NetNews Usenet Archive 1993 #1/NN_1993_1.iso/spool/comp/unix/programm/5853

Text File | 1993-01-07 | 2.6 KB | 61 lines

Newsgroups: comp.unix.programmer
Path: sparky!uunet!walter!porthos!delphinus!chw
From: [e-mail] (Charlie Woloszynski)
Subject: DGram sockets (UDP) and select on SunOS 4.1
Reply-To: [e-mail]
Organization: Bellcore
Date: Thu, 7 Jan 93 18:24:10 GMT
Message-ID: <[e-mail]>
Sender: [e-mail] (USENET System Software)
Lines: 49

From chw Thu Jan  7 13:15:44 1993
To: [e-mail]
Subject: Socket question


I am trying to use a socket (dgram, udp) between two processes and
I'm having some difficulty with select().  Select returns immediately,
telling me that the socket is ready for reading.  But, when I read
it, the recv() blocks until the second process actually sends some data.
Is this "normal" for datagram sockets and select?

Here is some more of the details:   I have two processes.  Each creates
a socket () (dgram, udp), bind()s it to a unique port, and connect()s to
the remote address (host, port).  Since these are dgram sockets, this
connect only set the remote address to use and receive from.  No real
connection is established.  Anyway, I assume that this lets the
kernel filter incoming datagrams to the appropriate socket this way.
No errors are indicated by the
return value, but the errno goes from 0 to EACCES (permission denied).
The man page indicates this error is only for UNIX domain addresses,
but I have used PF_INET exclusively for addressing.  The sockets I am
using are not in /etc/services or any other system file I can think
to look into.  Should they be (for dgram)?  If I
add them, is there any processes that need to be restarted to recognize this
change?

Now the first select call I do immediately returns (before the second
process send to it).  So, my code does a recv() which now blocks until
the second process sends something.  This characteristic repeats itself
endlessly (well, as long as my patience lasted, about three minutes
while I stewed and thought of other tests!!)

I also tried putting the socket into non-blocking mode, in which case
the recv() would return immediately (with errno=EWOULDBLOCK) and
then select would immediately indicate the socket was ready for input.

Any help would be greatly appreciated.

Charlie Woloszynski
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Charlie Woloszynski               MTS - ATM Technology and Applications
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