1
Poster Abstract: fVM, a hard real-time Java
implementation for cyber-physical systems
Filip Pizlo, Lukasz Ziarek, Jan Vitek
Abstract—Real-time Java is emerging as a platform for building mission-critical embedded systems. The real-time
variants of Java, including [3], [4], are attractive alternatives to Ada and C as they provide a cleaner, simpler, and safer
programming model. Unfortunately, current real-time Java implementations have trouble scaling down to very hard realtime embedded settings, where memory is scarce and processing power is limited. In this poster, we describe a new
real-time Java implementation, the fVM, intended for use in avionics, space, and cyber-physical systems.
F
1
I NTRODUCTION
S
CALING modern, mainstream languages
and their runtimes down to powerconstrained embedded settings is hard,
especially if real-time guarantees must be
ensured. While Java is emerging in a wide
variety of application domains, the availability
of standards-compliant Java implementations
for embedded systems is limited, especially if
automatic memory management is desired.
Over the past six years, our group at Purdue has been developing the Ovm [1], [6]
– a Java-in-Java metacircular virtual machine
that aims to provide hard real-time guarantees, while complying with a large subset of
the Java language. Development of Ovm has
resulted in the first UAV flight using avionics written in Java [1], [7] and the first opensource real-time garbage collector with high
throughput and good mutator utilization [5].
Though Ovm’s footprint is quite competitive
with other hard real-time VMs, it’s still larger
than we would desire. Its ability to perform
high-level compiler optimizations is also limited, leading to sub-optimal performance. Thus,
over the past year we have been developing a
new Java VM, the fVM, which applies lessons
learned from Ovm and applies them to create
• F. Pizlo, L. Ziarek, and J. Vitek are with the Department of
Computer Science, Purdue University, W. Lafayette, IN, 47909,
as well as Fiji Systems, LLC, Indianapolis, IN 46202.
E-mail: {filip,lziarek,jv}@cs.purdue.edu
a fast and light-weight virtual machine targetted at power-constrained embedded real-time
systems and cyber-physical systems.
2
F VM
D ESIGN
Like Ovm, fVM is designed as an ahead-oftime compiler for Java programs. Our goal is to
provide developers with an automated mechanism for converting high-level Java applications into small and compact real-time executables. fVM consists of two components: fVMc,
the compiler, which reads in Java bytecodes
and produces compact, high-performance machine code, and fVMr, a light-weight portable
runtime written in a combination of C and Java.
2.1
fVMr: the runtime component
fVM is designed to have a light-weight runtime inspired by the proven design philosophies of runtimes for languages such as C. The
runtime footprint is around 0.2 MB on IA-32.
fVMr provides the following functionality: (i) a
novel real-time garbage collector with provable
space bounds in the style of JamaicaVM [8],
but with multicore support, higher throughput
and tighter worst-case execution time (WCET)
bounds, (ii) a threading library that directly
maps Java threads to operating system threads,
and (iii) a complete implementation of the Java
Native Interface, a standard API for performing
calls between Java and C code. This simple
2
1.1
have 1000 classes or less can typically be compiled in under a minute resulting in a 1.5 MB
1.0
binary, of which 200 KB is the fVM runtime.
0.9
The rest is global data, debug information, and
executable code, including everything neces0.8
sary to support Java features such as JNI and
0.7
reflection.
The work that remains prior to a 1.0 release
0.6
is fixing bugs that are preventing the remainder
0.5
of the SPECjvm98 from executing, and complecompress
db
mpegaudio
GEOMEAN
tion of our real-time garbage collector. HowRelative execution time of fVM versus Ovm
ever, even with our current implementation,
Fig. 1. Performance of fVM versus Ovm on a small set fVM outperforms Ovm; see Fig. 1. Programs
of SPECjvm98 benchmarks. The Y-axis shows the relative compiled with fVM are on average 14% faster.
execution time of fVM versus Ovm. On average, programs
We believe that fVM is running slower than
run faster in fVM, taking roughly 14% less time to execute.
Ovm on the larger benchmark due to the incomplete garbage collector.
design has the benefit of allowing fVM to be
ported not just to large-scale main-stream op- 4 C ONCLUSION
erating systems like Windows, Linux, and Mac
We are developing a new Java virtual machine,
OS X, but also embedded hard real-time operfVM, targetted at power-constrained real-time
ating systems such RTEMS or vxWorks. Since
systems. By reducing the footprint and improvfVMr only relies on an OS threading library
ing performance, we hope to enable high-level
and some basic C functionality, applications
real-time Java applications to run seamlessly on
compiled with fVM can be run even on a very
hardware that previously could only support
minimal RTEMS profile, minimizing footprint
applications written in lower-level languages.
and maximizing performance.
2.2
fVMc: the compiler component
Our compiler converts Java bytecodes into a
low-level representation suitable for generating
either machine code or C code. Currently, we
generate compact and portable C code, allowing us to trivially port the compiler to a variety
of hardware and operating system platforms.
An optimizing machine code backend is in the
design stages. fVMc is designed to produce fast
code; thus, heavy emphasis is placed on eliminating dead or redundant code, and devirtualizing and inlining select method calls. These
optimizations allow the generation of code that
performas at levels close to those achieved by
production non-real-time Java virtual machines.
3
S TATUS OF F VM
The fVM is already capable of running
large Java applications, including half of the
SPECjvm98 benchmark suite. Programs which
R EFERENCES
[1] A. A RMBUSTER , J. B AKER , A. C UNEI , D. H OLMES ,
C. F LACK , F. P IZLO , E. P LA , M. P ROCHAZKA , AND
J. V ITEK, A Real-time Java virtual machine with applications
in avionics, ACM Transactions in Embedded Computing
Systems, 2007.
[2] J. A UERBACH , D. F. B ACON , B. B LAINEY, P. C HENG ,
M. D AWSON , M. F ULTON , D. G ROVE , D. H ART, AND
M. S TOODLEY, Design and implementation of a comprehensive
real-time Java virtual machine, in Conference on Embedded
software (EMSOFT), 2007.
[3] G. B OLLELLA , J. G OSLING , B. B ROSGOL , P. D IBBLE ,
S. F URR , AND M. T URNBULL, The Real-Time Specification for
Java, Addison-Wesley, 2000.
[4] JSR 302, Safety critical Java technology, 2007.
[5] F. P IZLO AND J. V ITEK, An empirical evalutation of memory
management alternatives for Real-time Java, in Real-Time Systems Symposium (RTSS), Dec. 2006.
[6] P URDUE, The Ovm virtual machine, www.ovmj.org.
[7] P URDUE,
Purdue
Researchers
Participate
in
Development
of
ScanEagle
UAV,
cs.purdue.edu/news/1-12-06scaneagle.htm
[8] F. S IEBERT, Real-time garbage collection in multi-threaded systems on a single processor, in Real-Time Systems Symposium
(RTSS), 1999.
[9] S UN M ICROSYSTEMS, Sun java real-time system,
java.sun.com/javase/technologies/realtime/,
2008.