Linux: is here a read or recv from socket with timeout?

Question

Hello

How can I try to read data from socket with timeout? I know, select, pselect, poll, has a timeout field, but using of them disables "tcp fast-path" in tcp reno stack.

The only idea I have is to use recv(fd, ..., MSG_DONTWAIT) in a loop

Answer 1

Install a handler for SIGALRM, then use alarm() or ualarm() before a regular blocking recv(). If the alarm goes off, the recv() will return an error with errno set to EINTR.

Answer 2

You can use the setsockopt function to set a timeout on receive operations:

SO_RCVTIMEO

Sets the timeout value that specifies the maximum amount of time an input function waits until it completes. It accepts a timeval structure with the number of seconds and microseconds specifying the limit on how long to wait for an input operation to complete. If a receive operation has blocked for this much time without receiving additional data, it shall return with a partial count or errno set to [EAGAIN] or [EWOULDBLOCK] if no data is received. The default for this option is zero, which indicates that a receive operation shall not time out. This option takes a timeval structure. Note that not all implementations allow this option to be set.

struct timeval tv;

tv.tv_sec = 30;  /* 30 Secs Timeout */
tv.tv_usec = 0;  // Not init'ing this can cause strange errors

setsockopt(sockfd, SOL_SOCKET, SO_RCVTIMEO, (char *)&tv,sizeof(struct timeval));