Please help me send message to multiple client using udp

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Hello guys
I want to send some text messages from server to many clients. client only show them on a messagebox. since there are many client, I get a udp socket, send data to it, and then closesocket. my problem is: after writing data to socket, If I immediately close the socket, message will be lost. where I should close the socket?
thanks in advance
mr.abzadeh
Edit: the original question was not clear, so I edited it
Edit: my code is added here(simplified)

SOCKET socket1 = socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP);
 ADDRINFOW * pAddr;
 ADDRINFOW hints;
 memset(&hints, 0, sizeof(hints));
 hints.ai_family = AF_INET;
 hints.ai_protocol = IPPROTO_UDP;
 hints.ai_socktype = SOCK_DGRAM;
 GetAddrInfoW( wszHostName, lpPortName, &hints, &pAddr);
 sendto( socket1, (const char *)pBuf, uSendLen, 0, pAddr->ai_addr, Addr->ai_addrlen);

 closesocket(socket1);//This kills socket and prevents message delivery

Posted 22-Feb-14 15:19pm

mr.abzadeh

Updated 23-Feb-14 20:14pm

v3

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Sergey Alexandrovich Kryukov 22-Feb-14 23:59pm

Why UDP? What is your purpose? Help with what? What's the problem?
—SA

mr.abzadeh 24-Feb-14 2:21am

I use TCP for communication between server and clients, starting at clients, responced by server. Sometimes conversations are started by server. Since I don't want to use two distinct ports, I decided to use UDP for messaging. the Admin at a client posts a message to server by TCP, which is mirrored to some or all of clients via UDP. it may or may not be tolerable if udp doesn't deliver message. Can you show me another plan to send messages to clients, originated at server? Since my question was very badly stated, I clarified and edited it.
My current question is this: In the following code, closesocket destroys socket very soon and prevents message delivery.

SOCKET socket1 = socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP);
ADDRINFOW * pAddr;
ADDRINFOW hints;
memset(&hints, 0, sizeof(hints));
hints.ai_family = AF_INET;
hints.ai_protocol = IPPROTO_UDP;
hints.ai_socktype = SOCK_DGRAM;
GetAddrInfoW( wszHostName, lpPortName, &hints, &pAddr);
sendto( socket1, (const char *)pBuf, uSendLen, 0, pAddr->ai_addr, Addr->ai_addrlen);

closesocket(socket1);//This kills socket and prevents message delivery

mr.abzadeh 23-Feb-14 14:07pm

I use TCP for communication between server and clients, starting at clients, responced by server. Sometimes conversations started by server. Since I don't want to use two distinct ports, I decided to use UDP for messaging. the Admin at a client posts a message to server by tcp, which is mirrored to some or all of clients via udp. it may or may not be tolerable if udp doesn't deliver message. Can you show me another plan to send messages to clients, originated at server? Since my question was very badly stated, I clarified and edited it.

[no name] 23-Feb-14 18:55pm

UDP is often used for what you suggest. Have you read up on UDP. Do you want some links on how to do this? What is your question?

mr.abzadeh 24-Feb-14 2:18am

I have read up on TCP and lesser on UDP. any link describing and help implementing UDP is appreciated. My current question is this: In the following code, closesocket destroys secket very soon and prevents message delivery.
SOCKET socket1 = socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP);
ADDRINFOW * pAddr;
ADDRINFOW hints;
memset(&hints, 0, sizeof(hints));
hints.ai_family = AF_INET;
hints.ai_protocol = IPPROTO_UDP;
hints.ai_socktype = SOCK_DGRAM;
GetAddrInfoW( wszHostName, lpPortName, &hints, &pAddr);
sendto( socket1, (const char *)pBuf, uSendLen, 0, pAddr->ai_addr, Addr->ai_addrlen);

closesocket(socket1);//This kills socket and prevents message delivery

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User 59241 · Accepted Answer · 2014-02-23T20:33:00

Solution 1

Why not just do it the way the documentation suggests? It may be productive to contemplate why sendto() returns a value.

http://msdn.microsoft.com/en-us/library/windows/desktop/ms740148(v=vs.85).aspx[^]

This may help you also:

http://gafferongames.com/networking-for-game-programmers/virtual-connection-over-udp/[^]

The examples here are good:
http://computing.unn.ac.uk/staff/cgmb3/teaching/sockets/DonahooWinAdaptsListings.pdf[^]

Posted 23-Feb-14 20:33pm

User 59241

Comments

mr.abzadeh 24-Feb-14 19:20pm

I have fuuly checked the return values in my code. Here I simplified the code for breafness.
I studied the links above, all are the principal materials about TCP and UDP

[no name] 24-Feb-14 19:33pm

Does the datagram arrive at the client if you don't close the socket? I assumed that was the first thing you tested.

mr.abzadeh 26-Feb-14 0:36am

Yes, It arrives. and even when I closesocket, 80% of times the message is delived. I don't know the resson of 20% fail is UDP fail or race condition where I close socket.

[no name] 26-Feb-14 0:44am

It is just an unreliable network. Try to read the spec for UDP - it explains all this. If you cannot live with this you need to implement a more reliable method involving handshaking such as TCP or the virtual UDP I gave you in the links.

mr.abzadeh 26-Feb-14 18:26pm

Thanks for your help. I assume it is the UDP not deliver message. I close this Post, But I have one more question: If the peer that will receive the message has been shut down without notifying, for example, due to power failure, will sendto block the thread? If so, How to overcome this?

[no name] 26-Feb-14 20:11pm

You still seem not to understand UDP.
"UDP is a simpler message-based connectionless protocol. In connectionless protocols, there is no effort made to set up a dedicated end-to-end connection. Communication is achieved by transmitting information in one direction, from source to destination without checking to see if the destination is still there, or if it is prepared to receive the information."
sendto() does not care whether recipients exist or not.

mr.abzadeh 27-Feb-14 16:03pm

Thanks, Thats right. now Every thing is OK. I changed my plan. I create a udp socket and reuse it, no call to closesocket is issued. This way messages arrive clients better than before. At my earlier plan, I created udp socket, called sendto, and then called sendsocket. The first message didnt arrive to clients. subsequent messages arrived 'naturally.

[no name] 27-Feb-14 18:58pm

I'm glad you got it working. I should have made the point that leaving the socket open as long as it may be needed is the normal way of doing this.