CS452 - Real-Time Programming - Fall 2009

Lecture 19 - Task Structure


Anthropomorphic Programming

We all, most programmers included, have effective intuitions about human relations

Tasks are independent entities

Servers and Attendant Tasks

Why do servers need attendant tasks?

1. Proprietor with a Notifier

Proprietor `owns' a service, which usually means a resource.

Kernel is handling hardware in this example

Notifier Code for a UART

Proprietor/Notifier Code for a UART


  1. Notifier is usually of higher priority than server
  2. When, and how, do interrupts get turned on and/or cleared?
  3. Who coordinates hardware ownership?
  4. We have made the code

2. Using a Courier

Simplest is best

Notifier Code

Courier Code

Proprietor Code


This gets you through a bottleneck where no more than two events come too fast.

Remember that all the calls provide error returns. You can/should use them for error recovery

Another possible arrangement for initialization

Distributed gating

3. Using a Warehouse

Add a warehouse between the courier and the notifier.

Notifier Code

Warehouse Code

Courier Code

Proprietor Code


This structure clears up problems when the notifier runs too fast for the server.

Two issues:

  1. Handles bottlenecks of all sizes.

    Define `bottleneck'.

  2. Server could be buffered on the other side

    Called a guard.

What this amounts to is

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