Problem Using SIGIO for interrupt driven socket I/O.

[Hemant Rotithor]

I would like to mention that I am not familiar with the internals
 of UNIX and my interest and problem is as a user at the system 
call level.

I am doing experiment in distributed computing on a network of VAX
stations running Ultix 3.0.

The application program is initially started on one machine. 
This machine then starts the same application program on four
other machines.
Each machine opens one listen port (stream socket) to which the
other machines can send messages. I have enabled asynchronous
notification of data received on the listen port using fcntl
calls and set up a handler for SIGIO signal.

The other four machines initially send one message each to the
initiating machine. The initiator correctly receives these four
messages by 4 interrupts (SIGIO) on its listen port. The problem is
after the 4 interrupts there is an additional interrupt generated,
there is no data to read on the port and the machine blocks in accept call.

I would like to know where the additional SIGIO is coming from when
4 messages are sent and received.
Is this a OS feature or possible problem with my program and what is 
the best way to deal with this.

I will appreciate any response. Thanking you in advance.

-- 
Hemant G. Rotithor (606)258-2656       * E-mail: hemant at ms.uky.edu or
Elect. Engg., 206 Old Mining Building  *         rotithor at engr.uky.edu     
University of Kentucky, KY 40506-0046