rharrison33 rharrison33 - 1 year ago 182
C Question

Errno: 11, Resource Temporarily Unavailable

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");
}

alk alk
Answer Source

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() times 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 nonblocking 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 ... ;-)

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