Setting timeout time for TCP sockets.

pops13 · 06-08-2011, 03:49 AM

Hi,

I have written simple TCP server-client programs in 'C' on my RHEL 5 64 bit.
I want to add SEND and RECEIVE timeout for this socket; so that if server is not responding in given time, request will get timeout instead of waiting in "recv" call.
But I failed to do so. can anybody help around it OR can redirect me to some link that will explain this.

Thanks in advanced.

NM04 · 06-08-2011, 05:41 AM

hi pops,

The easiest is to setup an alarm and have connect be interrupted with a signal (see UNP 14.2):

signal( SIGALRM, connect_alarm ); /* connect_alarm is you signal handler */
alarm( secs ); /* secs is your timeout in seconds */
if ( connect( fs, addr, addrlen ) < 0 )
{
if ( errno == EINTR ) /* timeout */
...
}
alarm( 0 ); /* cancel alarm */

regards,
nm04

pops13 · 06-08-2011, 11:01 AM

Thanks NM for responding with solution...

But this you tell about connect;
1) Is this applicable to "recv" and "send" system calls as well.
2) Is there any other way, other than signal handling; like we dose in case of normal sockets as follows,

Quote:

if ((sd = socket(AF_INET, SOCK_STREAM, 0)) == -1) {
perror("socket");
exit(1);
}

if (setsockopt (sd, SOL_SOCKET, SO_RCVTIMEO, (char *)&timeout,
sizeof(timeout)) < 0)
error("setsockopt failed\n");

NM04 · 06-09-2011, 05:19 AM

pops,

it should be applicable to send & recv functions i have not checked, but one thing if you apply timeout it will not connect then how will it proceed towards send & recv functions ?

pops13 · 06-10-2011, 01:34 AM

NM,

I need to set timeout to "send" and "recv" only, not to "connect".

So after connection, if server is not responding within timeout period, client must not wait longer than timeout period.
Dose this makes sense?

Thanks,
Pops.

NM04 · 06-10-2011, 07:07 AM

yes that does make sense, I told you that alarm should work on send and recv functions.

Code:

There are three ways to place a timeout on an I/O operation involving a socket.

1. Call alarm, which generates the SIGALRM signal when the specified time has 
expired. This involves signal handling, which can differ from one implementation
to the next, and it may interfere with other existing calls to alarm in the process.

2. Block waiting for I/O in select, which has a time limit built in, instead of blocking
in a call to read or write.

3. Use the newer SO_RCVTIMEO and SO_SNDTIME) socket options. The problem
with this approach is that not all implementations support these two socket options.

Each is appropriate, depending on the specific circumstances. I hope this helps.

kind regards,

pops13 · 06-10-2011, 09:31 AM

Thanks NM...
that will really help.

Let me work a little on option 2 you provided as well.

Quote:

2. Block waiting for I/O in select, which has a time limit built in, instead of blocking
in a call to read or write.