select() on sockets with timeout

Question

Inside the read FD_SET I have several sockets:

the main socket listening for new connections
accepted sockets listening for incoming data.

I set the timeout for 30 seconds and called select(). I quickly noticed the behavior is different for each:

When a new client connects on the listening port, it returns immediately from blocking.
When an already connected client sends a message, it blocks for the entire 30 seconds.

Is there a way I can make it return immediately in the second case?

Generally, I'd anticipate a code bug. Can you paste in your FD_SET and your select calls please? — Will
– Will, Commented Nov 9, 2009 at 8:44
I think your response to 1) might be causing 2). What is your response to 1)? Posting your code would help. — Martin Del Vecchio
– Martin Del Vecchio, Commented Nov 9, 2009 at 13:34

Bob · Accepted Answer · 2009-11-09 10:07:03Z

2

My guess is either you aren't including all your sockets in the correct fd_set or you aren't passing in the highest numbered file descriptor plus 1 as the first parameter (nfds below) to the select call.

select(nfds, &readfds, &writefds, &execptfds, &timeout);

answered Nov 9, 2009 at 10:07

Bob

312 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

Nikolai Fetissov · Accepted Answer · 2009-11-09 15:49:47Z

1

One of the most common errors with select(2) is not re-initializing fd_sets before calling select() again.

answered Nov 9, 2009 at 15:49

Nikolai Fetissov

84.6k13 gold badges118 silver badges175 bronze badges

Comments

Roman Nikitchenko · Accepted Answer · 2009-11-09 08:47:28Z

0

I constantly use such select()s without any problem.

Probably you do something wrong with accepted sockets waiting on data. Could you please post code fragment? Especially most important is how you set first select() parameter.

answered Nov 9, 2009 at 8:47

Roman Nikitchenko

13k8 gold badges80 silver badges115 bronze badges

Collectives™ on Stack Overflow

select() on sockets with timeout

3 Answers 3

Comments

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

Comments

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related