Download Enhancements to Java for Real Time Systems

Enhancements to
Java for Real Time
Systems
Theresa Dsena
CSE 666 - Fall 2006
Prof. Ganesan
Contents
Limitations of Standard Java
 Overview of RTSJ
 Guiding Principles of RTSJ
 Enhancements to Standard Java
 Concluding notes on RTSJ
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Limitations of Standard Java

Major Weakness
 Garbage

The garbage collector de-allocates objects from the memory
heap in no particular order. This non-deterministic behavior
could interrupt application execution for unpredictable
intervals of time
 Thread
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Collection
Scheduling
The JVM (Java Virtual Machine) relies on the host operating
systems thread scheduler. The operating system must be
capable of real-time scheduling
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Overview of RTSJ
The Real Time for Java Experts Group
(RTJEG) has been developing Real Time
Specification for Java (RTSJ) since 1999
under the Java community process
 RTSJ specifies enhancements to standard
Java, specifically for JVM and creation of
real time API
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Guiding Principles of RTSJ
Applicability to all Java environments
 Backward compatibility
 Write once, run anywhere
 Current real time practices and future
implementations
 Priority to predictable execution
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Enhancements to Standard Java
Thread scheduling and dispatching
 Memory management
 Thread synchronization
 Asynchronous event handling
 Asynchronous transfer of control
 Asynchronous thread termination
 Physical memory access
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Enhancements to Standard Java Thread Scheduling

RTSJ requires a base scheduler that
provides
 Preemptive
and priority based execution
 A minimum of 28 unique priorities

Define classes for execution eligibility and
schedule feasibility
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Enhancements to Standard Java Memory Management
Garbage collection in standard Java is
unsuitable for real-time threads
 RTSJ introduces the concept of memory
areas

memory – Standard Java heap
 Immortal memory – Shared among threads
 Scoped memory – For objects with a welldefined lifetime
 Heap
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Enhancements to Standard Java –
Thread synchronization
Priority queuing on synchronized blocks
 Implementation of Java keyword
Synchronized includes algorithm for
priority inversion
 Wait free queues
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Enhancements to Standard Java –
Asynchronous event handling
Real time application must respond to
asynchronous real world events
 RTSJ includes

 Asynchronous
events
 Asynchronous event handlers
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Enhancements to Standard Java –
Asynchronous thread termination
Drastic and asynchronous changes in the
real world may require a java thread to
safely transfer its control and terminate
 RTSJ includes thread interruption with
Asynchronous Transfer of Control (ATC)
thread handlers
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Enhancements to Standard Java –
Physical memory address

RTSJ includes direct access to physical
memory

A class that allows programmers byte level
access to physical memory
 A class that allows creation of objects in
physical memory
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Concluding notes
Java’s main problem for use in real time
applications is unsuitable memory
management
 RTSJ originated from the desire to use
Java in real time applications
 Real time Java is emerging
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References
http://www.rtsj.org
 http://www.itl.nist.gov/div897/ctg/real-time
 http://www.developer.com/java
 http://www.cs.cmu.edu/~nbeckman
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Thank You