.hEvent = EventArray[dwEventTotal];//关联事件

char buffer[DATA_BUFSIZE];
ZeroMemory(buffer, DATA_BUFSIZE);

DataBuffer.len = DATA_BUFFER;//初始化一个WSABUF结构
DataBuffer.buf = buffer;

dwEventTotal++;
[5] 以WSAOVERLAPPED为参数，在套节字上投递WSARecv请求。