recvfrom: Resource temporarily unavailable. Why?

Question

I'm running this piece of code several times (for a non-blocking recvfrom on a UDP socket):

struct timeval read_timeout;
read_timeout.tv_sec = 0;
read_timeout.tv_usec = 1000;
setsockopt(sockfd, SOL_SOCKET, SO_RCVTIMEO, &read_timeout, sizeof read_timeout);
ssize_t n = recvfrom(sockfd, recvline, sizeof(recvline), 0, NULL, NULL);
if (n < 0) {
    perror("recvfrom");
    return -1;
} else // ... normal usage

Sometimes the program stops and I get the following error from perror

recvfrom: Resource temporarily unavailable

What could the issue be?

@EugeneSh. thanks for your answer. I understand what the problem is, but how can I solve it? Can I ignore this problem and loop with recvfrom again? — Robb1, Jan 17 '18 at 16:43
Increase the timeout or make it completely blocking (if possible). — Eugene Sh., Jan 17 '18 at 16:48
@ikegami that means that actually I didn't understand the problem! I thought that using `setsockopt()` in such a way would simply let me skip the `recvfrom` if I wasn't receiving anything and go on with the following code... not making it return with an error! — Robb1, Jan 17 '18 at 17:08
Comments are not for new questions. Existing questions are not for new questions. If you have a question to ask, click [Ask Question](https://stackoverflow.com/questions/ask). — ikegami, Jan 17 '18 at 20:44

score 1 · Accepted Answer · answered Jan 17 '18 at 19:25

Just modify the code to do what you want. When you get an error, instead of calling perror unconditionally, check if it's a timeout. If it's not a timeout, then call perror and return. If it's a timeout, do whatever it is you want to do when you get a timeout.

recvfrom: Resource temporarily unavailable. Why?

1 Answers1