Problem with wsarecv while using with IOCP - iocp

Question

I am new to IOCP and struggling with this for last few weeks.
I have pasted some core part of my code below related to IOCP.This may not be executed perfectly as I clipped some part to make it easy to understand.
I am struggling while receiving the data.As it comes to wsarecv in worket thread, wsarecv returns WSA_IO_PENDING error code so I call WSAGetOverlappedResult to check operation to be completed.
Twist comes here, rather it proceed and call my local function ProcessTelegramData after WSAGetOverlappedResult , same part of code(wsarecv called again) is executed again by another worker thread which try to call ProcessTelegramData and buffer value is invalid in it.
I am unable to understand
why another thread calling wsarecv again when WSAGetOverlappedResult is called and
why buffer value is getting invalidated?
unsigned LicTCPServer::WorkerThread(LPVOID lpParam)
{
//int nThreadNo = (int)lpParam;
LicTCPServer* pThis = reinterpret_cast<LicTCPServer*>(lpParam);
void *lpContext = NULL;
OVERLAPPED *pOverlapped = NULL;
CClientContext *pClientContext = NULL;
DWORD dwBytesTransfered = 0;
int nBytesRecv = 0;
int nBytesSent = 0;
DWORD dwBytes = 0, dwFlags = 0;
//Worker thread will be around to process requests, until a Shutdown event is not Signaled.
while (WAIT_OBJECT_0 != WaitForSingleObject(g_hShutdownEvent, 0))
{
BOOL bReturn = GetQueuedCompletionStatus(
g_hIOCompletionPort,
&dwBytesTransfered,
(LPDWORD)&lpContext,
&pOverlapped,
INFINITE);
if (NULL == lpContext)
{
//We are shutting down
break;
}
//Get the client context
pClientContext = (CClientContext *)lpContext;
if ((FALSE == bReturn) /*|| ((TRUE == bReturn) && (0 == dwBytesTransfered))*/)
{
//Client connection gone, remove it.
pThis->RemoveFromClientListAndFreeMemory(pClientContext);
continue;
}
WSABUF *p_wbuf = pClientContext->GetWSABUFPtr();
OVERLAPPED *p_ol = pClientContext->GetOVERLAPPEDPtr();
//printf("reached %d\n",pClientContext->GetOpCode());
printf("Get Queued received\n");
switch (pClientContext->GetOpCode())
{
case OP_READ:
{
//Once the data is successfully received, we will print it.
//pClientContext->SetOpCode(OP_WRITE);
pClientContext->ResetWSABUF();
dwFlags = 0;
//int a = recv(pClientContext->GetSocket(), p_wbuf->buf, p_wbuf->len, 0);
//Get the data.
if(WSARecv(pClientContext->GetSocket(), p_wbuf, 1, &dwBytes, &dwFlags, p_ol, NULL) == SOCKET_ERROR)
{
if (WSAGetLastError() != WSA_IO_PENDING)
{
printf("Error occured at WSARecv()\n");
return 0;
}
}
DWORD byteTr = 0;
WSAGetOverlappedResult(pClientContext->GetSocket(),p_ol,&byteTr,TRUE,&dwFlags);
if( byteTr > 0 )
{
//doing some operatin on data received
printf("Process tele called\n");
g_pLicServFunc->ProcessTelegramData(pClientContext->GetSocket(), p_wbuf->buf, byteTr);
}
if ((SOCKET_ERROR == nBytesRecv) && (WSA_IO_PENDING != WSAGetLastError()))
{
//WriteToConsole("\nThread %d: Error occurred while executing WSARecv().", nThreadNo);
//Let's not work with this client
//TBC
//RemoveFromClientListAndFreeMemory(pClientContext);
}
}
break;
case OP_WRITE:
char szBuffer[MAX_BUFFER_LEN];
//Send the message back to the client.
pClientContext->SetOpCode(OP_READ);
pClientContext->SetTotalBytes(dwBytesTransfered);
pClientContext->SetSentBytes(0);
//p_wbuf->len = dwBytesTransfered;
dwFlags = 0;
DWORD temp;
//Overlapped send
printf("reached Going to send\n");
//send(pClientContext->GetSocket(), p_wbuf->buf,p_wbuf->len, 0);
nBytesSent = WSASend(pClientContext->GetSocket(), p_wbuf, 1,
&temp, dwFlags, p_ol, NULL);
if ((SOCKET_ERROR == nBytesSent) && (WSA_IO_PENDING != WSAGetLastError()))
{
//WriteToConsole("\nThread %d: Error occurred while executing WSASend().", nThreadNo);
//Let's not work with this client
//TBC
//RemoveFromClientListAndFreeMemory(pClientContext);
}
break;
default:
printf("reached to default\n");
//We should never be reaching here, under normal circumstances.
break;
} // switch
} // while
return 0;
}

Answer 1

I had a similar issue with WSARecv where it always queued to the io completion queue, even if it succeeded immediately. I had to ignore a return value indicating success and instead handle the queued result that I got from GetQueuedCompletionStatus.