Subject:
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Re: RCX and Java
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Newsgroups:
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lugnet.robotics
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Date:
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Tue, 4 May 1999 20:35:29 GMT
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Original-From:
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Gary Hughes <GHUGHES@TARDIS.avoidspamCOM>
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Viewed:
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919 times
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Ola Liljedahl <olli@enea.se> wrote:
> Aren't robots real time systems?
> Isn't the RCX meant to be a component in such real time systems?
>
> Java (as implemented by current virtual machines) is NOT suitable
> as a platform for building real time systems. The implementation of
> garbage collection is not deterministic and may take a very long
> time to execute. You Emacs users out there should recognise the problem...
MIT had their annual Lego robot race a month or so back, and they were
ALL running Java. Not on RCXs though; they were using some kind of
StrongARM running Linux as the programmable brick.
You can make Java GC more deterministic by disabling automatic GC. It is
a command line option to the JDK JVM (-noasyncgc). Then you at least get to
control when or if GC takes place. And of course you can write your own
GC methods if you wish.
> We should make the distinction between real time systems and embedded
> systems. Java is fine for embedded systems with no real time requirements.
There are people building real time systems with deterministic response
requirements in Java. There are people building new JVMs specifically for
deterministic real time applications, with very different GC
characteristics.
There is an effort underway, sponsored by NIST (US Gov't National Inst. of
Standards and Testing), to define a set of standard requirements for RT
Java.
> In my line of business I see some Java being used in real time systems.
> But never for real time purposes, only for low priority (as regards to
> real time properties) operation and maintenance.
I see a surprising amount of interest in Java from the real time community,
although they seem to be leaning heavily away from the Sun JVM. I don't
know if that is driven by technical or licensing/cost concerns (or both).
gary
--
Did you check the web site first?: http://www.crynwr.com/lego-robotics
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Message has 1 Reply:
 | | Re: RCX and Java
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| (...) Both, at least last year. Sun has recently gone to open source for the JVM but previously their license fees were very expensive. Technically, there are better choices wrt real-time/embedded issues. Fred ---...--- Fred Rose Ph: 612.951.7106 (...) (25 years ago, 4-May-99, to lugnet.robotics)
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