Re: Please Help!!! - CAsyncSocket::OnReceive Not Working for Microsoft UDP Application (msocudp)

"Alexander Nickolov" <>
Wed, 21 May 2008 12:32:17 -0700
Your biggest problem is calling Sleep and WaitForSingleObject
on your UDP thread (all other problems are secondary). You
have to instead run a message loop by returning from InitInstance
(IIRC CWinThread does this for you automatically).

I suspect you shouldn't use CAsyncSocket in the first place.
Use a regular WinSock socket (without MFC!) in blocking
(or non-bocking) mode instead.

Note that your requirement to receive all packets means you
need to either switch to the TCP protocol (which is reliable) or
implement some reliability within your own protocol in order
to request missing packets be resent by the sender.

Alexander Nickolov
Microsoft MVP [VC], MCSD

"Roshan" <> wrote in message
On May 20, 12:31 pm, "Scott McPhillips [MVP]" <org-dot-mvps-at-
scottmcp> wrote:

"Roshan" <> wrote in message

The result I am currently getting from running my code is that: I am
sending the packet and 10 result packets are being sent back, but
OnReceive is not getting invoked at all which leads to my program
hanging at the WaitForSingleObject() calls.

I pointed out serious design errors in your code. You did not address or
correct any of them. OnReceive will not be invoked until you do correct

Scott McPhillips [VC++ MVP]


I have created a CWinThread derived class. I have been trying to
follow some examples from the web.
I am trying to pass the socket from my dialog class to my thread
class. One problem I am having now when running the code is that it is
failing when I am attaching the socket handle to the socket object in
the InitInstance() function of my thread class.
The error I'm getting is access violation. Others seemed to have
gotten this error before. How do you fix this?

Code Snippets:

CProdTestUdpThread (My CWinThread derived class)

BOOL CProdTestUdpThread::InitInstance()
// TODO: perform and per-thread initialization here
m_UDPSocket.Attach(m_hSocket); (*** THIS IS WHERE THE ERROR

m_UDPSocket.m_nBytesSent = 0;
m_UDPSocket.m_sendBuffer = m_sendString;
m_UDPSocket.m_nBytesBufferSize = m_sendString.GetLength() + 1;



WaitForSingleObject(m_hRcvEvent, INFINITE);


return TRUE;

CProdTestDlg (Normal Function definition in my dialog source file --

void CProdTestDlg::NormalFunction(int hexNum)
CString sendString, verString = "01", seqString, twoByteHexAddInfo;
m_cmdString = "02";

twoByteHexAddInfo.Format("%04x", hexNum);
seqString.Format("%02x", m_pUDPSocket->m_sequenceNumber);
sendString = verString + seqString + m_cmdString + twoByteHexAddInfo;

CProdTestUdpThread *pThread =
(CProdTestUdpThread *) AfxBeginThread(

// Pass the socket to the thread by passing the socket handle.
// You cannot pass a CSocket object across threads.
pThread->m_hSocket = m_pUDPSocket->Detach();
pThread->m_sendString = sendString;
pThread->m_delay = 10;
m_pUDPSocket->m_pRcvEvent = &(pThread->m_hRcvEvent);

                // Now start the thread.

WaitForSingleObject(pThread->m_hThread, INFINITE);

MICROSOFT's UDP OnReceive() Function (Instead of the class being
named, CUdpAsySk, I changed it to CProdTestUdpSk).

void CProdTestUdpSk::OnReceive(int nErrorCode)

SetEvent(*m_pRcvEvent); // *** NOTIFY THREAD CLASS WHEN ALL 10
                                                            // PACKETS


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