Windows message loop and server loop - c++

Question

I made a window using the Win32 API and it needs to enter a message loop:
while (GetMessage(&msg, nullptr, 0, 0))
{
TranslateMessage(&msg);
DispatchMessage(&msg);
}
How do I create a socket server and start receiving clients, if my main thread is processing UI messages?
I tried putting all of the server code in a thread using CreateThread() from WinMain(), but it just crashes with an error:
Exception thrown at 0x00000000 in test.exe: 0xC0000005: Access violation executing location 0x00000000.
Here is the thread code:
DWORD WINAPI ThreadProc(LPVOID lpParameter)
{
// Initialize Winsock
WSADATA wsaData;
auto iResult = WSAStartup(MAKEWORD(2, 2), &wsaData);
if (iResult != 0) {
printf("WSAStartup failed with error: %d\n", iResult);
return EXIT_FAILURE;
}
addrinfo hints;
ZeroMemory(&hints, sizeof(hints));
hints.ai_family = AF_INET;
hints.ai_socktype = SOCK_STREAM;
hints.ai_protocol = IPPROTO_TCP;
hints.ai_flags = AI_PASSIVE;
// Resolve the server address and port
PADDRINFOA pAddrInfo = nullptr;
iResult = getaddrinfo(nullptr, PORT, &hints, &pAddrInfo);
if (iResult != 0) {
printf("getaddrinfo failed with error: %d\n", iResult);
WSACleanup();
return EXIT_FAILURE;
}
while (true) {
// Create a SOCKET for connecting to server
auto ListenSocket = socket(pAddrInfo->ai_family, pAddrInfo->ai_socktype, pAddrInfo->ai_protocol);
if (ListenSocket == INVALID_SOCKET) {
printf("socket failed with error: %ld\n", WSAGetLastError());
freeaddrinfo(pAddrInfo);
WSACleanup();
return EXIT_FAILURE;
}
// Setup the TCP listening socket
iResult = bind(ListenSocket, pAddrInfo->ai_addr, static_cast<int>(pAddrInfo->ai_addrlen));
if (iResult == SOCKET_ERROR) {
printf("bind failed with error: %d\n", WSAGetLastError());
freeaddrinfo(pAddrInfo);
closesocket(ListenSocket);
WSACleanup();
return EXIT_FAILURE;
}
freeaddrinfo(pAddrInfo);
iResult = listen(ListenSocket, SOMAXCONN);
if (iResult == SOCKET_ERROR) {
printf("listen failed with error: %d\n", WSAGetLastError());
closesocket(ListenSocket);
WSACleanup();
return EXIT_FAILURE;
}
// Accept a client socket
auto ClientSocket = accept(ListenSocket, nullptr, nullptr);
if (ClientSocket == INVALID_SOCKET) {
printf("accept failed with error: %d\n", WSAGetLastError());
closesocket(ListenSocket);
WSACleanup();
return EXIT_FAILURE;
}
// No longer need server socket
closesocket(ListenSocket);
// Receive until the peer shuts down the connection
for (;;)
{
char recvbuf[1] = { 0 };
auto cbLen = recv(ClientSocket, recvbuf, sizeof(recvbuf), 0);
if (cbLen > 0) {
if (recvbuf[0] == 0xDA)
{
Hide();
}
continue;
}
else if (cbLen == 0) {
printf("Connection closing...\n");
break;
}
else {
printf("recv failed with error: %d\n", WSAGetLastError());
closesocket(ClientSocket);
WSACleanup();
return EXIT_FAILURE;
}
}
// shutdown receive operations since we're done
iResult = shutdown(ClientSocket, SD_RECEIVE);
if (iResult == SOCKET_ERROR) {
printf("shutdown failed with error: %d\n", WSAGetLastError());
closesocket(ClientSocket);
WSACleanup();
return EXIT_FAILURE;
}
// cleanup
closesocket(ClientSocket);
}
WSACleanup();
return 0;
}

Answer 1

This is a very confusing question as it asks one question in the title, but the content addresses a different problem (threads crashing).
To address the primary question: Microsoft did add a way to handle socket communications in a GUI thread friendly way: WSAAsyncSelect. This will send socket events as messages to your applications message queue - typically an invisible window is created to handle the messages.