Visual C++ Sending message across thread - c++

Question

I am writting a small server application which has ServerSocket object waiting for and create connection socket.
Each connection has a SocketListener and a SocketSender for transfering data.
Each SocketListener is a separate thread. When a connection is disconnect by client, SocketListener send a message to ServerSocket notify that it is closing, so that ServerSocket can clear the handle for that connection from a list.
However, don't know why the message is not received by SocketListener thread. I have tried to narrow down the message filter, but no luck. Could someone help me with this.
DWORD ServerSocket::m_ThreadFunc() {
// Initialize Winsock
iResult = WSAStartup(MAKEWORD(2, 2), &wsaData);
if (iResult != 0) {
printf("WSAStartup failed\n");
return 1;
}
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
iResult = getaddrinfo(NULL, DEFAULT_PORT_STR, &hints, &result);
if (iResult != 0) {
printf("getaddrinfo failed\n");
WSACleanup();
return 1;
}
// Create a SOCKET for connecting to server
ListenSocket = socket(result->ai_family, result->ai_socktype, result->ai_protocol);
if (ListenSocket == INVALID_SOCKET) {
printf("socket failed\n");
freeaddrinfo(result);
WSACleanup();
return 1;
}
// Setup the TCP listening socket
iResult = bind(ListenSocket, result->ai_addr, (int)result->ai_addrlen);
if (iResult == SOCKET_ERROR) {
printf("bind failed\n");
freeaddrinfo(result);
closesocket(ListenSocket);
WSACleanup();
return 1;
}
freeaddrinfo(result);
iResult = listen(ListenSocket, SOMAXCONN);
if (iResult == SOCKET_ERROR) {
printf("listen failed\n");
closesocket(ListenSocket);
WSACleanup();
return 1;
}
// allow listener thread to report back its state
MSG msg;
ZeroMemory(&msg, sizeof(MSG));
//force create message queue
PeekMessage(&msg, NULL, WM_USER, WM_USER + 100, PM_NOREMOVE);
printf("Listing for clients on port %s \n", DEFAULT_PORT_STR);
while (listening) {
// Accept a client socket
ClientSocket = accept(ListenSocket, NULL, NULL);
if (ClientSocket != INVALID_SOCKET) {
printf("Client connected\n");
sender = new SocketSender(ClientSocket);
listener = new SocketListener(ClientSocket, this->m_threadId);
printf("Listener created\n");
listener->setSender(sender);
listener->startThread();
printf("Listener started\n");
listenerList.push_back(listener);
senderList.push_back(sender);
printf("Listener list size: %d \n", listenerList.size());
printf("Listener pushed to list\n");
//delete socket data if listener close itself due to connection lost or disconnect.
}
else {
int error = WSAGetLastError();
printf("accept failed\n");
switch (error) {
case 10093:
listening = false;
try {
closesocket(ListenSocket);
}
catch (...) {}
return 1;
}
}
printf("Check message queue for thread message\n");
//check thread message queue
//GetMessage(&msg, NULL, 0, 0); //this blocks untill a message is get.
PeekMessage(&msg, NULL, WM_USER, WM_USER + 100, PM_REMOVE);
if (msg.message == WM_USER + 1)
{
//ProcessCustomMessage(msg);
m_deleteListener((SocketListener*)msg.wParam);
printf("Recieved message from ThreadID: %d \n", msg.wParam);
}
printf("Recieved message from ThreadID: %d \n", msg.message);
printf("Server socket complete 1 loop\n");
}
return 0;
}
DWORD SocketListener::m_ThreadFunc() {
listening = true;
rapidxml::xml_document<> doc;
printf("Start thread with ID: %d \n", this->m_threadId);
printf("Parent Thread ID: %d \n", this->_iParentID);
while (listening) {
int iResult = recv(ClientSocket, recvbuf, recvbuflen, 0);
if (iResult > 0) {
printf("Bytes received: %d\n", iResult);
recvbuf[iResult - 1] = 0; // null terminate the string according to the length
// The message spec indicates the XML will end in a "new line"
// character which can be either a newline or caraiage feed
// Search for either and replace with a NULL to terminate
if (recvbuf[iResult - 2] == '\n' || recvbuf[iResult - 2] == '\r')
recvbuf[iResult - 2] = 0;
try {
doc.parse<0>(&recvbuf[0]);
HandleXMLMessage(&doc);
}
catch (...) {}
}
else {
printf("Thread %d is being closed, sending signal to parent (%d)\n", this->m_threadId, this->_iParentID);
if (PostThreadMessage(this->_iParentID, WM_APP + 1, NULL, NULL) == 0)
{
printf("Client cant send Message before closing the conn ! \n");
printf("Last error %d", GetLastError());
}
else {
printf("Client sent Closing Message successfully \n");
}
closesocket(ClientSocket);
return 1;
}
}
printf("Server terminate connection\n");
printf("Thread %d is closed, sending signal to parent (%d)\n", this->m_threadId,this->_iParentID);
PostThreadMessage(this->_iParentID, WM_USER + 1, (WPARAM)this->m_threadId, NULL);
return 0;
}
Thank you very much.

Answer 1

accept function is a blocking call, so it looks like after accepting first connection your loop gets stuck at
ClientSocket = accept(ListenSocket, NULL, NULL);
And does not check thread message queue until the next connection is made.
You also need to check the return result of PeekMessage to know whether message was actually peeked otherwise msg variable will contain garbage.