I'm trying to create application where multiple instances will run on same machine and they will communicate together via UDP via the same port.
I was reading many threads on StackOverflow about it that it should be possible.
Though, when I open connection from each application instance I can see that each instance sends a message but only first instance (if first is closed then second...) receives that message.
I'm using ACE library for the communication. Excerpt from code:
ACE_SOCK_Dgram_Mcast dgram;
ACE_INET_Addr *listenAddress = new ACE_INET_Addr(12345, ACE_LOCALHOST);
dgram.open(*listenAddress);
ACE_INET_Addr peer_address;
char buffer[1024];
dgram.send(buffer, 256);
while (true)
{
if (dgram.recv(buffer, 256, peer_address, 0, &receiveLoopTimeout) != -1)
{
std::cout << "Received" << std::endl;
}
}
I also found out that if I call "dgram.join(*listenAddress)" then I get error, code ENODEV from the first instance of the app.
I'm not sure I understand what you are trying to do... send a message multicast so multiple receivers get it, or allow multiple processes to receive on the same UDP port unicast... I'm guessing the former.
You're using the ACE_SOCK_Dgram_Mcast class but with unicast addressing and operations. So only one instance will receive that message.
Check the ACE_wrappers/tests/Multicast_Test.cpp for examples of how to send and receive multicast.
Related
I was wondering, if it is possible to let one client communicate with multiple server at the same time. As far as I know, common browsers like for example firefox are doing exactly this.
The problem I have now is, that the client has to listen and wait for data from the server, rather then requesting it itself. It has to listen to multiple server at once. Is this even possible? What happens if the client is listening to server 1 and server 2 sends something? Is the package lost or will it be resend until the client communicates a successful receival? The protocol used is TCP.
edit: platform is Windows. Thanks for pointing this out Arunmu.
This is nothing different from regular socket programming using select/poll/epoll OR using thread-pool OR using process-per-connection OR whatever model that you know.
I can show you a rough pseudo-code on how to do it with epoll.
NOTE: None of my functions exist in C++, its just for explanation purpose. ANd I am ALSO assuming that you are on Linux, since you have mentioned nothing about the platform.
socket sd = connect("server.com", 8080);
sd.set_nonblocking(1);
epoll_event event;
event.data.fd = sd
epoll_ctl(ADD, event);
...
...
while (True) {
auto n = epoll_wait(events, 1);
for (int i : 1...n) {
if (events[i].data.fd == sd) // The socket added in epoll_ctl
{
std::thread(&Session::read_handler, rd_hndler_, sd); // Call the read in another thread or same thread
}
}
}
I hope you got the gist. In essence, think of server like a client and client like a server and you have your problem solved (kind of). Check out below link to know more about epoll
https://banu.com/blog/2/how-to-use-epoll-a-complete-example-in-c/
To see an fully functional server design using epoll, checkout:
https://github.com/arun11299/cpp-reactor-server/blob/master/epoll/reactor.cc
I have a server, which creates a separate thread for each new client
while ((client_socket = accept(server_socket, (sockaddr*)&client_info, &client_addr_size)))
{
nclients++;
HOSTENT *hst;
hst = gethostbyaddr((char*)&client_info.sin_addr.S_un.S_addr, 4, AF_INET);
printf("+%s [%s] new connect!\n", (hst) ? hst->h_name : "", inet_ntoa(client_info.sin_addr));
PRINTUSERS;
DWORD thID;
CreateThread(NULL, NULL, SexToClient, &client_socket, NULL, &thID);
}
Stream function every n seconds sends a message.(All streams do not do it at the same time).How to send a message to all clients at the same time?(broadcast)
I cant See Streamfunction. Without the corresponding function I cant give a perfect answer. Normally you would send (asynchron) in a for loop to all clients. The System would teen send the Massage to each Client one After Another. If you want to truly send a Massage to multiple clients at the Same time you need to use multicast.
(= sending one package which will arrive at multiple clients.) Unfortunately this is not possible using TCP, since TCP etablishes a (secure) point to point connection between one host and one client. You would have to use UDP. Remember that UDP wont care if the packages will arrive in the right Order, are correct or arrive at all.
I am learning Winsock and trying to create some easy programs to get to know it. I managed to create server which can handle multiple connections also manage them and client according to all tutorials, it is working how it was supposed to but :
I tried to make loop where I check if any of clients has disconnected and if it has, I wanted to close it.
I managed to write something which would check if socket is disconnected but it does not connect 2 or more sockets at one time
Anyone can give me reply how to make working loop checking through every client if it has disconnected and close socket ? It is all to make something like max clients connected to server at one time. Thanks in advance.
while (true)
{
ConnectingSocket = accept (ListeningSocket, (SOCKADDR*)&addr, &addrlen);
if (ConnectingSocket!=INVALID_SOCKET)
{
Connections[ConnectionsCounter] = ConnectingSocket;
char *Name = new char[64];
ZeroMemory (Name,64);
sprintf (Name, "%i",ConnectionsCounter);
send (Connections[ConnectionsCounter],Name,64,0);
cout<<"New connection !\n";
ConnectionsCounter++;
char data;
if (ConnectionsCounter>0)
{
for (int i=0;i<ConnectionsCounter;i++)
{
if (recv(Connections[i],&data,1, MSG_PEEK))
{
closesocket(Connections[i]);
cout<<"Connection closed.\n";
ConnectionsCounter=ConnectionsCounter-1;
}
}
}
}
Sleep(50);
}
it seems that you want to manage multiple connections using a single thread. right?
Briefly socket communication has two mode, block and non-block. The default one is block mode. let's focus your code:
for (int i=0;i<ConnectionsCounter;i++)
{
if (recv(Connections[i],&data,1, MSG_PEEK))
{
closesocket(Connections[i]);
cout<<"Connection closed.\n";
ConnectionsCounter=ConnectionsCounter-1;
}
}
In the above code, you called the recv function. and it will block until peer has sent msg to you, or peer closed the link. So, if you have two connection now namely Connections[0] and Connections[1]. If you were recv Connections[0], at the same time, the Connections[1] has disconnected, you were not know it. because you were blocking at recv(Connections[0]). when the Connections[0] sent msg to you or it closed the socket, then loop continue, finally you checked it disconnect, even through it disconnected 10 minutes ago.
To solve it, I think you need a book Network Programming for Microsoft Windows . There are some method, such as one thread one socket pattern, asynchronous communication mode, non-block mode, and so on.
Forgot to point out the bug, pay attention here:
closesocket(Connectons[i]);
cout<<"Connection closed.\n";
ConnectionsCounter=ConnectionsCounter-1;
Let me give an example to illustrate it. now we have two Connections with index 0 and 1, and then ConnectionsCount should be 2, right? When the Connections[0] is disconnected, the ConnectionsCounter is changed from 2 to 1. and loop exit, a new client connected, you save the new client socket as Connections[ConnectionsCounter(=1)] = ConnectingSocket; oops, gotting an bug. because the disconnected socket's index is 0, and index 1 was used by another link. you are reusing the index 1.
why not try to use vector to save the socket.
hope it helps~
I writing a small program that can Send File from Client -> Server (Send) and Server -> Client(Request).
Well done this part but the problems comes when:
1. I found the File on Server, How can I execute a cin on the client side?
2. How can I force my messages between Server and Client to be synced? I mean I dont want the Server to move to next step or freeze on the receive.
For Example(No Threading applied in this porblem):-
Server: Waiting a Message from Client.
Client: Send the Message.
Client: Waiting a Message from Client.
Server: Send the Message.
.....etc.
In a rare times the messages arrive on order but 99.999% of the time they don't and the program on two sides freeze.
The problem with the inorder messages was a thread on the client side who kept reading the inc replies without allowing the actual functions to see them.
However, about point 1.
I am trying in this code:
1. No shared resources so i am trying to define everything inside this function (part of it where the problem happening)
2. I was trying to pass this function to a thread so the server can accept more clients.
3. send & receive nothing special about them just a normal send/recv calls.
3. Question: if SendMyMessage & ReceiveMyMessage is going to be used by different threads, should I pass the socket to them with the message?
void ExecuteRequest(void * x)
{
RequestInfo * req = (RequestInfo *) x;
// 1st Message Direction get or put
fstream myFile;
myFile.open(req->_fName);
char tmp;
string _MSG= "";
string cFile = "*";
if(req->_fDir.compare("put") == 0)
{
if(myFile.is_open())
{
SendMyMessage("*F*");
cFile = ReceiveMyMessage();
// I want here to ask the client what to do after he found the that file exist on the server,
// I want the client to to get a message "*F*", then a cin command appear to him
// then the client enter a char
// then a message sent back to the server
// then the server continue executing the code
//More code
}
Client side:
{
cout <<"Waiting Message" <<endl;
temps = ReceiveMessage();
if(temps.compare("*F*") == 0)
{
cout <<"File found on Server want to:\n(1)Replace it.\n(2)Append to it." <<endl;
cin>>temps;
SendMyMessage(temps);
}}
I am using visual studio 2013
Windowx 7
thread am using: _beginthread (I removed all threads)
Regards,
On linux, there is a system call "select" using which the server can wait on the open sockets. As soon as there is an activity, like client wrote something, the server wakes up on that sockets and processes the data.
You are on windows platform. So :
http://msdn.microsoft.com/en-us/library/windows/desktop/ms740141%28v=vs.85%29.aspx
I am writing an XMLRPC client in c++ that is intended to talk to a python XMLRPC server.
Unfortunately, at this time, the python XMLRPC server is only capable of fielding one request on a connection, then it shuts down, I discovered this thanks to mhawke's response to my previous query about a related subject
Because of this, I have to create a new socket connection to my python server every time I want to make an XMLRPC request. This means the creation and deletion of a lot of sockets. Everything works fine, until I approach ~4000 requests. At this point I get socket error 10048, Socket in use.
I've tried sleeping the thread to let winsock fix its file descriptors, a trick that worked when a python client of mine had an identical issue, to no avail.
I've tried the following
int err = setsockopt(s_,SOL_SOCKET,SO_REUSEADDR,(char*)TRUE,sizeof(BOOL));
with no success.
I'm using winsock 2.0, so WSADATA::iMaxSockets shouldn't come into play, and either way, I checked and its set to 0 (I assume that means infinity)
4000 requests doesn't seem like an outlandish number of requests to make during the run of an application. Is there some way to use SO_KEEPALIVE on the client side while the server continually closes and reopens?
Am I totally missing something?
The problem is being caused by sockets hanging around in the TIME_WAIT state which is entered once you close the client's socket. By default the socket will remain in this state for 4 minutes before it is available for reuse. Your client (possibly helped by other processes) is consuming them all within a 4 minute period. See this answer for a good explanation and a possible non-code solution.
Windows dynamically allocates port numbers in the range 1024-5000 (3977 ports) when you do not explicitly bind the socket address. This Python code demonstrates the problem:
import socket
sockets = []
while True:
s = socket.socket()
s.connect(('some_host', 80))
sockets.append(s.getsockname())
s.close()
print len(sockets)
sockets.sort()
print "Lowest port: ", sockets[0][1], " Highest port: ", sockets[-1][1]
# on Windows you should see something like this...
3960
Lowest port: 1025 Highest port: 5000
If you try to run this immeditaely again, it should fail very quickly since all dynamic ports are in the TIME_WAIT state.
There are a few ways around this:
Manage your own port assignments and
use bind() to explicitly bind your
client socket to a specific port
that you increment each time your
create a socket. You'll still have
to handle the case where a port is
already in use, but you will not be
limited to dynamic ports. e.g.
port = 5000
while True:
s = socket.socket()
s.bind(('your_host', port))
s.connect(('some_host', 80))
s.close()
port += 1
Fiddle with the SO_LINGER socket
option. I have found that this
sometimes works in Windows (although
not exactly sure why):
s.setsockopt(socket.SOL_SOCKET,
socket.SO_LINGER, 1)
I don't know if this will help in
your particular application,
however, it is possible to send
multiple XMLRPC requests over the
same connection using the
multicall method. Basically
this allows you to accumulate
several requests and then send them
all at once. You will not get any
responses until you actually send
the accumulated requests, so you can
essentially think of this as batch
processing - does this fit in with
your application design?
Update:
I tossed this into the code and it seems to be working now.
if(::connect(s_, (sockaddr *) &addr, sizeof(sockaddr)))
{
int err = WSAGetLastError();
if(err == 10048) //if socket in user error, force kill and reopen socket
{
closesocket(s_);
WSACleanup();
WSADATA info;
WSAStartup(MAKEWORD(2,0), &info);
s_ = socket(AF_INET,SOCK_STREAM,0);
setsockopt(s_,SOL_SOCKET,SO_REUSEADDR,(char*)&x,sizeof(BOOL));
}
}
Basically, if you encounter the 10048 error (socket in use), you can simply close the socket, call cleanup, and restart WSA, the reset the socket and its sockopt
(the last sockopt may not be necessary)
i must have been missing the WSACleanup/WSAStartup calls before, because closesocket() and socket() were definitely being called
this error only occurs once every 4000ish calls.
I am curious as to why this may be, even though this seems to fix it.
If anyone has any input on the subject i would be very curious to hear it
Do you close the sockets after using it?