blocking sockets timeout on receive issues - c++

Question

I'm writing a MFC\C++ program that needs to create a UDP socket to receive datagrams on.
I am using blocking socket (for performance reasons) and have some errors (or misunderstanding) when trying to set timeout for receive calls.
When I set the receive timeout to 100mili using setsockopt() and the receive does timeout - it timeouts after about 600mili.
When I set the receive timeout to 1000mili using setsockopt() and the receive does timeout - it timeouts after about 1600mili.
Why is this ?
Am I doing something wrong ?
My code goes something like this:
WSADATA wsaData;
SOCKET ReceivingSocket;
SOCKADDR_IN ReceiverAddr;
int Port = 2345;
char ReceiveBuf[1024];
int BufLength = 1024;
SOCKADDR_IN SenderAddr;
int SenderAddrSize = sizeof(SenderAddr);
int Ret;
// 100mili timeout
int RecvTimeout = 100 ;
// Initialize Winsock version 2.2
if ((Ret = WSAStartup(MAKEWORD(2,2), &wsaData)) != 0)
{
TRACE("ERROR: WSAStartup failed with error %d\n", Ret);
return;
}
// Create a new socket to receive datagrams
if ((ReceivingSocket = socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP))
== INVALID_SOCKET)
{
TRACE("ERROR: socket failed with error %d\n", WSAGetLastError());
WSACleanup();
return;
}
// receive datagrams from all interfaces using port 2345
ReceiverAddr.sin_family = AF_INET;
ReceiverAddr.sin_port = htons(Port);
ReceiverAddr.sin_addr.s_addr = htonl(INADDR_ANY);
// bind
if (bind(ReceivingSocket, (SOCKADDR *)&ReceiverAddr, sizeof(ReceiverAddr))
== SOCKET_ERROR)
{
TRACE("ERROR: bind failed with error %d\n", WSAGetLastError());
closesocket(ReceivingSocket);
WSACleanup();
return;
}
// set receive timeout
if ( setsockopt (
ReceivingSocket,
SOL_SOCKET,
SO_RCVTIMEO,
(const char*)&RecvTimeout,
sizeof(RecvTimeout) ) == SOCKET_ERROR )
{
TRACE("Error using setsockopt\n") ;
closesocket(ReceivingSocket);
WSACleanup();
return;
}
// Receive 10 messages - here the timeout comes to life...
for(int i = 0 ; i < 10 ; i++)
{
TRACE("Before Recv, Ticks=%d\n", GetTickCount()) ;
if ((Ret = recvfrom(ReceivingSocket, ReceiveBuf, BufLength, 0,
(SOCKADDR *)&SenderAddr, &SenderAddrSize)) == SOCKET_ERROR)
{
if(WSAETIMEDOUT == WSAGetLastError())
TRACE("After Recv, Ticks=%d\n\n", GetTickCount()) ;
else
{
TRACE("ERROR: receive failed with error %d\n", WSAGetLastError());
closesocket(ReceivingSocket);
WSACleanup();
return;
}
}
}
closesocket(ReceivingSocket);
WSACleanup();
and the output I get is this:
Before Recv, Ticks=1476485406
After Recv, Ticks=1476486031
Before Recv, Ticks=1476486031
After Recv, Ticks=1476486656
Before Recv, Ticks=1476486656
After Recv, Ticks=1476487281
.
.
.
In addition, when I looked at the MSDN to find out more about SO_RCVTIMEO I noticed the following:
If a send or receive operation times out on a socket, the socket state is indeterminate, and should not be used..."
So basically using SO_RCVTIMEO seems like a bad idea if I do get timeouts.
Am I missing something ?

Answer 1

Use 'timeval' stuct to initialize timeout value.
struct timeval timeout;
timeout.tv_sec = SOCKET_READ_TIMEOUT_SEC; // in milli secs
timeout.tv_usec = 0;