Errno: 11, Resource Temporarily Unavailable
c, sockets, udp
Solution
When calling `recvfrom()` on a blocking socket and a time out had been set using `setsockopt()` it is normal to get the error `EAGAIN (11)` in case the call to `recvfrom()` timed out (that is: no data was received in the time period specified as time out).
Verbatim from `man recvfrom`:
RETURN VALUE
...
ERRORS
... .
EAGAIN or EWOULDBLOCK The socket is marked non-blocking and the receive operation would block, or a receive timeout had been set and the timeout expired before data was received. ...
To get around this: Just call `recvfrom ()` again ... ;-)
Problem
I am using c sockets to implement a reliable UDP protocol. I am using the following code to set a timeout on a socket in which I'm waiting for an acknowledgement. I am not sure why I am getting errno 11, resource temporarily unavailable. ``` //set timer for recv_socket struct timeval tv; tv.tv_usec = TIMEOUT_MS; if(setsockopt(rcv_sock, SOL_SOCKET, SO_RCVTIMEO,&tv,sizeof(tv)) < 0){ printf("Error setting the socket timeout.\n"); } int recv_msg_len; if(recv_msg_len = recvfrom(rcv_sock, ackBuffer,sizeof(ackBuffer), 0, (struct sockaddr *) &servAddr2, &fromSize) < 0){ //timeout reached printf("Error Reporting: %d : %s\n", errno, strerror(errno)); num_timeouts++; } ``` I have also tried the select method that was mentioned in the comments. I have the following code inside a loop, but the recvfrom never times out. ``` fd_set set; FD_ZERO(&set); /* empties the set */ FD_CLR(rcv_sock,&set); /* removes FD from the set */ FD_SET(rcv_sock,&set); /* adds FD to the set */ if(select(rcv_sock + 1, &set, NULL, NULL, &tv) < 0){ printf("\nError Reporting: %d : %s\n\n", errno, strerror(errno)); return -1; } if(!FD_ISSET(rcv_sock,&set)){ /* true if FD is in the set */ printf("socket is not set properly.\n"); } ```