Delivery-Date: Sun Oct  5 16:18:02 2008
Message-Id: <200810052323.m95NNeuN007684@bourbon.usc.edu>
To: cs551@merlot.usc.edu
Subject: Re: Regarding connection establishment
Date: Sun, 05 Oct 2008 16:23:40 -0700
From: Bill Cheng <william@bourbon.usc.edu>

Someone wrote:

  > We are trying to implement the initial TCP connection between 2 beacon nodes.
  > When 2 threads are invoked, both of them run through the client and
  > server side of the code.
  > Initially, a thread comes up and tries to "connect" (like a client),
  > and the connection is refused 'coz no one is there to "listen".
  > Then this same thread tries to do a "bind" and then a "listen". Should
  > these be done on the same sockfd as the "connect" ? When we tried
  > using the same socket, we got a Bind Error.

Your server thread (the one that calls bind() and accept())
needs to be a separate thread from your client threads (the
one that calls connect()).  These client threads here are the
ones where you *initiate* connections to its neighbors.
Let's call this Type One client thread.

There is a 2nd type of client threads.  These are the ones
where another node initiates connection to this ndoe.  After
accept() returns, your server thread would create a child
thread to handle the connection.  Let's call this Type Two
client thread.

  > And would the second thread also be using the same socket as its mentioned that:
  > "For the purpose of this project, you must  use the same socket for
  > the connection from A to B and from B to A"
  > 
  > Could you please clarify this ?

If node A is connected to ndoe B, from node A's point of
view, it should be using either a Type One client thread
or a Type Two client thread, *but not both*.  For either
type, node A will be using the same socket for both reading
and writing.

You need to think back...  When you wrote your client code
for warmup project #1, your client first write to the socket
and then it reads from the same socket.  Similarly, your
server forks off a child to handle the connection.  The
child process first read the socket and the write to the
same socket.  So, on either side, there is only one socket.
(The master socket held by the server is *not* the one
that's used for reading and writing.)
--
Bill Cheng // bill.cheng@usc.edu <URL:http://merlot.usc.edu/william/usc/>