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From: "Rolf" <rolf.ebert_nospam_@gmx.net>
Newsgroups: comp.lang.ada
Subject: tasksing and TCP sockets
Date: 30 Jan 2006 14:12:51 -0800
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Date: 2006-01-30T14:12:51-08:00
List-Id: <comp.lang.ada>

Consider an application that communicates with its environment via
sensors and actors. For testing purposes the low level access to the
sensor and actor data gets replaced by a TCP socket communication whose
other end simulates the world, i.e. the world simulation continuously
writes sensor data to the socket and accepts commands as actor data.

  +-----------------------+
  |                       |
  | application           |
  |                       |
  +-----------------------+
  |    h/w abstraction    |
  |  sensors  |  actors   |
  +-----------------------+
             |
         TCP client
             |
             |
             |
  TCP server that simulates the world


In a stripped down version I can succesfully connect to the server
(using GNAT.Sockets) and either read the sensor data *or* write actor
data. The program is currently split in two tasks. One tasks contains
the application code and the actor communication (using
type_id'output(channel)). The second tasks gets started during program
initialisation. It reads the data from the socket via
type_id'input(channel) and provides the data to the application through
a protected object.

The problem that I face is that the second task seems to starve the
first one. As soon as it is active, the application does not generate
debug output anymore.

Some background info: gcc-3.4.4 on Windows XP. Java for the world
simulation. The simulator sends about 20 packages =E0 11bytes every
100ms. The application sends typically 2-3 packages per second. I have
delay statements in both main loops (varied between 0.0 and 0.2
seconds).

My questions:
 - is that a reasonable tasking approach?
 - I don't know much about sockets (or better I don't remember much).
Does a waiting read (in the second task) block a write in the first
task?
 - how can I interrupt the waiting read task to force activity in the
main task?
 - what other hints can you give me?


TIA
   Rolf