如何在单个客户端上的UDP套接字上同时接收和发送数据

Question

I have to implement selectiveRepeat Mechanism on udp as it is in TCP. So in this respect i will be sending my window to the client and in same time will be expecting acks for sent data...I am trying to do this as shown below ... but in this code it sends data but does not recieve any ack.......can any one plz help

`fd_set rfds;
fd_set wfds;
FD_ZERO(&rfds);
FD_ZERO(&wfds);

struct timeval timeout;
timeout.tv_sec = 5;
timeout.tv_usec = 0; 

FD_SET(socket, &rfds);
FD_SET(socket, &wfds);

while( FBS < LBS )
{


    int result = select(socket+1, &rfds, &wfds, NULL, &timeout);


    if(FD_ISSET(socket, &rfds))
    {

         Recieve();
    }
    if(FD_ISSET(socket, &wfds))
    {

        Send( "Some data");


    }   

    FBS++;

}`

Answer 1

fd_set rfds;
fd_set wfds;
FD_ZERO(&rfds);
FD_ZERO(&wfds);
struct timeval timeout;
timeout.tv_sec = 5;
timeout.tv_usec = 0; 

FD_SET(socket, &rfds);
FD_SET(socket, &wfds);

while( FBS < LBS )
{


int result = select(socket+1, &rfds, &wfds, NULL, &timeout);


if(FD_ISSET(socket, &rfds))
{

     Recieve();
     FD_SET(socket, &wfds);     //set socket wirtable
}
if(FD_ISSET(socket, &wfds))
{

    Send( "Some data");
    FD_CLR(socket, &wfds); // reset socket writable

}   

FBS++;

UPDATE :

You need to remove socket from wfds after sending data FD_CLR(socket, &wfds). Because when you add socket in wfds and polling using select then select will always find that socket writable and will keep sending data infinitely untill socket it closed. You have to set it to writable only iff there is data available to send. In above scenario, at first set it as writable, then send data and remove it from wfds, then keep waiting for ACK