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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 SUNOS

socketpair

socketpair(3SOCKET)					     Sockets Library Functions					       socketpair(3SOCKET)

NAME

       socketpair - create a pair of connected sockets

SYNOPSIS

       cc [ flag ... ] file ... -lsocket -lnsl [ library ... ]
       #include <sys/types.h>
       #include <sys/socket.h>

       int socketpair(int domain, int type, int protocol, int sv[2]);

DESCRIPTION

       The  socketpair()  library call creates an unnamed pair of connected sockets in the specified address family domain, of the specified type,
       that uses the optionally specified protocol. The descriptors that are used in referencing the new sockets are returned in sv[0] and  sv[1].
       The two sockets are indistinguishable.

RETURN VALUES

       socketpair() returns -1 on failure and 0 on success.

ERRORS

       The call succeeds unless:

       EAFNOSUPPORT		       The specified address family is not supported on this machine.

       EMFILE			       Too many descriptors are in use by this process.

       ENOMEM			       There was insufficient user memory for the operation to complete.

       ENOSR			       There were insufficient STREAMS resources for the operation to complete.

       EOPNOTSUPP		       The specified protocol does not support creation of socket pairs.

       EPROTONOSUPPORT		       The specified protocol is not supported on this machine.

       EACCES			       The process does not have appropriate privileges.

ATTRIBUTES

       See attributes(5) for descriptions of the following attributes:

       +-----------------------------+-----------------------------+
       |      ATTRIBUTE TYPE	     |	    ATTRIBUTE VALUE	   |
       +-----------------------------+-----------------------------+
       |MT-Level		     |Safe			   |
       +-----------------------------+-----------------------------+

SEE ALSO

       pipe(2), read(2), write(2), socket.h(3HEAD), attributes(5)

NOTES

       This call is currently implemented only for the AF_UNIX address family.

SunOS 5.10							    10 Jan 2001 					       socketpair(3SOCKET)
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