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Concurrent Programming
Demystified: The SystemJ
Approach
Partha S Roop
Precision Timed Computing Group
Department of Electrical and Computer
Engineering
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Presentation Outline
Concurrency and reactivity
Motivation for SystemJ
SystemJ modeling from specification to
implementation – a designer’s perspective
Some implementation avenues.
IDE and Testing
Conclusions
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Concurrency
Embedded systems are highly concurrent. A game, for
example, has many concurrent processes to capture the IO
interaction and the modelling of actors.
Concurrency is not well supported in conventional languages:
Java concurrency is nondeterministic.
RTOSs offer direct support for concurrent processes and the
management of shared resources. However, they don’t
guarantee determinism and also have implementation
overheads.
Question: can we provide a thread-safe model of concurrency
while also providing efficient implementation avenues?
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What is SystemJ
A new programming language and associated tool-chain for
programming highly concurrent and distributed systems.
SystemJ is a language for programming Globally
Asynchronous but Locally Synchronous (GALS) systems.
Is based on Java that provides the OO encapsulation and
abstraction. This is combined with synchronous concurrency
of Esterel and asynchronous composition of CSP.
Ideal for programming distributed systems such as smart
camera, collaborative programming, medical electronics,
robot programming environments, simulators, and computer
games.
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Clock Domains and Reactions
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A simple synchronous program: The
ABRO
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ABRO in SystemJ
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The Asynchronous ABRO
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Sample Trace
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A Protocol Stack in SystemJ
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The Model in SystemJ
Three Reactions in
Synchronous Parallel
Two CDs in
Asynchronous Parallel
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One Reaction in Detail
Thread performing
lengthy address
computation
Thread performing
Coordination with the
CRC checker
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SystemJ Compilation Strategies


TReK (True Reactive
Kernel) – Java library;
dynamic resolution of
signal dependencies in
CDs
AGRC splits controldriven and data-driven
operations with clear
interface; static compiletime analysis of signal
dependencies;
sequentialized reactions
in CD
TReK
AGRC
Not full syntax
Full syntax
Missing
preemptions
All
preemptions
Library
Formal
Large memory
footprint
Smaller
memory
footprint
Relies on Java
threads
No reliance on
Java threads
Control and
data
interleaved
Separation of
data and
control
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Compiling SystemJ – AGRC Approach

SystemJ program
represented by
semantic preserving
Asynchronous Graph
Code (AGRC)

AGRC splits controldriven and data-driven
operations with clear
interface
Separates Java from
control part

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AGRC – Separation of Control and Data
 Compiler identifies
the blocks of code
that have to be
executed on JVM
 If the target is
JVM, then AGRC
representation
transformed into
Java code – runs
on JVM
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New Compilation and Execution
Strategies
SystemJ
SystemJ
AGRC
intermediate
format
AGRC
intermediate
format
Control code for
program flow
and reactivity
Java code for data
operations
Data calls
JVM
Returned results
Queued data calls
CVM
JVM
Returned results
Tandem Virtual Machine (TVM)

Control code for
program flow
and reactivity
Java code for data
operations
Control Virtual Machine
(CVM) is an interpreter of
a special instruction set
CP
Tandem processor

Control Processor (CP) is
a real processor
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Benchmarks
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Benchmarks
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Development Tools
 Eclipse based IDE
 Program editing functions
 GUI for debugger as a plug-in which extends debugger capability
and highlights reactions
 Compiler – with selectable execution target
 Debugger
 For JVM implementations
 For TVM and HMP implementations
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Development Environment
SystemJ
Source
line
EOT
Output
PC
Registers
Emitted
Signals
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Building Complex Software Systems
 SystemJ programs easily coexist each with the programs
written in other languages.
 Condition: other programs “understand” the signal
abstraction.
 Communication can be “direct” or through the operating
system (using sockets as universal mechanism for external
signals implementation).
 Execution platform is “hidden” by the operating system (can
be single and/or multicore and/or br distributed).
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Building Complex Software Systems
PHYSICAL ENVIRONMENT
Dedicated
Drivers
Signals
Complex
Software
System
Other
programs
SystemJ
Program 1
Operating
System
SystemJ
Program 2
Signals
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Software Test-Bench 1
 Environment emulator and observer of SystemJ design under test
(DUT) may be added as another clock domain.
 Minor modification necessary in the DUT.
SystemJ program/DUT
Existing clock domain
New reaction
to
communicate
with test-bench
Test-bench = SystemJ program =
DUT + EE (CD)
Testbench
channels
Environment
emulator and
observer
(clock domain)
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Software Test-Bench 2
 Environment emulator and observer of SystemJ design under test (DUT)
added as another SystemJ program
 No modification of DUT necessary
 DUT and Environment emulator (EE) can run on different processors/network
Test-bench = DUT +EE
They communicate through signals
SystemJ
program/DUT
Operating
System
Environment
emulator and
observer
(system)
EE
Test-bench signals
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Building Distributed Systems
 Distributed systems can be composed without changing individual SystemJ
programs
NETWORK
Computer 1
Computer N
Core 1
Core 2
SystemJ
Other
programs
Program
Operating
System
SystemJ
Program
Operating
System
PHYSICAL ENVIRONMENT
SystemJ
Program
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Qualitative comparison
Axum (Microsoft)
Concurrency Model
Asynchronous
Concurrency
Synchronous
Concurrency
Guaranteed
Determinancy
Actors
Yes
No
No
Go (Google)
Co(/Go)-routines
Yes
No
No
SystemJ (UoA)
GALS
Yes
Yes
Yes (Within a
single CD)
Communication
Mechanisms
Channels
Channels
Signals and
Channels
Pre-emption Support
No
No
Yes
Base Language(s)
.NET
Custom
Java
Size of Available
Libraries
Large (makes use of .NET
libraries)
Small
Huge (can use
any Java library)
Supported Platforms
Windows
Linux, Mac OSX, Android
Windows, Linux,
Mac OSX, Android
and Several
Custom HW
Platforms
Compiles to
CLR Bytecode
Native machine code
(x86/ARM)
Java Source →
Java Bytecode
Conclusions
 SystemJ addresses needs of future embedded and
distributed systems.
 System level approach to the design.
 GALS model of computation.
 Reuse of existing Java libraries.
 Range of target platforms.
 Flexibility – with or w/o OS.
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Conclusions
 Tandem processor and GALS hybrid multiprocessor are
platforms for constrained embedded applications.
 Compilation technology allows targeting any
combination of JVM Data processors and Reactive
Coprocessors.
 Performance improvement over pure JVM approaches.
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SystemJ Publications
 F. Gruian, P. Roop, Z. Salcic, I. Radojevic, SystemJ Approach to system-level Design,
Proceedings of Methods and Models for Co-Design Conference, Memocode 2006, Napa Valley
California, 2006, pp. 149-58. Piscataway, NJ, USA

A. Malik, Z. Salcic and P. S. Roop, Tandem Virtual Machine – An Efficient Execution Platform
for GALS Language SystemJ, Asia-South Pacific Conference on Computer Architecture, 2008,
p.1-8
 A. Malik, Z. Salcic, A. Girault, A. Walker, S.L. Lee: A customizable multiprocessor for Globally
Asynchronous Locally Synchronous execution, 7th International Workshop on Java
Technologies for Real-Time and Embedded Systems, ACM Proceedings, Madrid, 23-25
September, 2009, p.120-129
 A. Malik, Z. Salcic, P. Roop: SystemJ Compilation using the Tandem Virtual Machine
Approach, ACM Transactions on Design Automation of Electronic Systems, 14, (3), p-, 2009
 A. Malik, Z. Salcic, P. S. Roop and A. Girault. SystemJ: A GALS Language for System Level
Design, Journal of Computer Languages, Systems & Structures, COMLAN, Elsevier, to appear,
doi: 10.1016/j.cl.2010.01.001, 2010
 Z. Salcic and A. Malik: SystemJ Technology – Programming Without Borders, White Paper,
2010, www.systemjtechnology.com
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Acknowledgement of Contributions to
SystemJ Technology
 Zoran Salcic

 Avinash Malik

 Partha Roop

 Flavius Gruian


Luka Bartolec
Robert Connolly
Kyle Nicholas
Ivan Radojevic
Alain Girault




Wei-Tsun Sun
Elise Malard
Sung Chul Lee
Adam Walker
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Thank you!
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www.systemjtechnology.com
e-mail: [email protected]
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