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8.2.4 重叠模型
s = WSASocket(AF_INET, SOCK_STREAM, 0, NULL, 0, WSA_FLAG_OVERLAPPED);
1.事件通知 将win32事件对象与WSAOVERLAPPED结构关联在一起。
typedef struct WSAOVERLAPPED
{
DWORD Internal;
DWORD InternalHigh;
DWORD offset;
DWORD OffsetHigh;
WSAEVENT hEvent;
} WSAOVERLAPPED, FAR*LPWSAOVERLAPPED;
hEvent 它允许应用程序将一个事件对象句柄同一个套接字关联起来。

BOOL WSAGetOverlappedResult(SOCKET S, LPWSAOVERLAPPED lpOverlapped, LPDWORD lpcbTransfer, BOOL fWari, LPDWORD lpdwFlags);
void main()
{
WSABUF DataBuf;
DWORD EventTotal = 0;
WSAEVENT EventArray[WSA_MAXIMUM_WAIT_EVENTS];
WSAOVERLAPPED AcceptOverlapped;
SOCKET ListenSocket, AcceptSocket;

//step 1
//start winsock and set up a listening socket

//step 2
//accepte an inbound connection

AcceptSocket = accept(ListenSocket, NULL, NULL);

//step 3
//set up an overlapped structure

EventArray[EventTotal]=WSACreateEvent();
ZeroMemory(&AcceptOverlapped, sizeof(WSAOVERLAPPED));

AcceptOverlapped.hEvent = EventArray[EventTotal];

DataBuf.len = DATA_BUFSIZE;
DataBuf.buf = buffer;

EventTotal++;

//step 4;
//post a WSARecv request to begin receiving data on the socket.
WSARecv(AcceptSocket, &DataBuf, 1, &RecvBytes, &Flags, &AcceptOverlapped, NULL);

//Process overlapped receives on the socket.
while (TRUE)
{
//step 5
//wait for overlapped io call to complete
Index = WSAWaitForMultipleEvents(EventTotal, EventArray, FALSE, WSA_INFINITE, FALSE);

//Index should be 0 because we have one event handle in eventarray.

//step 6
//reset the signaled event
WSAResetEvent(EventArray[Index - WSA_WAIT_EVENT_0]);

//step 7
//Determine the status of the overlapped request.
WSAGetOverlappedResult(AcceptSocket, &AcceptOverlapped, &BytesTransferred, FALSE, &Flags);

//First check to see whether the peer has closed the connection ,and if so , close the socket.
if (BytesTransferred == 0)
{
printf("Closing socket %d\n", AcceptSocket);
closesocket(AcceptSocket);
WSACloseEvent(Index - WSA_WAIT_EVENT_0);
return;
}

//Do something with the received data DataBuf contains the received data.
...

//step 8
//post another WSARecv() request on the socket

Flags = 0;
ZeroMemory(&AcceptOverlapped, sizeof(WSAOVERLAPPED));

AcceptOverlapped.hEvent = EventArray[Index - WSA_WAIT_EVENT_0];

DataBuf.len = DATA_BUFSIZE;
DataBuf.buf = Buffer;

WSARecv(AcceptSocket, &DataBuf, 1, &RecvBytes, &Flags, &AcceptOverlapped, NULL);
}
}

2.完成例程
在一个重叠IO请求完成时由系统调用的函数。他们的基本设计宗旨是通过调用者的线程，为一个已完成的I请求提供服务。除此之外，应用程序可通过完成例程，继续进行重叠IO处理。
void CALLBACK CompletionROUTINE(DWORD dwError, DWORD cbTransferred, LPWSAOVERLAPPED lpOverlapped, DWORD dwFlags);

WSABUF DataBuf;
SOCKET AcceptSocket;

void main()
{
WSAOVERLAPPED Overlapped;

//step 1
//start winsock and set up a listening socket

//step 2
//accept a new connection
AcceptSocket = accept(ListenSocket, NULL, NULL);

//step 3
//To get the overlapped IO processing started, first submit an overlapped WSARecv() request.

Flags = 0;
ZeroMemory(&Overlapped, sizeof(WSAOVERLAPPED));

DataBuf.len = DATA_BUFSIZE;
DataBuf.buf = buffer;

EventTotal++;

//step 4;
//post a WSARecv request to begin receiving data on the socket.
if(WSARecv(AcceptSocket, &DataBuf, 1, &RecvBytes, &Flags, &AcceptOverlapped, WorkerRoutine)==SOCKET_ERROR)
{
if (WSAGetLastError()!=WSA_IO_PENDING)
{
printf("WSARecv() failed with error%d\n",WSAGetLastError());
return;
}
}

//since the WSAWaitForMutipleEvents()API requires waiting on one or more event objects, we will have to create a dummy event object, Aa
//an alterative , we can use SleepEx() instead.
EventArray[0]=WSACreateEvent();

while (TRUE)
{
//step 5
Index = WSAWaitForMultipleEvents(1,EventArray, FALSE, WSA_INFINITE, FALSE);

//step 6
if (Index == WAIT_IO_COMPLETION)
{
//An overlapped request completion routine just completed ,continue servicing more completion rountines.
}
else
{
//A bad error occurred --stop processing! if we were also processing an event object, this could be index to the event array.

return;
}
}
}

void CALLBACK WorkerRoutine(DWORD Error, DWORD BytesTransferred, LPWSAOVERLAPPED Overlapped, DWORD InFlags)
{
DWORD SendBytes, RecvBytes;
DWORD Flags;
if (Error !=0)||BytesTransferred ==0
{
//Either a bad error occurred on the socket or the socket was closed by peer closesocket(AcceptSocket);
return;
}

//At this point, an overlapped WSARecv() request completed successfully. Now we can retrieve the received data that is contained in the variable DataBuf
//After processing the received data, we need to post another overlapped WSARecv() or WSASend() request. For simplicity , we will post another WSARecv() requst.
Flags = 0;
ZeroMemory(&Overlapped,sizeof(WSAOVERLAPPED));

DataBuf.len = DATA_BUFSIZE;
DataBuf.buf = Buffer;

if (WSARecv(AcceptSocket, &DataBuf,1,&RecvBytes,&Flags, &Overlapped, WorkerRoutine)==SOCKET_ERROR)
{
if (WSAGetLastError()!=WSA_IO_PENDING)
{
printf("failed with error%d\n",WSAGetLastError());
return;
}
}
}