CS476/576

Assignment #5

Due Midnight, Tuesday   Nov 20, 2001

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NAME

tcpline - A  program to reate a chain of processes connected with tcp sockets.

tcpline [<Rhost>  <Nproc>]

    The program creates Nproc processes (the default value of Nproc is 2) and each process is connected to its next process with a tcp socket as shown in the next  Figure. The odd numbered processes (number 1, 3, 5, ..etc)  runs on the localhost (i.e., where the tcpline command started) while the even numbered processes (number 2, 4, 6, ...etc) runs on the Remote host Rhost (the default value of Rhost is the localhost.)

Upon the creation of the the last  process,  the last process  will send a message to the first process via  the "tcpline" (the "tcpline" is the (n-1) tcp connections between the n processes) indicating to the user to start providing  input (this is similar to what took place in the pipeline  of assignment #4) .

Any line typed by the user travels across the "upstream" of the  tcpline (an upstream is from the first to the last  process) and then travels back through the "downstream" of the tcpline (the downstream is from the last to the first process) and then displayed back to  the user via the stdout of the first process. Therefore every line typed be the user is  displayed back after a round trip delay  over the tcpline. Each process introduces a 1 second delay in the upstream of  the tcpline which means that a message will return back to the user after at least N seconds dealy  (the  additional delay is due  of the overhead of sending the message using the tcp protocol).

When the user types CTRL-D, the processes are terminated in the order of their creation, i.e., the 1^th process dies first and the N^th process dies last (note this is different from the  assignment #4, where processes are terminated in the reverse order of their creation).

Unlike assignment #4, the even numbered processes may run on a remote host  and therefore may have no access to the stdout  and the stderr (i.e., file descriptors 1 and 2) that are usually associated with TTY and therefore we  need to:

1. create a UPD Server on the the localhost and  each process sends to it  the messages that need to be displayed on the TTY. Every message received by the the UDP Server from any process is displayed at the TTY preceded  with the <host-name:port-number> of the message sender.
2. create a file under /home/<username>/tcplineDIR/process<i> and each process  writes  its stderr messages in its file. The UDP Server file is named process0.


To get a feeling and gain more details about the specification
of this program, execute my own solution under: /home/cs476/tcpline

See the output file of running this  program twice, one with no argumnets
and another with two arguments: Examples.

NOTES:

• First,  telnet tolab(remember do NOT telnet to fast!)
• Copy the tcpline binary code  from ~cs476 to you home directory.

You MUST have a copy of the program in your homedirectory  since the program use rsh to run the program on a another host.
• The first time the program is executed with no arguments:

> tcpline
This creates two process at the localhost ("pitfall")
• The second time the program is executed with two arguments:

> tcpline dot 4
This creates four process, the odd numbered at "pitfall" and the even numbered at "dot", another machine the "lab" alias.
• The contents of the files under tcplineDIR are shown after each execution.


Hints:

• use remote shell (rsh) in the background to run tcpline at Rhost:
rsh  <Rhost>  "tcpline <args>" &
• use dup2 to replace stderr with a  a file descriptor fd:
dup2(fd, 2)