Socket A(local_address);
void enviar(sockaddr_in remote_address, std::atomic<bool>& quit){
std::string message_text;
Message message;
while(!quit){
std::getline(std::cin, message_text);
if (message_text != "/quit"){
memset(message.text, 0, 1024);
message_text.copy(message.text, sizeof(message.text) - 1, 0);
A.send_to(message, remote_address);
}
else {
quit = true;
}
}
}
void recibir(sockaddr_in local_address, std::atomic<bool>& quit){
Message messager;
while(!quit){
A.receive_from(messager, local_address);
}
}
int main(void){
std::atomic<bool> quit(false);
sockaddr_in remote_address = make_ip_address("127.0.0.1",6000);
std::thread hilorec(&recibir,local_address, std::ref(quit));
std::thread hiloenv(&enviar,remote_address, std::ref(quit));
hiloenv.join();
hilorec.join();
}
Hi! I'm trying to make a simple chat with sockets. I want the program to finish when I write "/quit". I'm trying this with an atomic bool variable called quit. The problem is when I write "/quit" quit will be 'true' and the hiloenv thread will be finish, but hilorec, which is to receive the messages, will be blocked until i receive a message because of the recvfrom() function. How i can solve this?
Sorry for my english and thanks!
Shutdown the socket for input. That will cause recvfrom() to return zero as though the peer had closed the connection, which will cause that thread to exit.
I would send some special (e.g. empty) message to A socket from main thread when quit is detected. In this case your while(!quit) ... loop will finish and so the thread.
If you want to create a single thread app, then use epoll or select apis. If you want to stick to your current design, then you can create your socket having timeout set. Please look for How to set socket timeout in C when making multiple connections? for details. SO when you do quit, the waiting thread will come out of recv or send after the timout and then thread will join and your application can quit gracefully.
Thanks for the answers. I managed to fix it, If anyone is interested how:
std::thread hilorec(&recibir,local_address);
std::thread hiloenv(&enviar,remote_address);
while(!quit){}
pthread_cancel(hilorec.native_handle());
pthread_cancel(hiloenv.native_handle());
hilorec.join();
hiloenv.join();
Related
I'm currently working on simple HTTP server. I use Winsock and standard threads from C++11. For each connected (accepted) client there is new thread created.
std::map<SOCKET, std::thread> threads;
bool server_running = true;
while(server_running) {
SOCKET client_socket;
client_socket = accept(listen_socket, NULL, NULL);
if(client_socket == INVALID_SOCKET) {
// some error handling
}
threads[client_socket] = std::thread(clientHandler, client_socket);
}
clientHandler function looks generally like this:
while(1) {
while(!all_data_received) {
bytes_received = recv(client_socket, recvbuf, recvbuflen, 0);
if(bytes_received > 0) {
// do something
} else {
goto client_cleanup;
}
}
// do something
}
client_cleanup: // we also get here when Connection: close was received
closesocket(client_socket);
And here we come to my problem - how to handle all the threads which ended but haven't been joined with main thread and references to them still exist in threads map?
The simplest solution would be probably to iterate over threads frequently (e.q. from another thread?) and join and delete those which returned.
Please share your expertise. :)
PS. Yes, I know about thread pool pattern. I'm not using it in my app (for better or worse). I'm looking for answer concerning my current architecture.
Simple solution? Just detach() after you start the thread. This will mean that once the thread terminates the resources will be cleaned up and you don't need to keep the std::map<SOCKET, std::thread> threads.
std::thread(clientHandler, client_socket).detach();
Otherwise create a thread-safe LIFO queue where during cleanup you push the socket to it.
Then in the main loop you alternately check accept and that queue and when the queue has sockets in them you do threads.erase(socket); for each socket in the queue.
However if you do that then you may as well putt he LIFO in the other direction and use a thread pool.
I need a code construction for my project which waits for some time, but when there is an interrupt (e.g. incoming udp packets) it leaves this loop, does something, and after this restart the waiting.
How can I implement this? My first idea is using while(wait(2000)), but wait is a void construct...
Thank you!
I would put the loop inside a function
void awesomeFunction() {
bool loop = true;
while (loop) {
wait(2000);
...
...
if (conditionMet)
loop = false;
}
}
Then i would put this function inside another loop
while (programRunning) {
awesomeFunction();
/* Loop ended, do stuff... */
}
There are a few things I am not clear about from the question. Is this a multi-threaded application, where one thread handles (say) the UDP packets, and the other waits for the event, or is this single-threaded? You also didn't mention what operating system this is, which is relevant. So I am going to assume Linux, or something that supports the poll API, or something similar (like select).
Let's assume a single threaded application that waits for UDP packets. The main idea is that once you have the socket's file descriptor, you have an infinite loop on a call to poll. For instance:
#include <poll.h>
// ...
void handle_packets() {
// m_fd was created with `socket` and `bind` or `connect`.
struct pollfd pfd = {.fd = m_fd, .events = POLLIN};
int timeout;
timeout = -1; // Wait indefinitely
// timeout = 2000; // Wait for 2 seconds
while (true) {
pfd.revents = 0;
poll(&pfd, 1, timeout);
if ((pfd.revents & POLLIN) != 0) {
handle_single_packet(); // Method to actually read and handle the packet
}
if ((pfd.revents & (POLLERR | POLLHUP)) != 0) {
break; // return on error or hangup
}
}
}
A simple example of select can be found here.
If you are looking at a multi-threaded application, trying to communicate between the two threads, then there are several options. Two of which are:
Use the same mechanism above. The file descriptor is the result of a call to pipe. The thread sleeping gets the read end of the pipe. The thread waking get the write end, and writes a character when it's time to wake up.
Use C++'s std::condition_variable. It is documented here, with a complete example. This solution depends on your context, e.g., whether you have a variable that you can wait on, or what has to be done.
Other interrupts can also be caught in this way. Signals, for instance, have a signalfd. Timer events have timerfd. This depends a lot on what you need, and in what environment you are running. For instance, timerfd is Linux-specific.
Consider the example code below (I typed it up quickly as an example, if there are errors it doesn't matter - I'm interested in the theory).
bool shutDown = false; //global
int main()
{
CreateThread(NULL, 0, &MessengerLoop, NULL, 0, NULL);
//do other programmy stuff...
}
DWORD WINAPI MessengerLoop( LPVOID lpParam )
{
zmq::context_t context(1);
zmq::socket_t socket (context, ZMQ_SUB);
socket.connect("tcp://localhost:5556");
socket.setsockopt(ZMQ_SUBSCRIBE, "10001 ", 6);
while(!shutDown)
{
zmq_msg_t getMessage;
zmq_msg_init(&getMessage);
zmq_msg_recv (&getMessage, socket, 0); //This line will wait forever for a message
processMessage(getMessage);
}
}
A thread is created to wait for incoming messages and to handle them appropriately. The thread is looping until shutDown is set to true.
In ZeroMQ the Guide specifically states what must be cleaned up, namely the messages, socket and context.
My issue is: Since recv will wait forever for a message, blocking the thread, how can I shut down this thread safely if a message is never received?
The blocking call will exit in a few ways. First, and this depends on your language and binding, an interrupt (Ctrl-C, SIGINT, SIGTERM) will exit the call. You'll get back (again, depending on your binding) an error or a null message (libzmq returns an EINTR error).
Second, if you terminate the context in another thread, the blocking call will also exit (libzmq returns an ETERM error).
Thirdly, you can set timeouts on the socket so it will return in any case after some timeout, if there's no data. We don't often do this but it can be useful in some cases.
Finally, what we do in practice is never do blocking receives but use zmq_poll to find out when sockets have messages waiting, then receive from those sockets. This is how you scale out to handling more sockets.
You can use non-blocking call flag ZMQ_DONTWAIT
while(!shutDown)
{
zmq_msg_t getMessage;
zmq_msg_init(&getMessage);
while(-1 == zmq_msg_recv(&getMessage, socket, ZMQ_DONTWAIT))
{
if (EAGAIN != errno || shutDown)
{
break;
}
Sleep(100);
}
processMessage(getMessage);
}
Whenever zmq context is destroyed, zmq_msg_recv will receive a -1. I use this as the terminating condition in all of my code.
while (!shutdown)
{
..
..
int rc = zmq_msg_recv (&getMessage, socket, 0);
if (rc != -1)
{
processMessage;
}
else
break;
}
Remember to destroy the zmq context at the end of your main() for a proper clean-up.
zmq_ctx_destroy(zctx);
Lets say you have a class say SUB (subscriber) that manages the receive of your ZMQ messages. In the destructor or exit function of your main function/class, call the following:
pub->close();
///
/// Close the publish context
///
void PUB::close()
{
zmq_close (socket);
zmq_ctx_destroy (context);
}
This will enable that 'recv' blocking terminates with error message that you can ignore. The application will exit comfortably in the right way. This is the right method. Good luck!
im currently attempting to create server and client application that use winsock, with a main program I need to have a second thread to always be listening for data.
This communication is non blocking. I am really having trouble in finding a way of communicating between threads, an example of what im looking for is: Server sends a string to the client e.g. "viewData" and this kind of information will be fetched by the main thread and then a specific function may also be called.
Here is an example of my thread, i am creating this using _beginthread( (void(*)(void*))SocketReceive, 0, (void*)&ohuman );
//thread focused on listening to connection
void SocketReceive( comms* ohuman)
{
char buffer[1000];
int inDataLength;
std::string contents;
for(;;)
{
if(!ohuman->getGameOn())
{
// Display message from server
memset(buffer,0,999);
inDataLength=recv((INT_PTR)ohuman->getSocket(),buffer,1000,0);
contents = std::string(buffer); //create a string from the char array for easy access
//only display if we get some content
if(inDataLength > 0)
{
//???DealWithMessage(
int nError=WSAGetLastError();
if(nError!=WSAEWOULDBLOCK&&nError!=0)
{
std::cout<<"Winsock error code: "<<nError<<"\r\n";
std::cout<<"Server disconnected!\r\n";
// Shutdown our socket
shutdown((INT_PTR)ohuman->getSocket(),0x01);
// Close our socket entirely
closesocket((INT_PTR)ohuman->getSocket());
break;
}
}
}
_endthread();
}
I also saw this site which is supposed to help out with ITC, any advice on this->
http://derkarl.org/itc/
With a straightforward main loop, I am interested in any approach that might work, I've been trying to figure this out for a couple of days with no luck, any help is greatly appreciated.
You can either have a shared variable(with locks around it) and both threads poll/write to it, or you can register callback functions between the threads and call the other thread on some event.
I have an interesting (to me) problem... There are two threads, one for capturing data from std input and sending it through socket to server, and another one which receives data from blocking socket. So, when there's no reply from server, recv() call waits indefenitely, right? But instead of blocking only its calling thread, it blocks the overall process! Why this thing occurs?
boost::mutex nvtMutex;
boost::mutex strMutex;
boost::mutex quitMutex;
bool quit = false;
void *processServerOutput(void *arg)
{
NVT *nvt = (NVT*)arg;
while(1)
{
// Lock the quitMutex before trying to access to quit variable
quitMutex.lock();
if(quit)
{
quitMutex.unlock();
pthread_exit(NULL);
}
else
quitMutex.unlock();
// Receive output from server
nvtMutex.lock();
nvt->receive();
cout << Util::Instance()->iconv("koi8-r", "utf-8", nvt->getOutBuffer());
nvtMutex.unlock();
// Delay
sleep(1);
}
}
void *processUserInput(void *arg)
{
NVT *nvt = (NVT*)arg;
while(1)
{
// Get user's input
//cin.getline(str, 1023);
sleep(3);
strcpy(str, "hello");
// If we type 'quit', exit from thread
if(strcmp(str, "quit") == 0)
{
// Lock quit variable before trying to modify it
quitMutex.lock();
quit = true;
quitMutex.unlock();
// Exit from thread
pthread_exit(NULL);
}
// Send the input to server
nvtMutex.lock();
nvt->writeUserCommand(Util::Instance()->iconv("utf-8", "koi8-r", str));
nvt->send();
nvtMutex.unlock();
}
}
You are holding the nvtMutex inside the call to NVT::recv. Since both threads need to lock the mutex to make it through an iteration, until NVT::recv returns the other thread can't progress.
Without knowing the details of this NVT class, it's impossible to know if you can safely unlock the mutex before calling NVT::recv or if this class does not provide the proper thread safety you need.
If your code is implemented correctly, recv blocks only the thread that invokes it.
If this isn't the case for you, show the minimal code sample that demonstrates the problem.