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Full Discussion: Sockets and File descriptors
Top Forums Programming Sockets and File descriptors Post 92437 by gstlouis on Sunday 11th of December 2005 11:56:24 AM
Old 12-11-2005
Sockets and File descriptors
I am in a Systems programming class this semester, and our current project is to write a program utilizing sockets and fork. For the project, I decided to make my own instant messaging program. I have the code completed, but I have a problem that keeps old clients from communicating with new clients. The way it is currently set up has 2 programs, a client and a server. The server is always running. Each time a client connects, it forks off a child process to handle communication with that client, then the parent goes back to listening for new clients. On the client side, a connection to the server is made and communication is done with its associated server child process. Each time the server forks, it passes the updated table of file descriptors to its new child. However, child processes that already exist don't have record of the new file descriptor, which keeps them from being able to communicate to other users.

Take this example. Client A signs on. Then Client B. Client B can send messages to Client A, but Client A cannot send messages to client B because Client B signed on after client A, so he doesn't have the file descriptor for B. Client C then signs on. He can communicate with A and B because he has a current list of file descriptors for the users. But B cannot communicate with C and A can't communicate with either. I obviously would like all clients to communicate with one another no matter when they signed on.

Essentially, I would like a way to update file descriptors on all of the children each time a new client signs on. But that may not be the best solution to the problem. All I really need is a way for clients to communicate no matter when they signed on and without creating a seperate socket between each client. Any ideas?

Thanks for your help.
 

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LEARN ABOUT DEBIAN

xpa

xpa(7)								SAORD Documentation							    xpa(7)

NAME

       XPA -  Public Access to Data and Algorithms

SYNOPSIS

       This document is the Table of Contents for XPA.

DESCRIPTION

       The XPA messaging system provides seamless communication between many kinds of Unix programs, including X programs and Tcl/Tk programs.	It
       also provides an easy way for users to communicate with XPA-enabled programs by executing XPA client commands in the shell or by utilizing
       such commands in scripts.  Because XPA works both at the programming level and the shell level, it is a powerful tool for unifying any
       analysis environment: users and programmers have great flexibility in choosing the best level or levels at which to access XPA services,
       and client access can be extended or modified easily at any time.

       A program becomes an XPA-enabled server by defining named points of public access through which data and commands can be exchanged with
       other client programs (and users).  Using standard TCP sockets as a transport mechanism, XPA supports both single-point and broadcast mes-
       saging to and from these servers.  It supports direct communication between clients and servers, or indirect communication via an interme-
       diate message bus emulation program. Host-based access control is implemented, as is as the ability to communicate with XPA servers across
       a network.

       XPA implements a layered interface that is designed to be useful both to software developers and to users.  The interface consists of a
       library of XPA client and server routines for use in C/C++ programs and a suite of high-level user programs built on top of these
       libraries.  Using the XPA library, access points can be added to Tcl/Tk programs, Xt programs, or to Unix programs that use the XPA event
       loop or any event loop based on select().  Client access subroutines can be added to any Tcl/Tk, Xt, or Unix program. Client access also is
       supported at the command line via a suite of high-level programs.

       Choose from the following topics:

       o   Introduction to XPA [xpaintro(7)]

       o   Access Point Names and Templates [xpatemplate(7)]

       o   Getting Common Information About Access Points [xpacommon(7)]

       o   Communication Methods [xpamethod(7)]

       o   Communication Between Hosts [xpainet(7)]

       o   Distinguishing Users [xpausers(7)]

       o   XPA User Programs

	   o   xpaget: get data and info [xpaget(1)]

	   o   xpaset: send data and info [xpaset(1)]

	   o   xpainfo: send info alert [xpainfo(1)]

	   o   xpaaccess: get access point info [xpaaccess(1)]

	   o   xpamb: message bus emulation [xpamb(1)]

	   o   xpans: the XPA name server [xpans(1)]

       o   XPA Server Routines

	   o   XPANew: define a new access point [xpanew(3)]

	   o   XPACmdNew: define a new command access point [xpacmdnew(3)]

	   o   XPACmdAdd: add a command [xpacmdadd(3)]

	   o   XPACmdDel: delete a command [xpacmddel(3)]

	   o   XPAInfoNew: define an info access point [xpainfonew(3)]

	   o   XPAFree: free an access point [xpafree(3)]

	   o   XPAMainLoop: event loop for select server [xpamainloop(3)]

	   o   XPAPoll: poll for XPA events [xpapoll(3)]

	   o   XPACleanup: release reserved XPA memory [xpacleanup(3)]

	   o   XPA Server Macros: accessing structure internals [xpamacros(3)]

	   o   XPA Race Conditions: how to avoid them [xparace(3)]

	   o   XPA Out of Memory (OOM) errors [xpaoom(3)]

       o   XPA Client Routines

	   o   XPAOpen: open a persistent client connection [xpaopen(3)]

	   o   XPAClose: close persistent client connection [xpaclose(3)]

	   o   XPAGet: get data [xpaget(3)]

	   o   XPASet: send data or commands [xpaset(3)]

	   o   XPAInfo: send an info alert [xpainfo(3)]

	   o   XPAGetFd: get data and write to an fd [xpagetfd(3)]

	   o   XPASetFd: read data from and fd and send [xpasetfd(3)]

	   o   XPANSLookup: look up an access point [xpanslookup(3)]

	   o   XPAAccess: get access info [xpaaccess(3)]

	   o   The XPA/Xt Interface: Xt interface to XPA [xpaxt(7)]

	   o   The XPA/Tcl Interface: Tcl interface to XPA [xpa(3tcl)]

       o   Tailoring the XPA Environment

	   o   Environment Variables [xpaenv(7)]

	   o   Access Control [xpaacl(7)]

       o   Miscellaneous

	   o   Where to Find Example/Test Code

	   o   User Changes Between XPA 1.0 and 2.0

	   o   API Changes Between XPA 1.0 and 2.0

	   o   What Does XPA Stand For, Anyway?

version 2.1.14							   June 7, 2012 							    xpa(7)
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