Question

I am writing a Windows 7 visual c++ server application, which should receive UDP datagrams with 3.6 MB/s.
I have a main thread where the recvfrom() receives the data. The socket is a non-blocking socket and has 64kB receive buffer. If no data has been received on the socket the thread executes a sleep(1).

My problem is that the thread uses up almost 50% of my dual-core processor and I have no idea how could I decrease it. Wireshark use only 20% of it, so my main goal is to achieve a similar percentage.

Do you have any ideas?

Answer 1

Rather than polling you could use a select-like approach to wait for either data to arrive at your socket or the client to decide to shutdown:

First make your socket non-blocking:

u_long nonBlocking = 0;
WSAEventSelect(sock, NULL, 0);
ioctlsocket(sock, FIONBIO, &nonBlocking);

then use WSAWaitForMultipleEvents to wait until either data arrives or you want to cancel the recv:

int32_t MyRecv(THandle sock, WSAEVENT* recvCancelEvt,
               uint8_t* buffer, uint32_t bufferBytes)
{
    int32_t bytesReceived;
    WSAEVENT evt;
    DWORD ret;
    HANDLE handles[2];

    event = WSACreateEvent();
    if (NULL == evt) {
        return -1;
    }
    if (0 != WSAEventSelect(handle->iSocket, evt, FD_READ|FD_CLOSE)) {
        WSACloseEvent(evt);
        return -1;
    }

    bytesReceived = recv(sock, (char*)buffer, bufferBytes, 0);
    if (SOCKET_ERROR==received && WSAEWOULDBLOCK==WSAGetLastError()) {
        handles[0] = evt;
        handles[1] = *recvCancelEvt;
        ret = WSAWaitForMultipleEvents(2, handles, FALSE, INFINITE, FALSE);
        if (WAIT_OBJECT_0 == ret) {
            bytesReceived = recv(handle->iSocket, (char*)buffer, bufferBytes, 0);
        }
    }
    WSACloseEvent(evt);
    return bytesReceived;
}

Client code would call WSASetEvent on recvCancelEvt if it wanted to cancel a recv.