Groups > comp.lang.java.programmer > #15911

Re: Java processors

From	Lew <noone@lewscanon.com>
Newsgroups	comp.lang.java.programmer
Subject	Re: Java processors
Date	2012-07-09 23:41 -0700
Organization	albasani.net
Message-ID	<jtgiqn$17i$1@news.albasani.net> (permalink)
References	(8 earlier) <jtch2b$m9u$1@localhost.localdomain> <jtcktv$i25$1@news.albasani.net> <jtcuqk$q15$1@localhost.localdomain> <jtda71$66j$1@news.albasani.net> <lbhkv7l18m68jannfp4m07intmv49fqito@4ax.com>

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Roedy Green wrote:
> Lew wrote, quoted or indirectly quoted someone who said :
>
>> It wouldn't make sense to keep old compilations around.
>
> The whole reason to abandon them is because they are ram pigs. Holding
> onto them would defeat that purpose.

No, that's only three quarters of the reason.

The other quarter is the uselessness of optimized code that isn't needed 
because the scenario for which it's optimized has vanished.

The point of caching the compilation would be to take advantage of its 
recurrence. But the code was invalidated for its runtime assumptions no longer 
pertaining.

It takes a while for a hot spot to settle into a position of prominence. So 
the optimization had to have been pretty useful for a while to even exist. For 
it to become invalid, some hefty changes had to have occurred, such as an 
addition of another reference to a previously enregistered value or a new 
thread-contention profile.

For that previously-invalidated compilation to have value again, the runtime 
circumstances would have to shift again in its favor, and persist for a while 
to make it a hot spot.

Cross the probability of that happening with the long time before the "cached" 
compilation can return to play, with ample resources available to profile and 
analyze the hot spot that's required even if you think you have a "cache", and 
you see why it isn't just memory parsimony at play. It's the whole, "Why 
manage a cache that doesn't with complexity that buys you nothing?" philosophy.

Code complexity, lack of benefit, maintenance costs and likelihood of bugs or 
even degraded performance might even outweigh memory parsimony as 
considerations. I'm guessing the HotSpot engineers simply didn't want to 
implement a dumb-ass mechanism.
-- 
Lew
Honi soit qui mal y pense.
http://upload.wikimedia.org/wikipedia/commons/c/cf/Friz.jpg

Thread

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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