sockets and timeouts

**newbie30** · 08-27-2009

We have this select statement

rc = select(fd+1, &fds, NULL, NULL, &tv);

now the timeout variable tv, say for example is set to 5.

Does this mean that this socket will timeout if no data is sent or received within the 5 secs?

Basically what i am trying to do is this:
I have a client/server, and the client will send info to server, and if server doesnt respond in 5 secs i want it to disconnect, this will be non blocking too

any ideas please?

**newbie30** · 08-27-2009

Sorry i probably wasnt clear in this question so will try again.

Using non blocking sockets.

If i have a client and server.
The client sends data to the server.

because the server is non blocking also, if i use the select command does that mean that no other client can talk to the server till its done with the select?

Whats my other options in getting the server to read data from more than one socket?

Thanks

**dwks** · 08-27-2009

Does this section from the manpage answer your first question?

Code:

       timeout is an upper bound on the amount of time elapsed before select()
       returns.  It may be zero, causing select() to return immediately. (This
       is useful for polling.) If timeout is NULL (no timeout),  select()  can
       block indefinitely.

**newbie30** · 08-27-2009

So if i have a clietn/server both non blocking and i want to send data across i should not use the select option on the server side???

I write some rough code here but hope you get what i mean as i dont have the code with me
Start with server

Code:

accept()
/*will do infinite loop
while(1)
{
      read(sockfd, buffer, sizeof(buffer));
      printf("Message is %s" buffer);
}

so if i start this server up and connect two clients will this loop catch all the data on the socket from the two clients?

Thanks

**dwks** · 08-27-2009

I don't know too much about this sort of thing, but read() only reads from one file descriptor. I'd imagine you'd have to do something like this:

Code:

repeat indefinitely:
    call accept() to receive incoming connections
    if any incoming connections were received, add the file descriptor to a set of descriptors
    call select(), giving it the set of file descriptors with a timeout of a few milliseconds or whatever
    call read() on the sockets which are ready for reading
    close any sockets which have been disconnected

The trouble is that you presumably want to receive incoming client connections even while other connections are not responding; so you need to call select() with a small (or zero) timeout. You'll have to have some other way of figuring out when each connection was last active.

As I said, though, I really don't know much about this. Read the man pages ("man 2 select", etc) and Beej's tutorial (google it, you'll find it).

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