JAVA-BASED REAL-TIME PROGRAMMING

1. Introduction
pany depends on the reliability of the computer system, etc.) special measures
must be taken to limit the possible (faulty) influences of one software function
on another part of the system. Therefore, we have to abandon programming
in C or C++ for large/complex systems. Instead, we have to base the core
development on a more scalable language (and run-time system) that prevents
direct access to memory, for instance via pointers. Java (and partly C#) is
such a language. Still, programming in C is appropriate for device drivers,
which do need to directly access the hardware. For similar reasons of scalability,
Microsoft had to go from their Win32+MFC C/C++-oriented standard to
the Microsoft®.NET Framework with C# in order to stay competitive in the
long run. Here, we will go some steps further, considering also small embedded
systems and severe timing demands.
Java does not solve all problems, and it is not the best possible solution, but
it has the qualities that we need to build higher-level functionality and tools.
Furthermore, it is based on open standards and has the desired support and
(free) availability. However, there is a common misconception in both industry
and academia: The Java language is not suitable for real-time programming.
In the sequel it will be explained why this is not true, and how it can and
should be done.
Given the nice properties of the Java programming language, such as security
and platform independence, we want to exploit the advantages for development
of real-time control software, even for systems subject to severe demands
on performance and predictability. Even though Java from the beginning was
intended for programming embedded control devices, some industrially important
control aspects were never dealt with, and the major development and
success has been within Internet programming of interactive applications such
as applets.
We will approach the real-time issues via established web-programming
and concurrency techniques, which will reveal a few deficiencies of the standard
Java platform. A real-time package (class library) and a few run-time
extensions will be presented. The usage of these additions to create high
performance real-time control software is then described in a real-time programming
chapter which is central the topic of this book. The reader should
then gain additional understanding and programming skill by studying the
remaining chapters about scheduling, processes, and applications.
To illustrate the notions of concurrency, real-time, and control (in the
order mentioned) two simple application examples now follows.
Example 1: The LEGO ® -brick machine
Computer control of a machine for manufacturing LEGO-bricks, as depicted
in Figure 1.1, implies two requirements on the software:
1. The temperature of the plastic material should be measured and con-
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