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Groups > comp.lang.java.programmer > #15824
| From | Eric Sosman <esosman@ieee-dot-org.invalid> |
|---|---|
| Newsgroups | comp.lang.java.programmer |
| Subject | Re: Java processors |
| Date | 2012-07-05 14:31 -0400 |
| Organization | A noiseless patient Spider |
| Message-ID | <jt4mht$glm$1@dont-email.me> (permalink) |
| References | <5f101d00-4bc9-4750-939c-cd53605bfa0e@googlegroups.com> <jt4bqi$c2b$1@dont-email.me> <jt4kr2$mdd$1@news.albasani.net> |
On 7/5/2012 2:00 PM, BGB wrote:
> On 7/5/2012 10:28 AM, Eric Sosman wrote:
>> On 7/5/2012 11:01 AM, bob smith wrote:
>>> What ever happened to those processors that were supposed to run Java
>>> natively?
>>>
>>> Did Sun or anyone else ever make those?
>>
>> http://en.wikipedia.org/wiki/Java_processor
>>
>> (If you need help clicking links, just ask.)
>>
>
> and, of those, AFAIK, ARM's Jazelle was the only one to really gain much
> widespread adoption, and even then is largely being phased out in favor
> of ThumbEE, where the idea is that instead of using direct execution, a
> lightweight JIT or similar is used instead.
>
> part of the issue I think is that there isn't really all that much
> practical incentive to run Java bytecode directly on a CPU, since if
> similar (or better) results can be gained by using a JIT to another ISA,
> why not use that instead?
>
>
> this is a merit of having a bytecode which is sufficiently abstracted
> from the underlying hardware such that it can be efficiently targeted to
> a variety of physical processors.
>
> this is in contrast to a "real" CPU ISA, which may tend to expose enough
> internal workings to where efficient implementation on different CPU
> architectures are problematic (say: differences in endianess, support
> for unaligned reads, different ways of handling arithmetic status
> conditions, ...). in such a case, conversion from one ISA to another may
> come at a potentially significant performance hit.
>
> whereas if this issue does not really apply, or potentially even the
> output of the JIT will execute faster than it would via direct execution
> of the ISA by hardware (say, because the JIT can do a lot more advanced
> optimizations or map the code onto a different and more efficient
> execution model, such as transforming the stack-oriented code into
> register-based machine code), than there is much less merit to the use
> of direct execution.
In principle, a JIT could do better optimization than a
traditional compiler because it has more information available.
For example, a JIT can know what classes are actually loaded in
the JVM and take shortcuts like replacing getters and setters with
direct access to the underlying members. A JIT can gather profile
information from a few interpreted executions and use the data to
guide the eventual realization in machine code. Basically, a JIT
can know what the environment actually *is*, while a pre-execution
compiler must produce code for every possible environment.
On the other hand, a former colleague of mine once observed
that "Just-In-Time" is in fact a misnomer: it's a "Just-Too-Late"
compiler because it doesn't even start work until after you need
its output! Even if the JIT generates code better optimized for
the current circumstances than a pre-execution compiler could,
the JIT's code starts later. Does Achilles catch the tortoise?
--
Eric Sosman
esosman@ieee-dot-org.invalid
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Java processors bob smith <bob@coolfone.comze.com> - 2012-07-05 08:01 -0700
Re: Java processors Eric Sosman <esosman@ieee-dot-org.invalid> - 2012-07-05 11:28 -0400
Re: Java processors BGB <cr88192@hotmail.com> - 2012-07-05 13:00 -0500
Re: Java processors Eric Sosman <esosman@ieee-dot-org.invalid> - 2012-07-05 14:31 -0400
Re: Java processors BGB <cr88192@hotmail.com> - 2012-07-05 16:42 -0500
Re: Java processors Arne Vajhøj <arne@vajhoej.dk> - 2012-07-05 20:30 -0400
Re: Java processors BGB <cr88192@hotmail.com> - 2012-07-05 21:12 -0500
Re: Java processors Eric Sosman <esosman@ieee-dot-org.invalid> - 2012-07-06 00:13 -0400
Re: Java processors Roedy Green <see_website@mindprod.com.invalid> - 2012-07-06 13:26 -0700
Re: Java processors Gene Wirchenko <genew@ocis.net> - 2012-07-06 13:50 -0700
Re: Java processors Lew <lewbloch@gmail.com> - 2012-07-06 14:17 -0700
Re: Java processors Roedy Green <see_website@mindprod.com.invalid> - 2012-07-06 19:07 -0700
Re: Java processors BGB <cr88192@hotmail.com> - 2012-07-07 09:34 -0500
Re: Java processors Roedy Green <see_website@mindprod.com.invalid> - 2012-07-07 21:01 -0700
Re: Java processors BGB <cr88192@hotmail.com> - 2012-07-08 00:28 -0500
Re: Java processors Lew <noone@lewscanon.com> - 2012-07-07 23:00 -0700
Re: Java processors BGB <cr88192@hotmail.com> - 2012-07-08 10:20 -0500
Re: Java processors Lew <noone@lewscanon.com> - 2012-07-08 09:16 -0700
Re: Java processors Martin Gregorie <martin@address-in-sig.invalid> - 2012-07-08 17:46 +0000
Re: Java processors Lew <noone@lewscanon.com> - 2012-07-08 11:52 -0700
Re: Java processors Martin Gregorie <martin@address-in-sig.invalid> - 2012-07-08 21:41 +0000
Re: Java processors Lew <noone@lewscanon.com> - 2012-07-08 17:56 -0700
Re: Java processors Roedy Green <see_website@mindprod.com.invalid> - 2012-07-08 19:44 -0700
Re: Java processors Lew <noone@lewscanon.com> - 2012-07-09 23:41 -0700
Re: Java processors David Lamb <dalamb@cs.queensu.ca> - 2012-07-16 13:22 -0400
Re: Java processors Lew <lewbloch@gmail.com> - 2012-07-16 14:03 -0700
Re: Java processors Roedy Green <see_website@mindprod.com.invalid> - 2012-07-08 19:42 -0700
Re: Java processors Daniele Futtorovic <da.futt.news@laposte-dot-net.invalid> - 2012-07-10 01:13 +0200
Re: Java processors Lew <lewbloch@gmail.com> - 2012-07-09 16:26 -0700
Re: Java processors Roedy Green <see_website@mindprod.com.invalid> - 2012-07-11 15:41 -0700
Re: Java processors Daniele Futtorovic <da.futt.news@laposte-dot-net.invalid> - 2012-07-12 01:02 +0200
Re: Java processors Wanja Gayk <brixomatic@yahoo.com> - 2012-07-21 18:46 +0200
Re: Java processors Eric Sosman <esosman@ieee-dot-org.invalid> - 2012-07-21 13:05 -0400
Re: Java processors Wanja Gayk <brixomatic@yahoo.com> - 2012-07-21 19:23 +0200
Re: Java processors Eric Sosman <esosman@ieee-dot-org.invalid> - 2012-07-21 14:10 -0400
Re: Java processors Wanja Gayk <brixomatic@yahoo.com> - 2012-07-23 01:17 +0200
Re: Java processors Eric Sosman <esosman@ieee-dot-org.invalid> - 2012-07-22 20:15 -0400
Re: Java processors Daniele Futtorovic <da.futt.news@laposte-dot-net.invalid> - 2012-07-22 15:13 +0200
Re: Java processors Roedy Green <see_website@mindprod.com.invalid> - 2012-07-06 19:03 -0700
Re: Java processors Roedy Green <see_website@mindprod.com.invalid> - 2012-07-08 19:51 -0700
Re: Java processors Roedy Green <see_website@mindprod.com.invalid> - 2012-07-07 21:17 -0700
Re: Java processors Lew <noone@lewscanon.com> - 2012-07-07 23:04 -0700
Re: Java processors Roedy Green <see_website@mindprod.com.invalid> - 2012-07-08 09:29 -0700
Re: Java processors Lew <noone@lewscanon.com> - 2012-07-08 11:57 -0700
Re: Java processors Wanja Gayk <brixomatic@yahoo.com> - 2012-07-08 15:40 +0200
Re: Java processors BGB <cr88192@hotmail.com> - 2012-07-08 10:36 -0500
Re: Java processors Lew <lewbloch@gmail.com> - 2012-07-06 11:31 -0700
Re: Java processors Jim Janney <jjanney@shell.xmission.com> - 2012-07-05 13:02 -0600
Re: Java processors BGB <cr88192@hotmail.com> - 2012-07-05 16:09 -0500
Re: Java processors Jan Burse <janburse@fastmail.fm> - 2012-07-06 01:29 +0200
Re: Java processors Martin Gregorie <martin@address-in-sig.invalid> - 2012-07-06 00:42 +0000
Re: Java processors Roedy Green <see_website@mindprod.com.invalid> - 2012-07-06 13:53 -0700
Re: Java processors Martin Gregorie <martin@address-in-sig.invalid> - 2012-07-06 21:18 +0000
Re: Java processors Eric Sosman <esosman@ieee-dot-org.invalid> - 2012-07-06 18:17 -0400
Re: Java processors Martin Gregorie <martin@address-in-sig.invalid> - 2012-07-06 22:29 +0000
Re: Java processors Roedy Green <see_website@mindprod.com.invalid> - 2012-07-06 19:10 -0700
Re: Java processors BGB <cr88192@hotmail.com> - 2012-07-07 09:42 -0500
Re: Java processors Eric Sosman <esosman@ieee-dot-org.invalid> - 2012-07-07 10:58 -0400
(OT) Was: Re: Java processors Eric Sosman <esosman@ieee-dot-org.invalid> - 2012-07-07 11:38 -0400
Re: (OT) Was: Re: Java processors Gene Wirchenko <genew@ocis.net> - 2012-07-07 21:19 -0700
Re: (OT) Was: Re: Java processors "Peter J. Holzer" <hjp-usenet2@hjp.at> - 2012-07-08 12:15 +0200
Re: Java processors Gene Wirchenko <genew@ocis.net> - 2012-07-07 21:17 -0700
Re: Java processors Jim Janney <jjanney@shell.xmission.com> - 2012-07-05 19:14 -0600
Re: Java processors Roedy Green <see_website@mindprod.com.invalid> - 2012-07-06 13:34 -0700
Re: Java processors Jan Burse <janburse@fastmail.fm> - 2012-07-06 23:04 +0200
Re: Java processors Silvio Bierman <silvio@moc.com> - 2012-07-07 00:13 +0200
Re: Java processors Roedy Green <see_website@mindprod.com.invalid> - 2012-07-06 19:16 -0700
Re: Java processors "Peter J. Holzer" <hjp-usenet2@hjp.at> - 2012-07-08 11:37 +0200
Re: Java processors Roedy Green <see_website@mindprod.com.invalid> - 2012-07-06 13:24 -0700
Re: Java processors BGB <cr88192@hotmail.com> - 2012-07-07 10:06 -0500
Re: Java processors Roedy Green <see_website@mindprod.com.invalid> - 2012-07-06 05:22 -0700
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